A method for multiple-input multiple-output frequency coupled admittance modeling of a wind turbine

Abstract

The application provides a kind of multi-input multi-output frequency coupling admittance modeling method of grid-connected wind turbine, belong to large-scale grid-connected type and grid-constructed type wind turbine frequency coupling admittance modeling technical field.The technical problem that lack of accurate small signal modeling and analysis method of grid-connected type GFL and grid-constructed type GFM doubly-fed wind turbine hybrid system in wind farm is solved.The technical scheme is as follows: including the following steps: S1, the open-loop doubly-fed motor itself admittance considering the dynamic of stator and rotor flux linkage is established;S2, the frequency domain multi-input multi-output admittance of grid-connected type and grid-constructed type doubly-fed wind turbine is obtained;S3 the unified multi-input multi-output admittance frequency domain model of closed-loop interconnection system is formed, which contains the admittance Y GFL of grid-connected type doubly-fed wind turbine and the admittance Y GFM of grid-constructed type doubly-fed wind turbine;S4, quantitative evaluation of phase-locked loop parameters and virtual synchronous control parameters.The application realizes accurate determination of frequency coupling oscillation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large-scale grid-following and grid-forming wind turbine frequency coupling admittance modeling, and particularly relates to a multi-input multi-output frequency coupling admittance modeling method for grid-following and grid-forming wind turbines. BACKGROUND

[0002] With the rapid development of high-proportion renewable energy power systems, doubly fed induction generators (DFIG) have become the mainstream model of wind power grid connection due to their flexible power control capability and cost advantage; however, in a weak grid scenario, the traditional grid-following (GFL) doubly fed wind turbine is prone to be affected by grid disturbances due to its dependence on grid voltage phase to achieve synchronization, resulting in sub-synchronous oscillation, insufficient inertia support and other stability problems. Therefore, grid-forming control doubly fed wind turbines have emerged as the times require. The grid-forming (GFM) control strategy actively provides voltage and frequency support by simulating the external characteristics of synchronous generators, and has become an important technical direction to improve system stability. Typical grid-forming control includes direct current voltage self-synchronization control, virtual oscillator control, droop control and virtual synchronous generator (VSG) control.

[0003] By comparing and analyzing the grid-forming and grid-following control of doubly fed wind turbines, it is found that the grid-forming control of the machine side of the wind turbine has better stability and adaptability when responding to various grid disturbances. At present, the small-signal modeling of wind turbines containing grid-following and grid-forming wind turbines has a method based on open-loop modal resonance, and also includes an additional damping controller design method based on normal matrix. In an extremely weak grid, the grid-following type and the grid-forming type wind turbine, the PLL part of the grid-following type is more sensitive to the strength of the grid, and the synchronization part of the grid-forming type wind turbine may also be coupled with the grid admittance in the low frequency range. The existing research mainly uses single-port or double-port equivalent models, which are not sufficient to uniformly describe the coupling relationship between the grid-following and grid-forming wind turbines and the extremely weak grid. In addition, the admittance characteristics of the hybrid system in different frequency ranges under an extremely weak grid are not clear, and the frequency coupling admittance characteristics of the grid-following and grid-forming wind turbines and the influence of various parameters on the stability of the system cannot be characterized.

[0004] How to solve the above technical problems is the problem faced by the present application. SUMMARY

[0005] In view of the technical problem that there is no accurate small signal modeling and analysis method for the grid-following (GFL) and grid-forming (GFM) doubly-fed wind turbine hybrid system in a wind farm, the application provides a multi-input multi-output frequency coupling admittance modeling method for grid-following and grid-forming wind turbines, for the first time, a multi-input multi-output (MIMO) frequency coupling admittance model is established in the dq coordinate system, which simultaneously fuses the multi-loop coupling effect of the stator and rotor flux linkage dynamics, pulse width modulation (PWM) delay, phase-locked loop (PLL) and grid-forming virtual synchronous machine (VSG) control, power outer loop and current inner loop, and significantly improves the small signal modeling accuracy of the system; based on the model, the quantitative mapping law of key parameters (such as PLL proportional coefficient, VSG virtual inertia / reactive inertia) and stability is quantitatively revealed, and the generalized Nyquist criterion and frequency domain eigenvalue trajectory analysis method are innovatively applied to realize accurate determination of frequency coupling oscillation, and provide theoretical tools and engineering practice support for stability optimization of the hybrid system.

[0006] In order to achieve the above application purpose, the technical scheme adopted by the application is specifically as follows: a multi-input multi-output frequency coupling admittance modeling method for grid-following and grid-forming wind turbines, comprising the following steps:

[0007] Step one, establishing a multi-input multi-output frequency coupling admittance model of grid-following doubly-fed wind turbines:

[0008] The complete flux linkage equation and voltage equation containing the mutual inductance of the stator and rotor in the dq coordinate system are as follows:

[0009] (4)

[0010] In the formula, is the d-axis stator flux linkage of the wind turbine in the dq coordinate system; is the q-axis stator flux linkage of the wind turbine in the dq coordinate system; is the stator self-inductance; is the d-axis stator current of the wind turbine in the dq coordinate system; is the q-axis stator current of the wind turbine in the dq coordinate system; is the mutual inductance between the stator and the rotor; is the d-axis rotor current of the wind turbine in the dq coordinate system; is the q-axis rotor current of the wind turbine in the dq coordinate system. is the d-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the q-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the rotor self-inductance. represents the dq-axis stator voltage of the wind turbine in the dq coordinate system, which can be divided into the d-axis stator voltage and the q-axis stator voltage ; is the stator resistance of the wind turbine, represents the stator current of the wind turbine in the dq coordinate system, which can be split into the d-axis stator current and the q-axis stator current ; s is the Laplace operator, represents the stator flux of the wind turbine in the dq coordinate system, which can be split into the d-axis stator flux and the q-axis stator flux ; is the electrical angular speed of the stator. represents the rotor voltage of the wind turbine in the dq coordinate system, which can be split into the d-axis rotor voltage and the q-axis rotor voltage ; is the rotor resistance of the wind turbine; represents the rotor current of the wind turbine in the dq coordinate system, which can be split into the d-axis rotor current and the q-axis rotor current ; represents the rotor flux of the wind turbine in the dq coordinate system, which can be split into the d-axis rotor flux and the q-axis rotor flux ; represents the angle difference between the stator and the rotor, where is the electrical angular speed of the rotor; s is the Laplace operator. According to formula (4), the expression of the stator current with respect to the stator voltage and the rotor current is obtained:

