Method and device for suppressing torsional vibration of shaft system of constructed net type doubly-fed fan at variable wind speed

Abstract

The invention discloses a method and device for restraining shaft system torsional vibration of a net-forming type double-fed fan under the variable wind speed. The method comprises the steps that a mathematical model of the electromagnetic torque-rotating speed difference of the net-forming type double-fed fan is constructed; drawing an electromagnetic torque-rotating speed difference Bode diagram according to the mathematical model; according to the mechanical parameters of the wind turbine and the motor, the shafting natural oscillation frequency of the doubly-fed fan is calculated, and stability analysis is conducted on damping of the shafting natural oscillation frequency in combination with the Bode diagram; drawing a small-signal model block diagram according to the mathematical model; analyzing the small-signal model block diagram to obtain an analysis result that a current loop provides a coupling path for the rotating speed and the active power; according to a stability analysis result and an analysis result of the small-signal model block diagram, negative damping brought by an operation area is weakened by reducing current loop bandwidth, so that the risk of torsional vibration of the shaft system is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of wind power generation control, and particularly to a method and device for suppressing shaft torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speeds. Background Art

[0002] In recent years, the development of doubly-fed wind power has been rapid, and the installed capacity has continued to grow rapidly.

[0003] In order to improve the stability of a wind power generation system based on a doubly-fed induction generator (DFIG) operating under a weak grid and its active support ability, the DFIG with grid-forming (GFM) control has received extensive attention. The control structure of the GFM-DFIG determines that its mechanical and electrical systems have strong coupling in the low-frequency range, so shaft torsional vibration is likely to occur.

[0004] Currently, the following research has been carried out on the shaft torsional vibration problem of grid-forming doubly-fed wind turbines at home and abroad: (1) Grid-forming doubly-fed wind turbines are more likely to have shaft torsional vibration than grid-following control due to their lower active loop bandwidth; (2) Control strategies of differential feedforward compensation and torque feedback compensation have been proposed to suppress the shaft torsional vibration of grid-forming doubly-fed wind turbines; (3) The shaft torsional vibration of a doubly-fed wind turbine using hybrid synchronous control has been analyzed, and it has been pointed out that increasing the hybrid synchronous coefficient can suppress the shaft torsional vibration.

[0005] In summary, the above research only analyzes the torsional vibration characteristics of grid-forming doubly-fed wind turbines under constant wind speeds, and usually introduces dampers to improve their shaft characteristics. However, on the one hand, due to the volatility of wind speeds in actual working conditions, the wind turbine will operate in different operating regions; on the other hand, the external damper controller will change the grid-forming control performance. Therefore, it is difficult for traditional methods to improve the grid connection stability of grid-forming doubly-fed wind turbines under variable wind speed conditions without changing the grid-forming control performance. Summary of the Invention

[0006] In view of this, the present invention provides a method and device for suppressing shaft torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speeds, which solves the problem of relatively limited scope of action of traditional methods by reducing the current loop bandwidth, and provides a reference for improving the grid connection stability of grid-forming doubly-fed wind turbines.

[0007] According to the first aspect of the embodiments of the present application, a method for suppressing shaft torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speeds is provided, including:

[0008] Construct a mathematical model of the electromagnetic torque - speed difference of the grid-forming doubly-fed wind turbine;

[0009] According to the mathematical model, draw a Bode diagram of the electromagnetic torque - speed difference;

[0010] Calculate the natural oscillation frequency of the shafting of the doubly-fed wind turbine according to the mechanical parameters of the wind turbine and the motor, and perform a stability analysis on the damping of the natural oscillation frequency of the shafting in combination with the Bode diagram;

[0011] Draw a small-signal model block diagram according to the mathematical model;

[0012] Analyze the small-signal model block diagram to obtain the analysis result that the current loop provides a coupling path for the rotational speed and the active power;

[0013] According to the stability analysis result and the analysis result of the small-signal model block diagram, weaken the negative damping brought by the operating region by reducing the current loop bandwidth, thereby reducing the risk of shafting torsional vibration.

