Analysis method for control interaction influence of converter model

Abstract

The invention discloses a method for analyzing control interaction influence of a converter model. The method comprises the following steps: S1, constructing a converter model comprising a control-admittance model of a network-following converter and a control-impedance model of a network-constructing converter; s2, constructing an interconnection system model related to the converter model, and solving a modal characteristic value of the system; s3, positioning a key dominant control loop according to the modal characteristic value of the system; and S4, extracting a key dominant control loop, analyzing an interaction mechanism between the dominant control loop and other parts of the system, and completing interaction influence analysis. The method can accurately and comprehensively reflect the control interaction effect of the interconnection system.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to a method for analyzing control interaction effects of a converter model. Background Art

[0002] The penetration of a high proportion of power electronic devices has greatly changed the stability and dynamic characteristics of modern power systems. The simultaneous grid connection of new energy devices controlled by Grid-Following (GFL) and Grid-Forming (GFM) is becoming the norm. However, the dynamic characteristics of these two control methods are significantly different, and the stability mechanism of the system in the interconnected scenario has not been effectively revealed. How to analyze the interaction between the internal controls of different types of converters has been a widely concerned issue in the academic community in recent years.

[0003] At present, the analysis of controller interaction in interconnected systems containing grid-following and grid-forming converters has the following challenges:

[0004] 1. There is still a lack of effective mechanism analysis methods for the small disturbance stability problem of interconnected systems. The control interaction analysis methods for single-machine grid-connected systems, such as the synchronous dominant loop method, cannot be extended to multi-machine interconnected systems with different control methods.

[0005] 2. The converter in the multi-machine interconnected system contains control loops with multiple time scales. The analysis of the oscillation mechanism of the interconnected system needs to take into account the combined influence of multiple controls, which requires that the analysis method must have the ability to consider multiple controls at the same time.

[0006] Although the existing methods can reflect the control interaction of interconnected systems including grid-following and grid-forming converters to a certain extent, there are still certain shortcomings. Since the interconnected system contains multiple synchronous converters, the operating conditions of the system are more complex and changeable. It is difficult to accurately and comprehensively reflect the control interaction of the interconnected system using traditional impedance analysis or eigenvalue analysis, which limits the applicable scenarios of the analysis. Summary of the invention

[0007] In order to solve the above-mentioned shortcomings of the existing stability analysis methods for interconnected systems of grid-following and grid-forming converters, the present invention provides an analysis method for the control interaction effects of a converter model.

[0008] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a method for analyzing the control interaction influence of a converter model, comprising:

[0009] S1. Constructing a converter model including a control-admittance model of a grid-following converter and a control-impedance model of a grid-building converter;

[0010] S2. Construct an interconnected system model about the converter model and solve the modal eigenvalues ​​of the system;

[0011] S3. Locate the key dominant control loop based on the modal eigenvalues ​​of the system;

[0012] S4. Extract the key dominant control loop, analyze the interaction mechanism between the dominant control loop and the rest of the system, and complete the interaction impact analysis.

[0013] Further: In S1, the converter model is equivalent to a controlled voltage source with mixed voltage and current control, and the overall dq domain admittance of the converter model is for:

[0014]

[0015] Where I is the 2×2 identity matrix, G I (s) and G II (s) are all controlled coefficients, Z f and Y Cf Respectively represent the filter inductance L f and capacitor C f The dq domain impedance and admittance are expressed as follows:

[0016]

[0017]

[0018] Where s is the Laplace operator, ω0 is the fundamental angular frequency of the system, R f is the filter resistor, L f For the filter inductor.

[0019] Further: for the control-admittance model of the grid-following converter, the outer loop adopts fixed active power control and the inner loop adopts dq decoupled current control;

[0020] Determine the sequence impedance Z corresponding to the control-admittance model of the grid-type converter GFL The methods include:

[0021] S101. According to the characteristics of the control-admittance model of the grid-following converter, the corresponding controlled coefficient is calculated, and its expression is:

[0022]

[0023]

[0024] Among them, V cd0 and I cd0 are the voltage and current values ​​of the converter in steady state, represents the transfer function of the inner loop current PI control; represents the transfer function of the outer loop active power PI control; and are the proportional parameter and integral parameter of current control respectively, and They are the proportional parameter and integral parameter of active power control respectively;

[0025] S102, according to the controlled coefficient of the control-admittance model of the grid-following converter, calculate the corresponding sequence impedance Z GFL , whose expression is:

[0026]

[0027] Among them, G P , G PLL and G C They are the closed-loop transfer functions of active power control, PLL control and current control respectively.