[0011] (5)

[0012] wherein:

[0013] (6)

[0014] The dq coordinate system established by the actual phase angle in the system is referred to as the main circuit coordinate system, and each component is represented by the superscript "g"; the coordinate system based on the phase angle output by the phase-locked loop is referred to as the control coordinate system, and each component is represented by the superscript "c". Taking the main circuit coordinate system of the doubly-fed wind turbine as the reference, the control coordinate of the doubly-fed wind turbine is calculated to the main circuit coordinate system of the wind turbine for unified analysis, which represents the phase angle tracked by the phase-locked loop. Through linearization processing, the open-loop admittance determined only by the electromagnetic coupling of the stator and the rotor is given; a small signal disturbance of the voltage is added at the grid connection point, which is defined as follows:

[0015] (7)

[0016] wherein: is the d-axis small signal disturbance component of the voltage added at the grid connection point, is the q-axis small signal disturbance component of the voltage added at the grid connection point; The d-axis voltage of the stator current in the synchronous rotating coordinate system, The q-axis voltage of the stator current in the synchronous rotating coordinate system, the rotor voltage and the stator and rotor currents are subjected to the same disturbance processing, and after the disturbance quantity is separated, the following can be obtained:

[0017] (8)

[0018] Wherein represents the d-axis small signal disturbance component of the stator current in the dq axis; represents the q-axis small signal component of the stator current in the dq axis; represents the d-axis small signal disturbance component of the rotor voltage in the dq coordinate system, represents the q-axis small signal component of the rotor voltage in the dq coordinate system. represents the transfer function matrix of the stator voltage to the stator current, represents the transfer function matrix of the rotor voltage to the rotor current, , The open-loop double-fed motor self-admittance considering the stator and rotor flux linkage dynamics is obtained as:

[0019] (1)

[0020] When considering small signal disturbance, the rotor side converter main circuit model obtains the rotor side converter main circuit modulation voltage small signal as:

[0021] (9)

[0022] Wherein is the small signal component of the modulation voltage d-axis output by the converter main circuit, is the small signal component of the modulation voltage d-axis output by the converter main circuit. The rotor side converter inner loop small signal model is:

[0023] (10)

[0024] In the formula is the small signal component of the active power, is the small signal component of the reactive power, is the steady-state value of the stator d-axis voltage in the dq coordinate system, is the steady-state value of the stator q-axis voltage in the dq coordinate system, is the steady-state value of the stator d-axis current in the dq coordinate system, is the steady-state value of the stator q-axis current in the dq coordinate system. The rotor side converter of the double-fed wind turbine adopts the rotor current control based on the stator voltage orientation vector, is the amplitude of the stator phase voltage, then the outer loop small signal model is:

[0025] (11)

[0026] This refers to the small-signal component of the d-axis reference value of the inner loop current of the dq-axis rotor. These represent the small-signal components of the q-axis reference value of the rotor inner ring current on the dq axis, respectively. The small-signal component of the active power setpoint. This refers to the small-signal component of the reactive power setpoint; when the active power setpoint tracks the actual active power value. When the reactive power setpoint tracks the actual reactive power value The reference value of the rotor dq-axis voltage of the doubly-fed induction generator is calculated and output from the inner current loop. The rotor voltage expression based on stator voltage vector orientation control is obtained from the flux linkage equation as follows:

[0027] (12)

[0028] The small signal component of the rotor voltage setpoint along the d-axis is obtained. q-axis small signal component of rotor voltage setpoint ; This represents the small-signal component of the d-axis rotor inner ring current, as actually measured on the d-axis. These represent the small-signal components of the rotor inner ring current on the dq axis and the q-axis, respectively, as actually measured. This is the proportional gain of the rotor-side current inner loop controller. The integral coefficient of the rotor-side current inner loop controller; By using pulse width modulation (PWM), the trigger signal of the converter switch is obtained, and the converter switch is controlled to achieve decoupled control of the generator stator power, thus obtaining the phase angle small signal from the main circuit variable to the control loop variable;

[0029] (13)

[0030] in The small signal component of the phase angle output by the phase-locked loop. This is the proportional gain of the phase-locked loop. The integral coefficients of the phase-locked loop are... This represents the stable value of the stator d-axis voltage at the static operating point. n This represents the number of pole pairs in the fan motor. Let be the constant of inertia of the wind turbine rotor. After obtaining the small-signal components of the phase angle of the phase-locked loop from the main circuit variables, they are converted to the control loop through Park transform. The small-signal transfer function of the rotor current in the main circuit and the control loop is derived as follows:

[0031] (14)

[0032] in, is the inverse matrix of is the steady value of rotor q-axis voltage at static operating point, is the steady value of rotor d-axis voltage at static operating point. Considering the influence of pulse width modulation (PWM) delay, we have:

[0033] (15)

[0034] is the small-signal transfer function matrix of the modulation circuit delay link, is the delay function. From the above derivation, the equivalent input admittance of the grid-following doubly-fed wind turbine considering its own admittance and the admittance of the control loop is:

[0035] (2)

[0036] where and are the small-signal transfer function matrix of the modulation voltage of the rotor-side converter main circuit; , are the small-signal transfer function matrix of the inner loop of the rotor-side converter; are the small-signal transfer function matrix of the outer loop of the rotor-side converter; , are the small-signal transfer function matrix of the modulation circuit of the rotor-side converter; , is the small-signal transfer function matrix of the phase-locked loop, is the inverse matrix of is the small-signal transfer function matrix of the modulation circuit delay link; represents the transfer function matrix from stator voltage to stator current; represents the transfer function matrix from rotor voltage to rotor current; I is the identity matrix; is the equivalent input admittance of the grid-following doubly-fed wind turbine considering all control loops.