[0014] According to the second aspect of the embodiments of the present application, there is provided a device for suppressing shafting torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speeds, including:

[0015] A construction module for constructing a mathematical model of the electromagnetic torque - rotational speed difference of the grid-forming doubly-fed wind turbine;

[0016] A first drawing module for drawing a Bode diagram of the electromagnetic torque - rotational speed difference according to the mathematical model;

[0017] A calculation and analysis module for calculating the natural oscillation frequency of the shafting of the doubly-fed wind turbine according to the mechanical parameters of the wind turbine and the motor, and performing a stability analysis on the damping of the natural oscillation frequency of the shafting in combination with the Bode diagram;

[0018] A second drawing module for drawing a small-signal model block diagram according to the mathematical model;

[0019] An analysis module for analyzing the small-signal model block diagram to obtain the analysis result that the current loop provides a coupling path for the rotational speed and the active power;

[0020] A suppression module for weakening the negative damping brought by the operating region by reducing the current loop bandwidth according to the stability analysis result and the analysis result of the small-signal model block diagram, thereby reducing the risk of shafting torsional vibration.

[0021] According to the second aspect of the embodiments of the present application, there is provided an electronic device, including:

[0022] One or more processors;

[0023] A memory for storing one or more programs;

[0024] When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0025] The technical solution provided by the embodiments of the present application may include the following beneficial effects:

[0026] Construct a mathematical model of the electromagnetic torque - speed difference of a grid-forming doubly-fed wind turbine; draw a Bode diagram of the electromagnetic torque - speed difference according to the mathematical model; calculate the natural oscillation frequency of the shafting of the doubly-fed wind turbine based on the mechanical parameters of the wind turbine and the motor, and perform a stability analysis on the damping of the natural oscillation frequency of the shafting in combination with the Bode diagram; draw a small-signal model block diagram according to the mathematical model; analyze the small-signal model block diagram to obtain the analysis result that the current loop provides a coupling path for the speed and active power; according to the stability analysis result and the analysis result of the small-signal model block diagram, weaken the negative damping brought by the operating region by reducing the current loop bandwidth, so as to change the damping characteristics of the shafting of the doubly-fed wind turbine in different operating regions, thereby reducing the risk of shafting torsional vibration. Since there are positive and negative differences in the speed loop in different operating regions, this method can take into account the stability of both operating regions at the same time, weaken the negative damping generated during the switching process of the grid-forming doubly-fed wind turbine in the operating region, and thus reduce the risk of shafting torsional vibration.

[0027] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0029] Figure 1 is a flowchart of a method for suppressing shafting torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speed shown according to an exemplary embodiment.

[0030] Figure 2 is a schematic diagram of the grid-connected operation of a grid-forming doubly-fed wind turbine provided by an embodiment of the present invention.

[0031] Figure 3 is a phase-frequency characteristic diagram of the electromagnetic torque and speed difference corresponding to different operating regions provided by an embodiment of the present invention.

[0032] Figure 4 The small-signal structure diagram of the electromagnetic torque and speed difference of the grid-forming doubly-fed wind turbine provided by an embodiment of the present invention.

[0033] Figure 5 is a simplified analysis diagram of the small-signal of the electromagnetic torque and speed difference provided by an example of the present invention.

[0034] Figure 6 is an amplitude-frequency characteristic diagram of branch 1 under different current loop bandwidths provided by an embodiment of the present invention.

[0035] Figure 7It is the phase angle difference diagram under different operating regions with different current loop bandwidths provided by the embodiments of the present invention.

[0036] Figure 8 It is a block diagram of a device for suppressing shaft torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speed shown according to an exemplary embodiment.

[0037] Figure 9 It is a block diagram of an electronic device shown according to an exemplary embodiment. Detailed implementation manners

[0038] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0039] The terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "the", and "said" used in the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0040] Figure 1 It is a flowchart of a method for suppressing shaft torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speed shown according to an exemplary embodiment. As Figure 1 shown, the method may include the following steps:

[0041] S1: Construct a mathematical model of the electromagnetic torque - speed difference of the grid-forming doubly-fed wind turbine. This step may include the following sub-steps:

[0042] S11: Establish a first small-signal transfer model considering the mechanical transmission system link and the speed control link according to the characteristics of the wind turbine in front of the doubly-fed wind turbine;

[0043] Specifically, according to Figure 2 , the first small-signal transfer model is as follows:

[0044] Mechanical transmission system link: ;

[0045] Speed control link: ;