[0028] Further: for the control-impedance model of the grid-type converter, the outer loop adopts constant dq voltage decoupling control, the inner loop adopts constant dq current decoupling control, and the synchronous control loop adopts virtual synchronous generator control;

[0029] Determine the sequence impedance Z corresponding to the control-impedance model of the grid-connected converter GFM The methods include:

[0030] S111. According to the characteristics of the control-impedance model of the grid-connected converter, the corresponding controlled coefficient is calculated, and its expression is:

[0031]

[0032]

[0033] in, The transfer function of the outer loop voltage PI control is, represents the transfer function of the virtual synchronous generator control; J is the virtual inertia parameter, D p is the virtual damping parameter;

[0034] S112. Calculate the corresponding sequence impedance Z according to the controlled coefficient of the control-impedance model of the grid-type converter GFL , whose expression is:

[0035]

[0036]

[0037]

[0038] Among them, Δθ GFM is the phase angle difference between the local reference coordinate system of the control-impedance model of the grid-type converter and the global reference coordinate system of the system, ω c is the current loop bandwidth, ω v is the voltage loop bandwidth, G V (s)=1 / (1+s / ω v ) is the closed-loop transfer function of the voltage loop, j represents an imaginary number, C f Represents filter capacitor.

[0039] Further: S2 includes:

[0040] S21. Construct an interconnected system model for the converter model and determine the impedance Z of the interconnected system model. Σ , whose expression is:

[0041]

[0042] Among them, Z g Indicates the impedance of the power grid;

[0043] S22, impedance Z according to the interconnection system model Σ , solve the modal eigenvalue of the system on the complex plane, and its expression is:

[0044] det(Z Σ (λ))=0

[0045] Among them, λ is a modal eigenvalue of the system, and det(.) means solving the determinant.

[0046] Further: In S3, the method for locating the key dominant control loop affecting the stability of the system is: taking the modal eigenvalue with the largest real part among the modal eigenvalues ​​of the system as the mode that dominates the stability performance of the system, and the control loop corresponding to the mode that dominates the stability performance of the system as the key dominant control loop.

[0047] Further: S4 includes:

[0048] S41. Extract the key dominant control loop and regard it as an equivalent impedance Z c , considering the rest of the system as an equivalent impedance Z rest ;

[0049] S42. Determine the equivalent impedance Z c With the equivalent impedance Z rest The relationship is expressed as:

[0050]

[0051] Where Λ1 and Λ2 represent the equivalent impedance Z c With the equivalent impedance Z rest The frequency domain eigenvalue of the back-ratio matrix, eig(.) represents the operation of solving the eigenvalue function, z v Represents the equivalent impedance Z c Approximately symmetrical impedance at different frequency bands;

[0052] S43, change the control parameters in the key dominant control loop, and observe z v The phase change of the impedance of the rest of the system at the gain crossover frequency is used to complete the interaction analysis.

[0053] The beneficial effects of the present invention are:

[0054] 1. The method of the present invention makes the control loops of the grid-following converter and the grid-forming converter equivalent to the parallel admittance form, thereby realizing the analysis of the interaction between the control loops of the units from the circuit perspective, making it easier to analyze the stability of the interconnected systems;

[0055] 2. This method is also applicable to the analysis of control interaction resonance among multiple units, which improves its universality;

[0056] 3. The analysis of the oscillation mechanism of the interconnected system can take into account the combined impact of multiple controls. This method has the ability to consider multiple controls simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 A flow chart of the analysis method for the control interaction effects of the converter model;

[0058] Figure 2 A schematic diagram of an interconnection system in an embodiment;

[0059] Figure 3 Schematic diagram of system characteristic values ​​before and after the grid-connected grid-type converter under a weak power grid in the embodiment;

[0060] Figure 4 Schematic diagram of parameter sensitivity corresponding to the instability mode in the embodiment;

[0061] Figure 5 is a Bode diagram of the subsystem as the inner loop current control bandwidth of the grid-type converter changes in the embodiment;

[0062] Figure 6 1 is a Bode diagram of the subsystem as the voltage control bandwidth of the inner loop of the grid-type converter changes in the embodiment. DETAILED DESCRIPTION