[0037] Step two, establish a multi-input multi-output frequency coupling admittance model of the grid-forming doubly-fed wind turbine:

[0038] The grid-forming doubly-fed wind turbine simulates the 2nd order equation of synchronous generator rotor motion through virtual synchronous machine (VSG) control, to control the active frequency P-f control loop and the reactive voltage Q- The self-synchronization of the wind turbine converter is realized by the active frequency P-f control loop to generate a virtual synchronous frequency, and the reactive voltage Q- ​​The control loop generates a virtual rotor excitation voltage, and finally the virtual frequency and the virtual rotor excitation voltage are synthesized as the rotor internal potential command of the doubly-fed motor:

[0039] (16)

[0040] In the formula: is a virtual angular frequency given value of the fan output, is a virtual angular frequency actual value of the fan output; H is the active frequency of the fan P-f is the virtual inertia constant of the control loop, is the active frequency of the fan P-f is the virtual damping constant of the control loop, is the small signal component of the active power; is the given value of the rotor virtual excitation voltage of the control circuit, is the actual value of the rotor virtual excitation voltage of the control circuit; is Q- is the virtual inertia constant of the reactive voltage control loop, is the reactive voltage Q- is the virtual damping constant of the control loop, is the small signal component of the reactive power. The small signal model is:

[0041] (17)

[0042] is the system reference angular velocity 314 / rad / s, is the system grid-connection point current steady-state operating point matrix, is the system grid-connection point voltage steady-state operating point matrix. The specific expression is shown in formula (10). Considering the influence of pulse width modulation (PWM) delay, the small signal model of the rotor voltage of the doubly-fed fan control circuit in the dq coordinate system is obtained:

[0043] (18)

[0044] wherein is a delay function, , is the switching frequency, is the phase angle small signal component generated by the grid-connection control. Through each control link of the grid-connection type fan, the equivalent input admittance considering the self-admittance and the rotor-side converter control link is obtained:

[0045] (3);

[0046] wherein , A small-signal transfer function matrix of a rotor-side converter inner ring; A small-signal transfer function matrix of a rotor-side converter grid-forming virtual active synchronous link; A small-signal transfer function matrix of a rotor-side converter grid-forming virtual reactive synchronous link; A small-signal transfer function matrix of a rotor-side converter grid-forming virtual internal potential; A small-signal transfer function matrix of a modulation circuit delay link; A transfer function matrix representing stator voltage to stator current; A transfer function matrix representing rotor voltage to rotor current; I A unit matrix.

[0047] Step three, establishment of a grid multi-input multi-output frequency coupling admittance model:

[0048] Establishment of an equivalent frequency coupling impedance of a grid side , reflecting dynamic characteristics of the grid in each frequency band, and including effects of grid impedance and other operating conditions on the admittance. The grid impedance transfer function matrix may be expressed as

[0049] (19)

[0050] Wherein is a grid line resistance, is a grid line inductance, the grid impedance transfer function matrix , is a grid angular velocity.

[0051] Compared with the prior art, the beneficial effects of the present application are:

[0052] 1. The present application first establishes a grid-following and grid-forming doubly-fed wind turbine hybrid system multi-input multi-output (MIMO) frequency coupling admittance model in the dq coordinate system, which simultaneously considers the stator and rotor flux linkage dynamics, phase-locked loop or grid-forming virtual synchronous control, power / voltage outer loop, current inner loop, pulse width modulation (PWM) delay and other multi-link coupling effects, significantly improving the small-signal modeling accuracy of the grid-following and grid-forming doubly-fed wind turbine hybrid system.

[0053] 2. The present application first quantitatively gives the quantitative mapping relationship between key parameters such as phase-locked loop proportional coefficient, virtual inertia, reactive inertia and system stability, reveals the influence law of key control parameters such as grid-following phase-locked loop proportional coefficient, grid-forming virtual inertia and reactive inertia on system admittance characteristics, and provides a theoretical basis for parameter optimization and wind turbine adaptive parameter adjustment.

[0054] 3. The application is based on the generalized Nyquist criterion, and a frequency coupling oscillation stability analysis method for the mixed system of the follow-net and network-type double-fed wind turbines is proposed by the eigenvalue trajectory of the frequency domain loop gain. The proposed admittance model has the characteristics of modularization and splicing, and the MIMO admittance matrix of the closed loop can be quickly constructed by algebraic splicing of the subsystem models in the wind farm. The stability margin under different wind turbine mixing ratios, control parameters and grid strength can be quickly evaluated in the planning and design stage, which significantly improves the efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0055] The accompanying drawings are included to provide a further understanding of the application, and constitute a part of the specification, together with the embodiments of the application, to explain the application, and do not constitute a limitation on the application.

[0056] Figure 1 It is a basic topology structure diagram of the follow-net and network-type double-fed wind turbine grid-connected system in the application, wherein, It is the a-phase voltage of the wind turbine grid-connected point in the actual system, It is the b-phase voltage, It is the c-phase voltage of the grid-connected point; It is the a-phase current of the grid-connected point, It is the b-phase current, It is the c-phase current of the grid-connected point; It is the actual a-phase current of the control coordinate system rotor, It is the b-phase current, It is the c-phase current of the grid-connected point.

[0057] Figure 2 It is an equivalent admittance model diagram of the follow-net double-fed wind turbine considering different control links in the application.

[0058] Figure 3 It is an equivalent admittance model diagram of the network-type double-fed wind turbine considering different control links in the application.

[0059] Figure 4 It is an admittance sweep verification diagram of the follow-net and network-type double-fed wind turbine in the application.

[0060] Figure 5 It is an admittance characteristic diagram of the follow-net wind turbine when the phase-locked loop proportion is different in the application.

[0061] Figure 6 It is an admittance characteristic diagram of the network-type wind turbine under different active virtual inertia constants in the application.

[0062] Figure 7 It is an admittance characteristic diagram of the network-type wind turbine under different reactive virtual inertia constants in the application.

[0063] Figure 8 It is an active power response diagram of the follow-net wind turbine when the phase-locked loop proportion is different in the application.

[0064] Figure 9 System active power response graph under different active virtual inertia constant of the network-constructed wind turbine in the application.

[0065] Figure 10 System active power response graph under different reactive virtual inertia constant of the network-constructed wind turbine in the application. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below in combination with the drawings and examples. Of course, the specific examples described here are only used to explain the application, and are not used to limit the application.