[0046] Where, Δ represents the small-signal quantity of the variable; H t 、H gare the equivalent wind turbine inertia and the equivalent motor inertia; T m 、T 12 、T e are the mechanical torque input to the wind turbine, the torque of the drive shaft, and the electromagnetic torque input to the motor; ω t and ω r are the rotational speed of the wind turbine and the rotational speed of the generator respectively; θ Δ and ω Δ are the angular displacement and the speed difference of the wind turbine relative to the rotor of the doubly-fed wind turbine respectively; K m and D m are the mechanical stiffness coefficient and the mechanical damping coefficient; P ref represents the active power command set value, and G7 is the rotational speed - power command change matrix; k opt represents a constant related to the wind turbine, and ω t0 is the rotational speed of the wind turbine during the steady-state operation of the wind turbine; H ω represents the rotational speed controller.

[0047] S12: According to the electrical control characteristics of the doubly-fed wind turbine, establish a second small-signal transfer model considering the doubly-fed wind turbine model, the voltage outer-loop control link, and the current control inner-loop link;

[0048] Specifically, according to Figure 2 , the second small-signal transfer model is shown as follows respectively:

[0049] Doubly-fed wind turbine model: ;

[0050] Voltage outer-loop control link: ;

[0051] Current inner-loop control link: ;

[0052] Among them, Δ represents the small-signal quantity of the variable; U sdq 、I sdq 、U rdq 、I rdq are the dq-axis components of the stator voltage and current and the rotor voltage and current of the doubly-fed wind turbine respectively; s is the Laplace operator; ω1 is the power frequency angular frequency; R s 、R r 、L s 、L r 、L m are the stator and rotor resistances, the stator and rotor inductances, and the mutual inductance respectively; ω s is the slip angular frequency; ψ rd0 、ψ rd0 are the d-axis and q-axis steady-state values of the rotor flux linkage respectively; G 0_1 and G 0_2 are the stator current - stator voltage change matrix and the rotor current - stator voltage change matrix respectively; G0_3 , G 0_4 and G 0_5 are the stator current - rotor voltage change matrix, rotor current - rotor voltage change matrix, and speed - rotor voltage change matrix respectively; G 2_0 and G 2_1 are the coefficient change matrices caused by control respectively, G 2_3 and G 2_4 are the voltage loop and current loop controllers; the superscript "ref" represents the command value of the corresponding variable; θ and E are the power synchronization generation angle and the voltage loop amplitude given value respectively; the superscript "s" represents the variable in the actual coordinate system; the superscript "c" represents the variable in the control coordinate system.

[0053] S13: According to the topology of the grid - forming doubly - fed wind turbine, establish the third - order small - signal transfer models of the coordinate transformation link, power calculation link, power control link, and power - torque link;

[0054] Specifically, according to Figure 2 , when some control links are linearized, mathematical models need to be supplemented to make the control equations hold. Therefore, the third - order small - signal transfer models of the coordinate transformation link, power calculation link, power control link, and power - torque link are established as follows:

[0055] Coordinate transformation link: ;

[0056] Power calculation link: ;

[0057] Power control link: ;

[0058] Power - torque model: ;

[0059] Among them, Δ represents the small - signal quantity of the variable; the superscript "s" represents the variable in the actual coordinate system; the superscript "c" represents the variable in the control coordinate system; X represents the stator voltage and rotor voltage and current of the doubly - fed wind turbine; θ and E are the power synchronization generation angle and the voltage loop amplitude given value respectively; G3 is the transformation matrix between the system rotation coordinate system and the control rotation coordinate system; P e and Q e are the stator active power and reactive power respectively; U sdq , I sdq are the d - axis and q - axis components of the stator voltage and current of the doubly - fed wind turbine respectively; I sd0 , I sq0 are the steady - state values of the d - axis and q - axis of the stator current respectively; U sd0 , U sq0are the steady-state values ​​of the stator voltage d-axis and q-axis respectively; G4 and G5 are the stator voltage-power change matrix and the stator current-power change matrix; Q ref represents the reactive power command given value; J and D represent the active inertia and active damping coefficient of the network control respectively; s is the Laplace operator; ω1 is the power frequency angular frequency; H Q is the reactive power controller; T e is the electromagnetic torque of the motor.

[0060] S14: The above three small signal models are combined and a mathematical model of the electromagnetic torque-speed difference of the grid-type doubly fed wind turbine is obtained through elimination.