[0063] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0064] like Figure 1 As shown, in one embodiment of the present invention, a method for analyzing the control interaction effect of a converter model is provided, comprising:

[0065] S1. Constructing a converter model including a control-admittance model of a grid-following converter and a control-impedance model of a grid-building converter;

[0066] S2. Construct an interconnected system model about the converter model and solve the modal eigenvalues ​​of the system;

[0067] S3. Locate the key dominant control loop based on the modal eigenvalues ​​of the system;

[0068] S4. Extract the key dominant control loop, analyze the interaction mechanism between the dominant control loop and the rest of the system, and complete the interaction impact analysis.

[0069] In S1, the converter model is equivalent to a controlled voltage source with mixed voltage and current control, and the overall dq domain admittance of the converter model is for:

[0070]

[0071] Among them, I is the 2×2 identity matrix, G I (s) and G II (s) are all controlled coefficients, Z f and Y Cf Respectively represent the filter inductance L f and capacitor C f The dq domain impedance and admittance are expressed as follows:

[0072]

[0073]

[0074] Where s is the Laplace operator, ω0 is the fundamental angular frequency of the system, and ω0 = 2π × 50, R f is the filter resistor, L f For the filter inductor.

[0075] For grid-following and grid-forming converters, calculate the controlled coefficient G I (s) and GII (s) and substitute it into the above formula to get the corresponding impedance model.

[0076] For the control-admittance model of the grid-following converter, the outer loop adopts fixed active power control, and the inner loop adopts dq decoupled current control;

[0077] Determine the sequence impedance Z corresponding to the control-admittance model of the grid-type converter GFL The methods include:

[0078] S101. According to the characteristics of the control-admittance model of the grid-following converter, the corresponding controlled coefficient is calculated, and its expression is:

[0079]

[0080]

[0081] Among them, V cd0 and I cd0 are the voltage and current values ​​of the converter in steady state, represents the transfer function of the inner loop current PI control; represents the transfer function of the outer loop active power PI control; and are the proportional parameter and integral parameter of current control respectively, and They are the proportional parameter and integral parameter of active power control respectively;

[0082] S102, according to the controlled coefficient of the control-admittance model of the grid-following converter, calculate the corresponding sequence impedance Z GFL , whose expression is:

[0083]

[0084] Among them, G P , G PLL and G C They are the closed-loop transfer functions of active power control, PLL control and current control respectively.

[0085] Specifically, the controlled coefficient G I (s) and G II (s) Substitution The corresponding expression is:

[0086]

[0087] in, is the admittance of the grid-following converter, Y Cf is the filter capacitor admittance, G PLL (s) is the transfer function of PLL;

[0088] The closed-loop transfer functions corresponding to the outer loop active power control and inner loop current control of the control-admittance model of the grid-following converter can be expressed as:

[0089]

[0090] Further considering the PI parameter setting method: So G C =1 / (1+s / ω c ),ω c is the current loop bandwidth; So G P =1 / (1+s / ω P ),ω P is the active loop bandwidth.

[0091] then It can be further simplified as:

[0092]

[0093] The corresponding sequence impedance is:

[0094] Y GFL =y P A L1 +y PLL A L2

[0095] in, Δθ GFL is the phase angle difference between the local reference coordinate system of the grid-following converter and the global reference coordinate system of the system.

[0096] For the control-impedance model of the grid-type converter, the outer loop adopts constant dq voltage decoupling control, the inner loop adopts constant dq current decoupling control, and the synchronous control loop adopts virtual synchronous generator control;

[0097] Determine the sequence impedance Z corresponding to the control-impedance model of the grid-connected converter GFM The methods include:

[0098] S111. According to the characteristics of the control-impedance model of the grid-connected converter, the corresponding controlled coefficient is calculated, and its expression is:

[0099]

[0100]

[0101] in, The transfer function of the outer loop voltage PI control is, represents the transfer function of the virtual synchronous generator control; J is the virtual inertia parameter, D p is the virtual damping parameter;

[0102] S112. Calculate the corresponding sequence impedance Z according to the controlled coefficient of the control-impedance model of the grid-type converter GFL , whose expression is:

[0103]

[0104]

[0105]

[0106] Among them, Δθ GFM is the phase angle difference between the local reference coordinate system of the control-impedance model of the grid-type converter and the global reference coordinate system of the system, ω c is the current loop bandwidth, ω v is the voltage loop bandwidth, G V (s)=1 / (1+s / ω v ) is the closed-loop transfer function of the voltage loop.