[0067] Example 1: see Figures 1 to 10 A multi-input multi-output frequency coupling admittance modeling method for network-constructed wind turbines, specifically including the following contents:

[0068] The complete flux linkage equation and voltage equation of the doubly-fed wind turbine in the synchronous rotating coordinate system are shown in the formula,

[0069] (4)

[0070] In the formula, is the d-axis stator flux linkage of the wind turbine in the dq coordinate system; is the q-axis stator flux linkage of the wind turbine in the dq coordinate system; is the stator self-inductance; is the d-axis stator current of the wind turbine in the dq coordinate system; is the q-axis stator current of the wind turbine in the dq coordinate system; is the mutual inductance between the stator and the rotor; is the d-axis rotor current of the wind turbine in the dq coordinate system; is the q-axis rotor current of the wind turbine in the dq coordinate system. is the d-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the q-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the rotor self-inductance. represents the dq-axis stator voltage of the wind turbine in the dq coordinate system, which can be split into the d-axis stator voltage and the q-axis stator voltage ; is the stator resistance of the wind turbine, represents the dq-axis stator current of the wind turbine in the dq coordinate system, which can be split into the d-axis stator current and the q-axis stator current ; s is the Laplace operator, This represents the stator flux linkage along the dq axis of the wind turbine in the dq coordinate system, which can be decomposed into the stator flux linkage along the d axis. and q-axis stator flux ; It is the electric angular velocity of the stator. This represents the rotor voltage along the dq axis of the fan in the dq coordinate system, which can be decomposed into the rotor voltage along the d axis of the fan in the dq coordinate system. and q-axis rotor voltage ; The resistance of the fan rotor; This represents the rotor current along the dq axis of the fan in the dq coordinate system, which can be decomposed into the rotor current along the d axis. and q-axis rotor current ; This represents the rotor flux linkage along the dq axis of the wind turbine in the dq coordinate system, which can be decomposed into the rotor flux linkage along the d axis. and q-axis rotor flux ; This represents the angle difference between the stator and the rotor, where It is the electric angular velocity of the rotor; s Let Laplace be the operator. According to formula (4), the expression for the stator current with respect to the stator voltage and rotor current is obtained:

[0071] (5)

[0072] in:

[0073] (6)

[0074] In a doubly-fed induction generator (DFIG) wind turbine control system, the control quantity output by the rotor converter is the rotor voltage, while the stator current directly affects the grid connection point. When the controller's influence is not considered, the stator and rotor voltages are used as input variables, and the stator current as the output variable to obtain the DFIG wind turbine admittance. The dq coordinate system established by the actual phase angles in the system is called the main circuit coordinate system, with each component denoted by the superscript "g". The coordinate system established based on the phase angles output by the phase-locked loop (PLL) is called the control coordinate system, with each component denoted by the superscript "c". Using the DFIG-side main circuit coordinate system as a reference, the DFIG-side control coordinates are uniformly analyzed under the wind turbine main circuit coordinate system, representing the phase angle tracked by the PLL. The open-loop admittance, determined solely by the electromagnetic coupling of the stator and rotor themselves, is given through linearization. A small-signal voltage disturbance is added at the grid connection point, defined as follows:

[0075] (7)

[0076] In the formula: The small d-axis disturbance component of the voltage added at the grid connection point, Add a small q-axis voltage disturbance component to the grid connection point; The d-axis voltage of the stator current in the synchronous rotating coordinate system, The q-axis voltage of the stator current in the synchronous rotating coordinate system, the rotor voltage and the stator and rotor currents are subjected to the same disturbance processing, and after separating the disturbance, the following can be obtained:

[0077] (8)

[0078] wherein represents the d-axis small-signal disturbance component of the stator current in the dq axis; represents the q-axis small-signal component of the stator current in the dq axis; represents the d-axis small-signal disturbance component of the rotor voltage in the dq coordinate system, represents the q-axis small-signal component of the rotor voltage in the dq coordinate system. represents the transfer function matrix of the stator voltage to the stator current, represents the transfer function matrix of the rotor voltage to the rotor current, , The open-loop self-admittance of the doubly-fed motor considering the dynamic of the stator and rotor flux linkage is obtained as:

[0079] (1)

[0080] Equivalent admittance model of grid-following doubly-fed wind turbine considering different control loops

[0081] Generally, the doubly-fed wind turbine is connected to the grid through a converter, and the grid-connection characteristics are mainly determined by the converter, which is determined by its control strategy. According to the difference of control mechanism, it is divided into grid-following type and grid-constructing type. Among them, the traditional grid-following control strategy is to obtain the phase angle of the voltage at the point of common coupling (PCC) through the phase-locked loop (PLL), and to keep synchronization with the grid through the double-loop control of the converter. When the doubly-fed wind turbine is in steady-state operation, the capacitor voltage fluctuation on the DC bus is very small, which can be ignored in analysis. Since the main function of the grid-side converter is to control the DC voltage, the rotor side and the grid side are isolated by the capacitor, and there is no direct connection between them, so the equivalent admittance modeling of the rotor-side converter is only analyzed. According to the main circuit model of the rotor-side converter, the small-signal rotor voltage equation is obtained as:

[0082] (9)

[0083] Similarly, the small-signal model of the inner loop of the rotor-side converter is:

[0084] (10)

[0085] wherein is the small-signal component of the active power, is the small signal component of the active power, is the steady-state value of the stator d-axis voltage in the dq coordinate system, is the steady-state value of the stator q-axis voltage in the dq coordinate system, is the steady-state value of the stator d-axis current in the dq coordinate system, is the steady-state value of the stator q-axis current in the dq coordinate system. The rotor-side converter of the doubly-fed wind turbine adopts rotor current control based on stator voltage orientation vector, is the stator phase voltage amplitude, and the outer loop small signal model is:

[0086] (11)

[0087] is the small signal component of the dq-axis rotor inner loop current d-axis reference value, respectively represent the small signal component of the dq-axis rotor inner loop current q-axis reference value; is the small signal component of the active power given value, is the small signal component of the reactive power given value; when the active given value tracks the actual active value , when the reactive given value tracks the actual reactive value , the rotor dq-axis voltage reference value of the doubly-fed motor is calculated and output by the current inner loop, and the rotor voltage expression based on stator voltage vector orientation control is obtained from the flux linkage equation as follows:

[0088] (12)

[0089] the small signal component of the d-axis rotor voltage given value is obtained , the small signal component of the q-axis rotor voltage given value is ; is the small signal component of the actual measurement of the dq-axis rotor inner loop current d-axis, respectively represent the small signal component of the actual measurement of the dq-axis rotor inner loop current q-axis; is the proportional coefficient of the rotor-side current inner loop controller, is the integral coefficient of the rotor-side current inner loop controller; The trigger signal of the converter switch is obtained through pulse width modulation (PWM), and the converter switch is controlled to realize decoupling control of the generator stator-side power, and the phase angle small signal of the main circuit variable to the control link variable is obtained.