[0061] Specifically, the above three small signal models are combined, and the mathematical model of electromagnetic torque-speed difference of grid-type doubly fed wind turbine is obtained through elimination. According to the mathematical model, the small signal model block diagram and the Bode diagram of electromagnetic torque-speed difference are drawn, the shaft system natural oscillation frequency of the doubly fed wind turbine is intercepted, and the shaft system damping is analyzed in combination with the Bode diagram.

[0062] The mathematical model is as follows:

[0063]

[0064] Where, ΔT e and Δω Δ are the small signal components of electromagnetic torque and speed difference, ω1 is the power frequency angular frequency; k is the ratio of equivalent motor inertia to equivalent wind wheel inertia; G7 is the speed-power command change matrix; G 0_1 and G 0_2 They are the stator current-stator voltage change matrix and the rotor current-stator voltage change matrix respectively; G 0_3 , G 0_4 and G 0_5 They are stator current-rotor voltage change matrix, rotor current-rotor voltage change matrix and speed-rotor voltage change matrix respectively; G1 is the main circuit change matrix; G 2_0 and G 2_1 are the coefficient change matrices caused by control, G 2_3 and G 2_4 For the voltage loop and current loop controller; G 3_1 , G 3_2 , G 3_3 They are the transformation matrices between the stator voltage, rotor current, and rotor voltage coordinate systems respectively; G4 and G5 are the stator voltage-power change matrix and the stator current-power change matrix.

[0065] S2: drawing a Bode diagram of electromagnetic torque and speed difference according to the mathematical model;

[0066] Specifically, Figure 3It is the phase-frequency characteristic diagram in the Bode diagram of the electromagnetic torque and speed difference corresponding to different operating regions. When the wind speed changes, the speed-power command change matrix G7 shows negative gain and positive gain in the maximum power tracking region and the constant speed region, resulting in significantly different phase characteristics of the grid-forming doubly-fed wind turbine at the natural oscillation frequency of the shafting in different operating regions, as Figure 3 shown, thus triggering the torsional vibration of the shafting of the doubly-fed wind turbine. Since the amplitude-frequency characteristic reflects the shafting damping magnitude and the phase-frequency characteristic reflects whether shafting torsional vibration will occur, for simplicity of analysis, this example only focuses on the phase-frequency characteristic of the Bode diagram and ignores the amplitude-frequency characteristic.

[0067] S3: Calculate the natural oscillation frequency of the shafting of the doubly-fed wind turbine according to the mechanical parameters of the wind turbine and the motor, and perform a stability analysis on the damping of the natural oscillation frequency of the shafting in combination with the Bode diagram;

[0068] Specifically, calculate the natural oscillation frequency of the shafting through the following formula:

[0069]

[0070] where, f osc is the natural oscillation frequency of the shafting; π is the pi; K m is the mechanical stiffness coefficient; H t , H g are the equivalent wind turbine inertia and the equivalent motor inertia respectively; ω1 is the power frequency angular frequency.

[0071] When the natural oscillation frequency of the shafting is obtained, analyze its corresponding phase on the Bode diagram, and the damping change at the natural oscillation frequency of the shafting in different operating regions can be analyzed. When its phase is in (90°, 270°), it indicates that the shafting damping is positive; when its phase is in (-90°, 90°), it indicates that the shafting damping is negative.

[0072] S4: Draw a small-signal model block diagram according to the mathematical model;

[0073] Specifically, Figure 4 is the small-signal model block diagram of the electromagnetic torque and speed difference of the grid-forming doubly-fed wind turbine. It can be seen from Figure 4 that the current loop provides a coupling path for speed and active power, thus changing the magnitude of the shafting damping. Compared with using the mathematical model, through the small-signal model block diagram, the influence of the current loop on the shafting damping can be intuitively reflected.