[0107] Specifically, since the grid-type converter as a whole presents a controlled voltage source characteristic to the outside, its corresponding impedance model for:

[0108]

[0109] in, is the transfer function of the PI control of the voltage loop, G VSG (s) is the transfer function of the virtual synchronous generator control

[0110] Further considering the PI parameter setting method: So G C (s)=1 / (1+s / ω c ),ω c is the current loop bandwidth; The closed-loop transfer function of the voltage loop is G V (s)=1 / (1+s / ω v ),ω v is the voltage loop bandwidth.

[0111] then It can be simplified as:

[0112]

[0113] in, Z GFM for The corresponding sequence impedance.

[0114] The S2 includes:

[0115] S21. Construct an interconnected system model for the converter model and determine the impedance Z of the interconnected system model. Σ , whose expression is:

[0116]

[0117] Among them, Z g Indicates the impedance of the power grid;

[0118] S22, impedance Z according to the interconnection system model Σ , solve the modal eigenvalue of the system on the complex plane, and its expression is:

[0119] det(Z Σ (λ))=0

[0120] Among them, λ is a modal eigenvalue of the system, det(.) represents solving the determinant, and all the modal eigenvalues ​​of the system can be obtained by solving the above formula on the complex plane.

[0121] In S3, the method for locating the key dominant control loop affecting the system stability is: taking the modal eigenvalue with the largest real part among the modal eigenvalues ​​of the system as the mode that dominates the stability performance of the system, and taking the control loop corresponding to the mode that dominates the stability performance of the system as the key dominant control loop.

[0122] Sensitivity S corresponding to control loop parameters a The calculation expression is:

[0123]

[0124] Among them, λ c is the key eigenvalue, i.e., the mode that dominates the stability performance of the system, α0 is the setting value of the parameter, Δα is the micro-increment corresponding to the parameter, and Δα is usually set to 1%·α0; according to S α By calculating the size of , we can get the key control loop that affects the stability of the system.

[0125] The S4 includes:

[0126] S41. Extract the key dominant control loop and regard it as an equivalent impedance Z c , considering the rest of the system as an equivalent impedance Z rest ;

[0127] S42. Determine the equivalent impedance Z cWith the equivalent impedance Z rest The relationship is expressed as:

[0128]

[0129] Where Λ1 and Λ2 represent the equivalent impedance Z c With the equivalent impedance Z rest The frequency domain eigenvalue of the back-ratio matrix, eig(.) represents the operation of solving the eigenvalue function, z v Represents the equivalent impedance Z c Approximately symmetrical impedance at different frequency bands;

[0130] S43, change the control parameters in the key dominant control loop, and observe z v The phase change of the impedance of the rest of the system at the gain crossover frequency is used to complete the interaction analysis.

[0131] In addition, if you remember

[0132] So the stability criterion of the system can be expressed as: v (s) and the impedance z of the rest of the system R (s) If the phase difference at the gain crossover frequency (i.e., the frequency point where the amplitudes are equal) is less than 180°, the system is stable; since the influence of the control loop is completely contained in z v (s), so this stability criterion can more intuitively reflect the interaction mechanism between system controls.

[0133] like Figure 2 As shown, in one embodiment of the present invention, taking the connection of a grid-following converter to a weak grid as a scenario, the influence of the subsequent connection of a grid-forming converter on the system stability is analyzed:

[0134] When only the grid-following converter is connected to the weak grid (SCR=3), and its PLL bandwidth is adjusted to 100Hz, the system modal characteristic value is as follows: Figure 2 As shown, the system has an unstable mode λ PLL =311+92Hz, the corresponding eigenvalue-parameter sensitivity analysis is as follows Figure 3 As shown. It can be seen that the PLL bandwidth ω PLL The SCR sensitivity is large, followed by the output power P of the grid-following converter. GFL .