[0090] (13)

[0091] wherein is the small signal component of the phase angle output by the phase-locked loop, is the proportional coefficient of the phase-locked loop, The integral coefficient of the phase-locked loop, The stable value of the stator d-axis voltage at the static operating point, n The number of magnetic poles of the fan motor, The moment of inertia constant of the fan rotor. After the main circuit variable obtains the small signal component of the phase angle of the phase-locked loop, it is converted to the control link through the park transformation, and the small signal transfer function of the main circuit rotor current and the control link is obtained through derivation:

[0092] (14)

[0093] Wherein, is the inverse matrix of the matrix ; The stable value of the rotor q-axis voltage at the static operating point, The stable value of the rotor d-axis voltage at the static operating point. Considering the influence of pulse width modulation (PWM) delay, there is:

[0094] (15);

[0095] The small signal transfer function matrix of the modulation circuit delay link, is a delay function. The equivalent admittance considering the admittance of the grid-connected double-fed fan itself and the control link is obtained through the above derivation, wherein E is a unit matrix.

[0096] (2)

[0097] Wherein and are the small signal transfer function matrices of the modulation voltage of the main circuit of the rotor-side converter; , are the small signal transfer function matrices of the inner loop of the rotor-side converter; are the small signal transfer function matrices of the outer loop of the rotor-side converter; , are the small signal transfer function matrices of the modulation circuit of the rotor-side converter; , The small signal transfer function matrix of the phase-locked loop, is the inverse matrix of ; The small signal transfer function matrix of the modulation circuit delay link, represents the transfer function matrix of the stator voltage to the stator current; represents the transfer function matrix of the rotor voltage to the rotor current; I is a unit matrix; The equivalent input admittance of the grid-following DFIG is considered. The equivalent admittance model block diagram of the DFIG containing different control loops is obtained as shown in Fig. 4. Figure 2

[0098] 2.3 Equivalent admittance model of grid-forming DFIG considering different control loops

[0099] Since the grid-following control generally adopts voltage and current double closed loop to realize decoupling control of dq components, the control principle has no relevance with physical motion. Without additional control, the control strategy itself has no inertia characteristic. With the decrease of system inertia level, voltage and frequency are prone to fluctuate when the system is disturbed. The traditional grid-following converter is difficult to actively support when voltage and frequency drop, which may lead to more serious grid accidents. Therefore, the grid-forming control of converter emerges as the times require.

[0100] The grid-forming control does not need to rely on PLL, but can realize synchronization with the grid through power difference flow. The control core is to simulate the characteristics of synchronous generator, and support the grid by building the relationship between frequency and active power, and between voltage and reactive power. The grid-forming DFIG simulates the 2-order equation of synchronous generator rotor motion through virtual synchronous machine (VSG) control, to realize active frequency P-f Control loop and reactive voltage Q- The control loop realizes self-synchronization of the converter, and the active frequency P-f The control loop generates virtual synchronous frequency, and the reactive voltage Q- The control loop generates virtual rotor excitation voltage, and finally the virtual frequency and virtual rotor excitation voltage are synthesized as the rotor internal potential command of the DFIG:

[0101] (16);

[0102] In the formula: is the given value of virtual angular frequency of the converter output, is the actual value of virtual angular frequency of the converter output; H is the active frequency P-f is the virtual inertia constant of the control loop, is the active frequency P-f is the virtual damping constant of the control loop, is the small signal component of active power; is the given value of virtual excitation voltage of the rotor of the control circuit, is the actual value of virtual excitation voltage of the rotor of the control circuit; is the Q- is the virtual inertia constant of the reactive voltage control loop, ​For reactive voltage Q- Virtual damping constant of control loop, For reactive power small signal component. Small signal model is:

[0103] (17);

[0104] For system reference angular velocity 314 / rad / s, Is the system grid point current steady-state operating point matrix, Is the system grid point voltage steady-state operating point matrix. The specific expression is shown in equation (10). Considering the influence of pulse width modulation (PWM) delay, the rotor voltage small signal model of the double-fed wind turbine control circuit in the dq coordinate system is obtained:

[0105] (18);

[0106] Wherein Delay function, , Switching frequency, Phase angle small signal component generated by grid forming control. Through each control link of the grid forming wind turbine, the equivalent input admittance considering its own admittance and the rotor side converter control link is obtained:

[0107] (3);

[0108] Wherein , Rotor side converter inner loop small signal transfer function matrix; Rotor side converter grid forming virtual active synchronous link small signal transfer function matrix; Rotor side converter grid forming virtual reactive synchronous link small signal transfer function matrix; Rotor side converter grid forming virtual internal potential transfer function matrix; Modulation circuit delay link small signal transfer function matrix; Indicates the transfer function matrix of stator voltage to stator current; Indicates the transfer function matrix of rotor voltage to rotor current; I Unit matrix.

[0109] Y GFL , Y GFM And the grid side equivalent admittance Y g Algebraic splicing is carried out to obtain the multi-input multi-output frequency coupling admittance matrix of the overall hybrid system, wherein the splicing process maintains the power conservation and signal flow consistency of each subsystem port variable, and forms a unified multi-input multi-output admittance frequency domain model of the closed-loop interconnected system.

[0110] Figure 4 The frequency sweep results validated the effectiveness of the proposed modeling method. It can be seen that in the dd channel, the amplitude of the admittance of the grid-fed fan (GFL) is close to that of the grid-fed fan (GFM), and the phase angle is inductive in the low-frequency band. As the frequency increases, the admittance amplitude of the grid-fed fan shows a downward "dipping" at the supersynchronous bandwidth, and the phase exhibits capacitive negative damping at the supersynchronous bandwidth. The dominant factor is the AC voltage loop introduced by the grid-fed fan (GFM). In the dq channel, the amplitude of the admittance of the grid-fed fan (GFL) is significantly higher than that of the grid-fed fan (GFM), and its phase angle is also inductive in the low-frequency band. Due to the coupling between the dq admittances, as the frequency increases, the admittance amplitude of the grid-fed fan (GFM) exhibits an alternating "dipping and bulging" phenomenon at the supersynchronous bandwidth, and the phase also shows an alternating pattern of capacitive negative damping and inductive positive damping at the supersynchronous bandwidth. In the qd channel, the DGFL admittance exhibits positive resistance characteristics, while the grid-fed fan (GFM) admittance amplitude shows capacitive characteristics in the low-frequency range, and the phase angle shows positive resistance characteristics. As the frequency increases, the grid-fed fan (GFL) admittance becomes capacitive in the high-frequency range. The GFM admittance amplitude shows a downward "dipping" phenomenon in the supersynchronous band bandwidth, and the phase exhibits capacitive negative damping in the supersynchronous band bandwidth. In the qq channel, the GFL admittance amplitude is significantly higher than the GFM admittance amplitude, and its phase angle is also inductive in the low-frequency range. As the frequency increases, the GFM admittance amplitude shows a downward "dipping" phenomenon in the supersynchronous band bandwidth, and the phase exhibits inductive positive damping in the supersynchronous band bandwidth.