[0074] S5: Analyze the small-signal model block diagram to obtain the analysis result that the current loop provides a coupling path for speed and active power;

[0075] Specifically, to further analyze the role of the current loop, Figure 4 the small-signal transfer relationship shown can be transformed into Figure 5The form shown. Among them, branch 1 focuses on the influence of the current inner loop on the shaft damping, and branch 2 considers the operating region and the effect of the synchronization outer loop on the shaft damping. Figure 6 is the amplitude-frequency characteristic diagram of branch 1 under different current loop bandwidths. As the current loop bandwidth f c increases, the gain of branch 1 gradually decreases and can even be ignored, thus eliminating the influence of the current loop on the shaft damping. Therefore, as the current loop bandwidth increases, Figure 4 can be simplified to Figure 5 the branch 2 in Figure 5 . Since changing the operating region will cause the G7 link in branch 2 to exhibit opposite phase characteristics, as can be seen from the branch 2 in

[0076] S6: According to the stability analysis results and the analysis results of the small-signal model block diagram, by reducing the current loop bandwidth, the negative damping brought by the operating region is weakened, thereby reducing the risk of shaft torsional vibration.

[0077] Specifically, Figure 7 is the phase angle difference diagram under different current loop bandwidths and different operating regions. As the current loop bandwidth decreases, the phase difference θ diff between the electromagnetic torque and the speed difference gradually decreases, weakening the influence of the G7 link, making the shaft damping in both operating regions positive, and improving the stability of the grid-connected doubly-fed wind turbine during the operating region switching. For MW-level wind turbines, the control bandwidth of the current loop generally shall not be less than 100 Hz. Therefore, in this example, the current loop parameters when the phase angle difference θ diff = 90° are selected. When the wind speed changes and causes the operating region to switch, there is a risk of shaft torsional vibration. In order to weaken the negative damping caused by the change in the operating region gain, on the basis of ensuring the control performance of the wind turbine, the current loop bandwidth can be reduced to effectively avoid the shaft torsional vibration caused by the operating region switching.

[0078] Corresponding to the foregoing embodiments of the method for suppressing shaft torsional vibration of a grid-connected doubly-fed wind turbine under variable wind speed, the present application also provides an embodiment of a method for suppressing shaft torsional vibration of a grid-connected doubly-fed wind turbine under variable wind speed.

[0079] Figure 8 is a block diagram of a device for suppressing shaft torsional vibration of a grid-connected doubly-fed wind turbine under variable wind speed shown according to an exemplary embodiment. The device may include:

[0080] A construction module 1 for constructing a mathematical model of the electromagnetic torque - speed difference of the grid-connected doubly-fed wind turbine;

[0081] The first drawing module 2 is configured to draw a Bode diagram of electromagnetic torque - speed difference according to the mathematical model;

[0082] The calculation and analysis module 3 is configured to calculate the natural oscillation frequency of the shafting of the doubly-fed wind turbine according to the mechanical parameters of the wind turbine and the motor, and perform stability analysis on the damping of the natural oscillation frequency of the shafting in combination with the Bode diagram;

[0083] The second drawing module 4 is configured to draw a small-signal model block diagram according to the mathematical model;

[0084] The analysis module 5 is configured to analyze the small-signal model block diagram to obtain an analysis result that the current loop provides a coupling path for speed and active power;

[0085] The suppression module 6 is configured to reduce the negative damping brought by the operating region by reducing the current loop bandwidth according to the stability analysis result and the analysis result of the small-signal model block diagram, thereby reducing the risk of shafting torsional vibration.

[0086] Regarding the device in the above embodiments, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated herein.

[0087] For the device embodiments, since they basically correspond to the method embodiments, reference can be made to the partial descriptions of the method embodiments for the relevant parts. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present application. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0088] Correspondingly, the present application further provides an electronic device, including: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the method for suppressing shafting torsional vibration of a network-forming doubly-fed wind turbine under variable wind speed as described above. As Figure 9 shown, it is a hardware structure diagram of any device with data processing capabilities where the device for suppressing shafting torsional vibration of a network-forming doubly-fed wind turbine under variable wind speed provided by an embodiment of the present invention is located. In addition to Figure 9 the processors and memory shown, any device with data processing capabilities where the device in the embodiment is located usually further includes other hardware according to the actual functions of the device with data processing capabilities, which will not be elaborated herein.

[0089] Correspondingly, the present application further provides a computer-readable storage medium, on which computer instructions are stored, and when the instructions are executed by a processor, the method for suppressing shafting torsional vibration of a grid-forming doubly-fed wind turbine under variable wind speeds as described above is implemented. The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the foregoing embodiments, such as a hard disk or a memory. The computer-readable storage medium may also be an external storage device, such as a plug-in hard disk, a Smart Media Card (SMC), an SD card, a Flash Card, etc. equipped on the device. Further, the computer-readable storage medium may also include both an internal storage unit of any device with data processing capabilities and an external storage device. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store the data that has been output or is to be output.