[0135] When the grid-connected converter is connected, the system becomes stable and the PLL-dominated eigenvalue is changed from Figure 3 Medium PLL Moving to λ', it can be seen that this mode is no longer the key eigenvalue that dominates the stability of the system; according to Figure 4 Sensitive PLL in

[0136] The results of the degree analysis show that when the grid-connected converter is connected to the grid, the inner loop current control and voltage control bandwidth of the grid control are ω v For λ' PLL There is a significant influence on λ' PLL This is because the bandwidth of the power synchronization outer loop of the network control is low and cannot affect λ' PLL The corresponding frequency band is affected.

[0137] In order to further study the effect of grid-connected converters on grid-connected converters under weak grid conditions PLL The improvement mechanism of the mode is to divide the system into two subsystems at the grid connection point of the grid-connected converter, and the corresponding system loop ratio L(s) is:

[0138] L(s)=Z GFM (s)Y rest (s)

[0139] in, Z GFM (s) is the impedance of the grid-connected converter, Y rest (s) is the admittance of the rest of the system, Y Cf2 is the filter capacitor of the grid-type converter, is the overall impedance of the grid-connected converter, Z T2 and Z L2 They are the transformer impedance and line impedance corresponding to the grid-connected converter respectively.

[0140] In λ' PLL In the corresponding mid-high frequency band, there is Z GFM ≈Z VC I, so

[0141] [Λ1(s),Λ2(s)]=eig[L(s)]≈z VC eig[Y rest (s)]

[0142] Note [y R1 (s),y R2 (s)]=eig[Y rest (s)], let (i=1,2), the stability criterion of the system is: if z Ri (s) and the rest of the system z Ri (s) at the gain crossover frequency (GCF) of L(s) (i.e. z VC (s) and z RiIf the phase difference of (s) is less than 180°, the system is stable

[24] . Since the voltage loop and current loop control loop of the grid-connected converter are completely contained in z VC (s), so this stability criterion can more intuitively analyze the interaction mechanism between it and the grid-following converter.

[0143] Inner loop current control bandwidth of grid-connected converter Impact:

[0144] along with From 2π×1000rad / s to 2π×2000rad / s, the corresponding Bode diagram is as follows Figure 5 As shown, according to Figure 5 , z Ri (s) and z VC (s) There are multiple gain crossover frequencies, among which f c1 and f c2 The phase difference is large at low frequencies. c2 The corresponding low-frequency mode of the grid-type converter itself is the bandwidth of the inner loop current control of the grid-type converter. Increase, z VC The amplitude of (s) decreases, while its phase-frequency characteristic remains basically unchanged, and the gain crossing frequency f c1 The corresponding phase difference at is reduced from 100° to 86°, indicating that the system stability is enhanced;

[0145] like Further increase, z VC The amplitude of (s) is further reduced, that is, there is no gain crossover frequency, thus further increasing λ' PLL Stability of modal correspondence.

[0146] The inner loop voltage control bandwidth ω of the grid-connected converter v Impact:

[0147] With ω v From 2π×150rad / s to 2π×450rad / s, the corresponding Bode diagram is as follows Figure 6 As shown, Similarly, increasing the voltage loop bandwidth ω of the grid converter v This will also make z VC (s) decreases in magnitude, but due to ω v Order of magnitude less than Corresponding to z VC The phase-frequency characteristic at (s) will also change, making the gain crossover frequency f c1 The corresponding phase difference is further reduced, thereby improving the system stability.

[0148] Based on the above analysis, it can be seen that as the inner loop bandwidth of the grid-type converter ω v Increase, λ' PLL Modal stability is improved. Explained from the decomposed sub-impedance, in the frequency band corresponding to this mode, Z GFM ≈z VC Therefore, the increase in the inner loop bandwidth is equivalent to the reduction in the internal resistance of the voltage source corresponding to the grid-type converter, thereby improving the grid strength at the common connection point of the grid-type converter, thereby improving the λ' modal stability.

[0149] PLL

[0150] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for analyzing control interaction effects of a converter model, characterized in that: include: S1. Constructing a converter model including a control-admittance model of a grid-following converter and a control-impedance model of a grid-building converter; S2. Construct an interconnected system model about the converter model and solve the modal eigenvalues ​​of the system; S3. Locate the key dominant control loop based on the modal eigenvalues ​​of the system; S4. Extract the key dominant control loop, analyze the interaction mechanism between the dominant control loop and the rest of the system, and complete the interaction impact analysis.