[0111] Example 2: Figure 5 Indicates the phase-locked loop ratio The Bode plots of the output admittance of the grid-type wind turbine (GFL) are shown for coefficients of 1, 10, and 20. The plots show that changing the phase-locked loop (PLL) proportional gain only affects the output admittance of the dq and qq channels. The PLL proportional gain primarily affects the amplitude and phase angle of the supersynchronous band. As the proportional gain increases, the range of frequencies exhibiting negative damping within the supersynchronous band widens, indicating that the system stability deteriorates with increasing PLL proportional gain.

[0112] Figure 6 This shows the Bode plot of the output admittance of a grid-connected wind turbine (GFM) when the virtual inertia constant H of the active power element is 10, 30, and 50. Figure 6It can be seen that the virtual inertia constant H in the active link has a great influence on the output admittance amplitude and phase angle of the four channels of the grid forming fan (GFM). The main influence of H on the amplitude and phase angle of the d-d channel is mainly reflected in the subsynchronous frequency band and the super-synchronous frequency band. With the increase of H, the output admittance amplitude of the grid forming fan (GFM) in the subsynchronous frequency band and the super-synchronous frequency band gradually increases, but its positive damping frequency band in the subsynchronous frequency band becomes narrower; on the contrary with the subsynchronous frequency band, the output admittance of the d-d channel in the super-synchronous frequency band becomes wider with the increase of H. In the d-q channel, the influence of H on the output admittance is mainly reflected in the peak value and the super-synchronous frequency band. With the increase of H, the peak value of the output admittance decreases, and the negative damping in the super-synchronous frequency band becomes positive damping. When H=10, the phase angle of the output admittance is between 90° and 270°, and the amplitude of H is large, which is not conducive to the stability of the system. When H=30, the phase angle of the output admittance is between -90° and 90°, and the output admittance presents a positive damping characteristic. Unlike the d-q channel, H also has an influence on the low frequency band of the output admittance of the q-d channel. With the increase of H, the amplitude in the low frequency band increases, which improves the response speed and accuracy of the system in the low frequency band. Changing H, the amplitude in the super-synchronous frequency band appears a "concave" to varying degrees, and when H becomes larger, the degree of "concave" of the amplitude weakens. When H=10, the phase angle of the output admittance is between -180° and 0°, and its negative damping frequency band in the super-synchronous frequency band is wide, and the system is easy to be unstable; when H=30, it presents a positive damping in the super-synchronous frequency band, which is conducive to the stability of the system. H has little influence on the amplitude and phase angle of the q-q channel admittance.

[0113] Figure 7 is the virtual inertia constant of the reactive link When H is 10, 30 and 50 respectively, the output admittance Bode diagram of the grid forming fan (GFM). As can be seen from the figure, the virtual inertia constant H in the reactive link has little influence on the output admittance amplitude and phase angle of the four channels of the grid forming fan (GFM), mainly affecting the amplitude of the d-q channel, and having no influence on the phase angle. With the increase of , the amplitude of the d-q channel gradually moves up, indicating that the response speed of the system is accelerated.

[0114] ​To verify the previous analysis on the influence of the parameters of the synchronization loop on the stability of the hybrid system, a PSCAD simulation model of a wind farm system under extremely weak grid conditions was established, including grid-following and grid-forming DFIGs. At t = 5 s, a 0.1-p.u. voltage step disturbance occurred in the grid voltage. Figure 8 shows the active power and voltage responses of the hybrid system under different PLL proportional gain kPPLL settings in the grid-following DFIG when a 0.1-p.u. step disturbance occurred in the grid voltage at t = 5 s. When kPPLL is small, the system maintains stable responses in all aspects. However, when kPPLL increases from 1 to 20, the active power and voltage responses gradually deteriorate, and eventually oscillate and become unstable. These results confirm that an excessively large kPPLL value in the grid-following DFIG can impair the stability of the system under extremely weak grid conditions.

[0115] The active power and voltage responses of the hybrid system under small disturbances in the active power loop of the grid-forming DFIG were analyzed under different virtual inertia constants H, as shown in Figure 9. When H = 10, the system exhibits unstable behavior, and the power diverges after the disturbance. As H increases from 10 to 40, the overshoot, oscillation amplitude, and regulation time of the power response significantly decrease, indicating that the dynamic performance is improved and the stability is enhanced. The voltage response also exhibits a similar trend. From this result, it can be seen that increasing the value of H can significantly improve the stability of the hybrid system to some extent.

[0116] Figure 10 shows the influence of different virtual inertia constants on the active power and voltage responses of the hybrid system in the reactive power loop under small disturbances. Within the range of inertia constants from 10 to 200, the system always remains stable. Although the dynamic response of the active power slightly slows down as the inertia constant increases, the overall influence on the small-signal stability of the system is small.

[0117] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of multiple-input-multiple-output frequency- coupled admittance modeling of a wind turbine, the method comprising: The method comprises the following steps: Step S1, establishing open-loop double-fed motor self-admittance considering stator and rotor flux linkage dynamics: ；（1） wherein represents a transfer function matrix of stator voltage to stator current; represents a transfer function matrix of rotor voltage to rotor current; is the open loop doubly-fed machine self-admittance; Step S2, under the framework of main circuit coordinate system and control coordinate system, small signal modeling is respectively performed on the rotor side converter of the grid-following type and grid-forming type double-fed wind turbine and all control links thereof, to obtain the frequency domain multi-input multi-output admittance of the grid-following type and grid-forming type double-fed wind turbine respectively: The admittance model considering the self-admittance of the grid-following type double-fed wind turbine and the power outer loop, current inner loop, modulation link and time delay control link is established. ；（2） wherein and is the small-signal transfer function matrix of the rotor-side converter main circuit modulation voltage; , is the small-signal transfer function matrix of the rotor-side converter inner loop; is the small-signal transfer function matrix of the rotor-side converter outer loop; , is the small-signal transfer function matrix of the rotor-side converter modulation circuit; , is the small-signal transfer function matrix of the phase-locked loop, is the inverse matrix of ; is the small-signal transfer function matrix of the modulation circuit delay element; represents the transfer function matrix of the stator voltage to the stator current; represents the transfer function matrix of the rotor voltage to the rotor current; I is the identity matrix; is the equivalent input admittance of the grid-following doubly-fed wind turbine taking into account all control loops; Equivalent input admittance of the self-admittance of the grid-forming type double-fed wind turbine and the control link of the rotor side converter: ；（3） wherein , is the small-signal transfer function matrix of the inner ring of the rotor-side converter; is the small-signal transfer function matrix of the grid-forming virtual active power synchronous link of the rotor-side converter; is the small-signal transfer function matrix of the grid-forming virtual reactive power synchronous link of the rotor-side converter; is the small-signal transfer function matrix of the grid-forming virtual inner potential of the rotor-side converter; is the small-signal transfer function matrix of the delay link of the modulation circuit; denotes the transfer function matrix of the stator voltage to the stator current; denotes the transfer function matrix of the rotor voltage to the rotor current; I is the identity matrix; is the equivalent input admittance of the grid-forming doubly-fed wind turbine taking into account all control links; Step S3, obtaining a net-type doubly-fed wind turbine admittance Y including the admittance Y through the port connection relationship GFL and a grid-type doubly-fed wind turbine admittance Y GFM forming a unified multi-input multi-output admittance frequency domain model of the closed-loop interconnected system; Step S4, quantitatively evaluating the influence of the parameters of the phase-locked loop and the parameters of the virtual synchronous control on the admittance Y of the grid-following doubly-fed wind generator GFL and the admittance Y of the grid-forming doubly-fed wind generator GFM characteristics.