[0090] Those skilled in the art will readily conceive of other embodiments of the present application after considering the specification and practicing the content disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

[0091] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A method for suppressing torsional vibration of the shafting of a grid-forming doubly-fed fan under variable wind speeds, characterized in that, include: Construct a mathematical model of electromagnetic torque-speed difference of grid-type doubly-fed wind turbine; According to the mathematical model, a Bode diagram of electromagnetic torque and speed difference is drawn; According to the mechanical parameters of the wind turbine and the motor, the shaft system natural oscillation frequency of the doubly-fed wind turbine is calculated, and the stability analysis of the damping of the shaft system natural oscillation frequency is performed in combination with the Bode diagram; According to the mathematical model, draw a small signal model block diagram; By analyzing the small signal model block diagram, the analysis result that the current loop provides a coupling path for the speed and active power is obtained; According to the stability analysis results and the analysis results of the small signal model block diagram, the risk of shaft torsional vibration is reduced by reducing the current loop bandwidth to weaken the negative damping brought by the operating area.

2. The method according to claim 1, wherein The mathematical model of electromagnetic torque-speed difference of grid-type doubly-fed wind turbine is constructed, including: According to the characteristics of the front-stage wind turbine of the doubly-fed wind turbine, the first small signal transmission model considering the mechanical transmission system link and the speed control link is established; According to the electrical control characteristics of the doubly-fed wind turbine, a second small signal transmission model is established that takes into account the doubly-fed wind turbine model, the voltage outer loop control link, and the current inner loop control link; According to the topology of the grid-type doubly-fed wind turbine generator system, the third smallest signal transmission model of the coordinate transformation link, power calculation link, power control link, and power torque link is established; The above three small signal models are combined and the mathematical model of electromagnetic torque-speed difference of grid-type doubly fed wind turbine is obtained through elimination.

3. The method according to claim 2, wherein The first small signal transfer model is as follows: Mechanical transmission system link: ; Speed control section: ; where, Δ represents the small-signal quantity of a variable; H t and H g are the equivalent wind turbine inertia and the equivalent motor inertia respectively; T m and T 12 and T e are the mechanical input torque of the wind turbine, the torque of the drive shaft, and the electromagnetic input torque of the motor respectively; ω t and ω r are the wind turbine speed and the generator speed respectively; θ Δ and ω Δ are the angular displacement and the speed difference of the wind turbine relative to the rotor of the doubly-fed wind turbine respectively; K m and D m are the mechanical stiffness coefficient and the mechanical damping coefficient; P ref represents the given value of the active power command, and G7 is the speed-power command change matrix; k opt represents a constant related to the wind turbine, and ω t0 is the wind turbine speed during the steady-state operation of the wind turbine; H ω represents the speed controller.

4. The method according to claim 2, characterized in that, The second small signal transfer model is as follows: Doubly-fed wind turbine model: ; Voltage outer loop control link: ; Inner current loop control section: ; where, Δ represents the small-signal quantity of a variable; U sdq 、I sdq 、U rdq 、I rdq are the dq-axis components of the stator voltage and current, and the rotor voltage and current of the doubly-fed wind turbine, respectively; s is the Laplace operator; ω1 is the power frequency angular frequency; R s 、R r 、L s 、L r 、L m are the stator and rotor resistances, stator and rotor inductances, and mutual inductance, respectively; ω s is the slip angular frequency; ψ rd0 、ψ rd0 are the steady-state values of the d-axis and q-axis of the rotor flux linkage, respectively; G 0_1 and G 0_2 are the stator current-stator voltage change matrix and rotor current-stator voltage change matrix, respectively; G 0_3 、G 0_4 and G 0_5 are the stator current-rotor voltage change matrix, rotor current-rotor voltage change matrix, and speed-rotor voltage change matrix, respectively; G 2_0 and G 2_1 are the coefficient change matrices caused by control, respectively; G 2_3 and G 2_4 are the voltage loop and current loop controllers; the superscript "ref” represents the command value of the corresponding variable; θ and E are the power synchronization generation angle and the voltage loop amplitude given value, respectively; the superscript "s” represents the variable in the actual coordinate system; the superscript "c” represents the variable in the control coordinate system.