2. The method for analyzing the control interaction effect of a converter model according to claim 1, characterized in that: In S1, the converter model is equivalent to a controlled voltage source with mixed voltage and current control, and the overall dq domain admittance of the converter model is for: Among them, I is the 2×2 identity matrix, G I (s) and G II (s) are all controlled coefficients, Z f and Y Cf Respectively represent the filter inductance L f and capacitor C f The dq domain impedance and admittance are expressed as follows: Where s is the Laplace operator, ω0 is the fundamental angular frequency of the system, R f is the filter resistor, L f For the filter inductor.

3. The method for analyzing the control interaction effect of a converter model according to claim 2, characterized in that: For the control-admittance model of the grid-following converter, the outer loop adopts fixed active power control and the inner loop adopts dq decoupled current control; Determine the sequence impedance Z corresponding to the control-admittance model of the grid-type converter GFL The methods include: S101. According to the characteristics of the control-admittance model of the grid-following converter, the corresponding controlled coefficient is calculated, and its expression is: Among them, V cd0 and I cd0 are the voltage and current values ​​of the converter in steady state, represents the transfer function of the inner loop current PI control; represents the transfer function of the outer loop active power PI control; and are the proportional parameter and integral parameter of current control respectively, and are the proportional parameter and integral parameter of active power control respectively; S102, according to the controlled coefficient of the control-admittance model of the grid-following converter, calculate the corresponding sequence impedance Z GFL , whose expression is: Among them, G P , G PLL and G C They are the closed-loop transfer functions of active power control, PLL control and current control respectively.

4. The method for analyzing the control interaction effect of a converter model according to claim 3, characterized in that: For the control-impedance model of the grid-connected converter, the outer loop adopts constant dq voltage decoupling control, the inner loop adopts constant dq current decoupling control, and the synchronous control loop adopts virtual synchronous generator control; Determine the sequence impedance Z corresponding to the control-impedance model of the grid-connected converter GFM The methods include: S111. According to the characteristics of the control-impedance model of the grid-connected converter, the corresponding controlled coefficient is calculated, and its expression is: in, The transfer function of the outer loop voltage PI control is, represents the transfer function of the virtual synchronous generator control; J is the virtual inertia parameter, D p is the virtual damping parameter; S112. Calculate the corresponding sequence impedance Z according to the controlled coefficient of the control-impedance model of the grid-type converter GFL , whose expression is: Among them, Δθ GFM is the phase angle difference between the local reference coordinate system of the control-impedance model of the grid-type converter and the global reference coordinate system of the system, ω c is the current loop bandwidth, ω v is the voltage loop bandwidth, G V (s)=1 / (1+s / ω v ) is the closed-loop transfer function of the voltage loop, j represents an imaginary number, C f Represents filter capacitor.

5. The method for analyzing the control interaction effect of a converter model according to claim 4, characterized in that: The S2 includes: S21. Construct an interconnected system model for the converter model and determine the impedance Z of the interconnected system model. Σ , whose expression is: Among them, Z g Indicates the impedance of the power grid; S22, impedance Z according to the interconnection system model Σ , solve the modal eigenvalue of the system on the complex plane, and its expression is: det(Z Σ (λ))=0 Among them, λ is a modal eigenvalue of the system, and det(.) means solving the determinant.

6. The method for analyzing the control interaction effect of a converter model according to claim 1, characterized in that: In S3, the method for locating the key dominant control loop affecting the system stability is: taking the modal eigenvalue with the largest real part among the modal eigenvalues ​​of the system as the mode that dominates the stability performance of the system, and taking the control loop corresponding to the mode that dominates the stability performance of the system as the key dominant control loop.

7. The method for analyzing control interaction effects of a converter model according to claim 1, characterized in that: The S4 includes: S41. Extract the key dominant control loop and regard it as an equivalent impedance Z c , considering the rest of the system as an equivalent impedance Z rest ; S42. Determine the equivalent impedance Z c And the equivalent impedance Z rest The relationship is expressed as: Where Λ1 and Λ2 represent the equivalent impedance Z c And the equivalent impedance Z rest The frequency domain eigenvalue of the back-ratio matrix, eig(.) represents the operation of solving the eigenvalue function, z v Represents the equivalent impedance Z c Approximately symmetrical impedance at different frequency bands; S43, change the control parameters in the key dominant control loop, and observe z v The phase change of the impedance of the rest of the system at the gain crossover frequency is used to complete the interaction analysis.

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