2. The method of claim 1, wherein, The step S1 comprises the following steps: S1-1: writing complete flux linkage equations and voltage equations containing stator and rotor mutual inductance in dq coordinate system: （4）； wherein is the d-axis stator flux linkage of the wind turbine in the dq coordinate system; is the q-axis stator flux linkage of the wind turbine in the dq coordinate system; is the d-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the q-axis rotor flux linkage of the wind turbine in the dq coordinate system; is the stator self-inductance; is the d-axis stator current of the wind turbine in the dq coordinate system; is the q-axis stator current of the wind turbine in the dq coordinate system; is the mutual inductance between the stator and the rotor; is the d-axis rotor current of the wind turbine in the dq coordinate system; is the q-axis rotor current of the wind turbine in the dq coordinate system; is the rotor self-inductance; denotes the dq-axis stator voltage of the wind turbine in the dq coordinate system, which is split into the d-axis stator voltage and the q-axis stator voltage ; is the stator resistance of the wind turbine, denotes the dq-axis stator current of the wind turbine in the dq coordinate system, which is split into the d-axis stator current and the q-axis stator current ; s is the Laplace operator, denotes the dq-axis stator flux linkage of the wind turbine in the dq coordinate system, which is split into the d-axis stator flux linkage and the q-axis stator flux linkage ; denotes the dq-axis rotor voltage of the wind turbine in the dq coordinate system, which is split into the d-axis rotor voltage of the wind turbine in the dq coordinate system and the q-axis rotor voltage ; is the rotor resistance of the wind turbine; denotes the dq-axis rotor current of the wind turbine in the dq coordinate system, which is split into the d-axis rotor current and the q-axis rotor current ; denotes the dq-axis rotor flux linkage of the wind turbine in the dq coordinate system, which is split into the d-axis rotor flux linkage and the q-axis rotor flux linkage ; denotes the angle difference between the stator and the rotor, is the electrical angular velocity of the stator, is the electrical angular velocity of the rotor; s is the Laplace operator; the expression of the stator current with respect to the stator voltage and the rotor current is obtained according to formula (4): （5）； Wherein: （6）； S1-2: the dq coordinate system established by the actual phase angle in the system is called the main circuit coordinate system, and each component is represented by the upper mark "g"; the coordinate system based on the phase angle output by the phase-locked loop is called the control coordinate system, and each component is represented by the upper mark "c"; the double-fed wind turbine control coordinate is calculated to the wind turbine main circuit coordinate system for unified analysis, representing the phase angle tracked by the phase-locked loop; through linearization processing, only the open-loop admittance determined by the electromagnetic coupling of the stator and the rotor is given; a small signal disturbance of voltage is added at the grid connection point, and is defined as follows: （7）； wherein: is the d-axis small signal perturbation component added to the voltage at the point of interconnection, is the q-axis small signal perturbation component added to the voltage at the point of interconnection; is the steady state voltage of the stator d-axis in the synchronous rotating coordinate system, is the steady state voltage of the stator q-axis in the synchronous rotating coordinate system, and the perturbation is made to the rotor voltage and the stator and rotor currents, and after separating the perturbation, （8）； wherein represents the d-axis small-signal perturbation component of the stator current on the dq-axes; represents the q-axis small-signal component of the stator current on the dq-axes; represents the d-axis small-signal perturbation component of the rotor voltage in the dq-axes, represents the q-axis small-signal component of the rotor voltage in the dq-axes; represents the transfer function matrix of the stator voltage to the stator current, represents the transfer function matrix of the rotor voltage to the rotor current, , the open-loop doubly-fed machine self-admittance taking into account the stator and rotor flux linkage dynamics is obtained as: （1）。 3. The method of claim 1, wherein, The step S2 comprises the following steps: S2-1: for the wind turbine: establish the phase-locked loop small signal model, the rotor current inner loop small signal model, the power outer loop small signal model, and count in the pulse width modulation PWM delay link to form the equivalent multi-input multi-output admittance Y of the wind turbine GFL According to the rotor-side converter main circuit model, the rotor-side converter main circuit modulation voltage small signal is: （9）； wherein is a small signal component of the modulation voltage d-axis output by the converter main circuit, is a small signal component of the modulation voltage d-axis output by the converter main circuit, the inner loop small signal model of the rotor side converter is （10）； wherein is a small signal component of the active power, is a small signal component of the reactive power, is a steady state value of the stator d-axis voltage in the dq coordinate system, is a steady state value of the stator q-axis voltage in the dq coordinate system, is a steady state value of the stator d-axis current in the dq coordinate system, is a steady state value of the stator q-axis current in the dq coordinate system, the rotor side converter of the doubly-fed wind turbine employs a rotor current control based on stator voltage oriented vector, is the stator phase voltage amplitude, then the outer loop small signal model is: （11）； is a small signal component of the dq-axis rotor inner loop current d-axis reference value, is a small signal component of the dq-axis rotor inner loop current q-axis reference value, respectively; is a small signal component of the active power given value, is a small signal component of the reactive power given value; when the active given value tracks the active actual value , when the reactive given value tracks the reactive actual value The rotor dq-axis voltage reference value of the doubly-fed motor is calculated by the current inner loop, and the rotor voltage expression based on the stator voltage vector orientation control is obtained from the flux linkage equation as follows: （12）； a small signal component of the d-axis of the rotor voltage command value a small signal component of the q-axis of the rotor voltage command value ; a small signal component of the d-axis of the actual measurement of the dq-axis rotor inner loop current, a small signal component of the q-axis of the actual measurement of the dq-axis rotor inner loop current, respectively; a proportional coefficient of the rotor-side current inner loop controller, an integral coefficient of the rotor-side current inner loop controller; a trigger signal of the converter switch is obtained through pulse width modulation (PWM), the converter switch is controlled to realize decoupling control of the generator stator-side power, and a phase angle small signal of a main circuit variable to a control link variable is obtained. （13）； wherein is a small signal component of the phase angle output by the phase-locked loop, is a proportional coefficient of the phase-locked loop, is an integral coefficient of the phase-locked loop, is a stable value of the stator d-axis voltage at a static operating point, n is the number of magnetic poles of the fan motor, is a rotor moment of inertia constant of the fan; after the main circuit variable obtains a small signal component of the phase angle output by the phase-locked loop, the small signal component is converted to a control link through a park conversion, and a small signal transfer function of the main circuit rotor current and the control link is obtained through derivation: （14）； wherein is the inverse matrix of the matrix ; a stable value of the rotor q-axis voltage at the static operating point, a stable value of the rotor d-axis voltage at the static operating point; taking into account the influence of the pulse width modulation (PWM) delay, then （15）； The small-signal transfer function matrix of the modulation circuit delay element, is the delay function; the derivation takes into account the equivalent admittance of the control loop and the admittance of the doubly-fed wind turbine itself: （2）； wherein and is a small signal transfer function matrix of the rotor side converter main circuit modulation voltage; , is a small signal transfer function matrix of the rotor side converter inner loop; is a small signal transfer function matrix of the rotor side converter outer loop; , is a small signal transfer function matrix of the rotor side converter modulation circuit; , is a small signal transfer function matrix of the phase locked loop, is an inverse matrix of; is a small signal transfer function matrix of the modulation circuit delay element; represents a transfer function matrix of the stator voltage to the stator current; represents a transfer function matrix of the rotor voltage to the rotor current; I is an identity matrix; is an equivalent input admittance of the grid-following doubly-fed wind turbine considering all control loops; S2-2: for network type wind turbine, establish small signal model of virtual synchronous generator second order swing equation, active frequency P-f control link, reactive voltage Q- control link, voltage outer loop small signal model, form network type wind turbine equivalent multi-input multi-output admittance Y GFM ; The network-constructed doubly-fed wind turbine controls a second-order equation simulating the rotor motion of a synchronous generator by a virtual synchronous generator (VSG) to base the active frequency P-f Control loop and reactive voltage Q- The control loop realizes self-synchronization of the wind turbine converter, by the active frequency P-f The control loop generates a virtual synchronous frequency, by the reactive voltage Q- The control loop generates a virtual rotor excitation voltage, and finally synthesizes the virtual synchronous frequency and the virtual rotor excitation voltage as the rotor internal potential command of the doubly-fed machine: （16）； where: ωg is the virtual angular frequency of the fan output given value, ωg is the virtual angular frequency of the fan output actual value; H ωg is the fan active frequency P-f virtual inertia constant of the control loop, ωg is the fan active frequency P-f virtual damping constant of the control loop, ωg is the active power small signal component; ωg is the given value of the virtual excitation voltage of the control circuit rotor, ωg is the actual value of the virtual excitation voltage of the control circuit rotor; ωg is the Q- virtual inertia constant of the reactive voltage control loop, ωg is the reactive voltage Q- virtual damping constant of the control loop, ωg is the reactive power small signal component; small signal model: （17）； is the system reference angular velocity 314 / rad / s, is the system grid point current steady state operating point matrix, is the system grid point voltage steady state operating point matrix, considering the influence of pulse width modulation (PWM) delay, the rotor voltage small signal model of the double-fed wind turbine control circuit in the dq coordinate system is obtained: （18）； wherein is a time delay function, , is a switching frequency, The phase angle small signal component generated by grid forming control is considered by each control loop of the grid forming wind turbine, and the equivalent input admittance of the rotor side converter control loop and the rotor side admittance are considered. （3）； wherein , is the small-signal transfer function matrix of the inner ring of the rotor-side converter; is the small-signal transfer function matrix of the virtual active power synchronous link of the rotor-side converter grid-forming; is the small-signal transfer function matrix of the virtual reactive power synchronous link of the rotor-side converter grid-forming; is the small-signal transfer function matrix of the virtual inner potential of the rotor-side converter grid-forming; is the small-signal transfer function matrix of the delay link of the modulation circuit; denotes the transfer function matrix of the stator voltage to the stator current; denotes the transfer function matrix of the rotor voltage to the rotor current; I is the identity matrix.