5. The method according to claim 2, characterized in that The third small signal transmission model is as follows: Coordinate transformation section: ; Power calculation section: ; Power control section: ; Power torque model: ; where, Δ represents the small-signal quantity of a variable; the superscript "s" represents the variable in the actual coordinate system; the superscript "c" represents the variable in the control coordinate system; X represents the stator voltage and rotor voltage and current of the doubly-fed wind turbine; θ and E are the power synchronization generation angle and the given value of the voltage loop amplitude respectively; G3 is the transformation matrix between the system rotating coordinate system and the control rotating coordinate system; P e and Q e are the stator active power and reactive power respectively; U sdq 、I sdq 、are the dq-axis components of the stator voltage and current of the doubly-fed wind turbine respectively; I sd0 、I sq0 are the steady-state values of the d-axis and q-axis of the stator current respectively; U sd0 、U sq0 are the steady-state values of the d-axis and q-axis of the stator voltage respectively; G4 and G5 are the stator voltage-power change matrix and the stator current-power change matrix respectively; Q ref represents the given value of the reactive power command; J and D represent the active inertia and active damping coefficient of the grid-forming control respectively; s is the Laplace operator; ω1 is the power frequency angular frequency; H Q is the reactive power controller; T e is the electromagnetic torque of the motor.

6. The method according to claim 1 or 2, characterized in that, The mathematical model of electromagnetic torque-speed difference of the grid-type doubly-fed wind turbine is as follows: ; where, ΔT e and Δω Δ are the small-signal components of the electromagnetic torque and the speed difference respectively, ω1 is the power-frequency angular frequency; k is the ratio of the equivalent motor inertia to the equivalent wind turbine inertia; G7 is the speed-power command change matrix; G 0_1 and G 0_2 are the stator current-stator voltage change matrix and the rotor current-stator voltage change matrix respectively; G 0_3 、G 0_4 and G 0_5 are the stator current-rotor voltage change matrix, the rotor current-rotor voltage change matrix and the speed-rotor voltage change matrix respectively; G1 is the main circuit change matrix; G 2_0 and G 2_1 are the coefficient change matrices caused by control respectively, G 2_3 and G 2_4 are the voltage loop and current loop controllers; G 3_1 、G 3_2 、G 3_3 are the transformation matrices between the stator voltage, rotor current, and rotor voltage coordinate systems respectively; G4 and G5 are the stator voltage-power change matrix and the stator current-power change matrix.

7. The method according to claim 1, characterized in that, The shaft natural oscillation frequency of the doubly fed wind turbine is calculated by the following formula: ； where f osc is the natural oscillation frequency of the shafting; π is the pi; K m is the mechanical stiffness coefficient; H t , H g are the equivalent wind turbine inertia and the equivalent motor inertia respectively; ω1 is the power frequency angular frequency. Then, the damping of the natural oscillation frequency of the shafting is analyzed in combination with the said Bode plot.

8. The method according to claim 1, wherein According to the mathematical model, a small signal model block diagram including a transmission system, a speed loop, a synchronous outer loop, and a current inner loop is drawn.

9. A device for suppressing torsional vibration of the shafting of a grid-forming doubly-fed wind turbine under variable wind speeds, characterized in that, include: A construction module is used to construct a mathematical model of electromagnetic torque-speed difference of a grid-type doubly-fed wind turbine; A first drawing module is used to draw a Bode diagram of electromagnetic torque-rotation speed difference according to the mathematical model; A calculation and analysis module, used to calculate the shaft system natural oscillation frequency of the doubly-fed wind turbine according to the mechanical parameters of the wind turbine and the motor, and to perform stability analysis on the damping of the shaft system natural oscillation frequency in combination with the Bode diagram; A second drawing module, used for drawing a small signal model block diagram according to the mathematical model; An analysis module, used for analyzing the small signal model block diagram to obtain an analysis result that the current loop provides a coupling path for the speed and the active power; The suppression module is used to reduce the risk of shaft torsional vibration by reducing the negative damping caused by the operating area by reducing the current loop bandwidth according to the stability analysis results and the analysis results of the small signal model block diagram.

10. An electronic device, characterized in that, include: one or more processors; A memory for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 8.

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