4. The method of claim 1, wherein, The step S3 comprises the following steps: S3-1 : Establishing the equivalent frequency coupled admittance Y of the grid side g The grid impedance transfer function matrix is represented as: （19）； wherein is the grid line resistance, is the grid line inductance, the grid impedance transfer function matrix , is the grid angular velocity; S3-2: Through the port connection relationship, the network fan admittance Y GFL and the network fan admittance Y GFM Perform algebraic splicing to obtain a multi-input multi-output frequency coupling admittance matrix of the overall hybrid system, wherein the splicing process maintains the power conservation and signal flow consistency of the port variables of each subsystem, forming a unified multi-input multi-output admittance frequency domain model of the closed-loop interconnection system.

5. The method of claim 1, wherein, The step S4 comprises the following steps: S4-1: respectively to the proportional coefficient kP of the phase-locked loop PLL Parameter perturbation, integral coefficient ki PLL Parameter perturbation, output amplitude-phase-frequency response curve of each element in the admittance matrix, quantify the proportional coefficient kP of the phase-locked loop PLL And integral coefficient ki PLL The influence law of the phase-locked loop bandwidth and phase margin; S4-2: Parameter perturbation on virtual inertia coefficient of virtual synchronous link H , virtual damping coefficient, quantifying the influence law of virtual synchronous parameters on inertia characteristics, damping characteristics and frequency coupling strength of the system. S4-3: according to the analysis of the phase-locked loop coefficient and the virtual inertia link coefficient, the control parameter range of each link is determined.

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