Method, device, equipment and storage medium for predicting torsional vibration of net-forming type direct-driven fan

Abstract

The invention belongs to the technical field of fan torsional vibration prediction, and particularly relates to a torsional vibration prediction method, device and equipment for a net-forming type direct-driven fan and a storage medium, and the method comprises the steps: constructing a small signal model of the net-forming type direct-driven fan; based on a shafting dual-mass-block model, deducing the relation between the direct-drive fan port voltage and current signals and the direct-drive fan shafting torsional vibration when forced oscillation occurs; when forced oscillation occurs, a transfer function between different power grid node ports is obtained by constructing a wind power plant s domain node admittance model, so that required voltage and current signals of the power grid node ports are calculated, and the calculated voltage and current signals are used as input of a small signal model of a grid-constructing type direct-driven fan. And calculating the torsional vibration of the shaft system of the mesh-forming type direct-drive fan caused by forced oscillation by combining the relationship between the voltage and current signals of the port of the mesh-forming type direct-drive fan and the torsional vibration of the shaft system of the mesh-forming type direct-drive fan. The potential torsional vibration problem can be found and processed in time, and faults are avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of fan torsional vibration prediction, and specifically relates to a method, device, equipment and storage medium for predicting torsional vibration of a grid-type direct-drive fan. Background Art

[0002] There are always small disturbances in the power system. More and more low-frequency oscillations are proven to be not caused by insufficient damping, but forced oscillations caused by continuous and periodic small disturbances in the system. Generally speaking, when there are periodic disturbances that cannot be ignored in the grid-connected system, the system becomes a typical non-autonomous system. In the state equation of the system, the solution of the state variable contains two parts: the free oscillation part of the system and the pure forced oscillation part caused by external disturbances.

[0003] When the frequency of the external periodic disturbance is close to the natural frequency of the system, external resonance may occur even if the system damping is positive. External resonance can cause large power oscillations and frequency and voltage fluctuations of the system. Previous research on new energy grid connection has mainly focused on the problem of negative damping free oscillation of grid-following equipment in weak grid scenarios. Some literature points out that grid-building equipment still has a high stability margin in weak grid scenarios. However, these studies did not discuss the impact of forced oscillations on the safe operation of grid-building equipment in weak grid scenarios. When external resonance caused by forced oscillation occurs, the frequency and voltage fluctuations of the grid may cause the grid-building equipment to become unstable or even disconnect from the grid. When the grid-building equipment contains mechanical shafts, external resonance may cause shaft torsional vibration, which seriously threatens the safe operation of the equipment.

[0004] In summary, small disturbances in the power system may cause forced oscillations, which may cause external resonance under certain conditions (such as when the frequency of the external disturbance is close to the natural frequency of the system), posing a serious threat to the frequency, voltage and safe operation of the power grid equipment. Summary of the invention

[0005] In view of the problem that when a meshing device contains a mechanical shaft, external resonance may cause shaft system torsional vibration, seriously threatening the safe operation of the equipment, the present invention provides a torsional vibration prediction method, device, equipment and storage medium for a meshing type direct-drive wind turbine.

[0006] In a first aspect, the technical solution of the present invention provides a method for predicting torsional vibration of a grid-type direct-drive wind turbine, comprising the following steps: Construct a small signal model of a grid-type direct-drive wind turbine; Based on the shaft double mass model, the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine when forced oscillation occurs is derived. The double mass includes the generator mass and the turbine mass. When forced oscillation occurs, the transfer function between different grid node ports is obtained by constructing the s-domain node admittance model of the wind farm, so as to calculate the required grid node port voltage and current signals, that is, the port voltage and current signals of the grid-type direct-drive wind turbine. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine caused by forced oscillation is calculated based on the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine.

[0007] As a preferred embodiment of the technical solution of the present invention, the steps of constructing a small signal model of a grid-type direct-drive fan include: Construct a small signal model of the grid-side converter of a grid-connected direct-drive wind turbine; Construct a small signal model of the direct-drive wind turbine side of the grid; The grid-side converter small signal model of the grid-type direct-drive wind turbine and the small signal model of the grid-type direct-drive wind turbine are combined in series to form a complete small signal model of the grid-type direct-drive wind turbine.

[0008] As a preferred embodiment of the technical solution of the present invention, the steps of constructing a small signal model of a grid-side converter of a grid-type direct-drive wind turbine include: Constructing the state equation of the power loop, specifically including: constructing the state equation of the first-order low-pass link and performing linear processing; constructing the state equation of the active power link and performing linear processing; constructing the state equation of the reactive power link and performing linear processing; Construct the voltage and current double closed loop state equation and perform linearization processing; Construct the state equation of the filter circuit and perform linearization; Integrate and construct the power loop, voltage and current double closed loops, and state equations of the filter circuit; The integrated state equation is converted into a small signal equation to obtain the small signal model of the grid-side converter of the grid-connected direct-drive wind turbine.

[0009] As a preferred embodiment of the technical solution of the present invention, the machine-side structure of a grid-type direct-drive wind turbine includes a machine-side converter, a synchronous generator and a wind turbine, wherein the machine-side converter is connected to the grid-side converter and the synchronous generator, the synchronous generator rotor is connected to the wind turbine through a mechanical shaft, the wind turbine rotates under the drive of wind, and the synchronous generator rotor is driven to rotate and generate electricity through the mechanical shaft; the steps of constructing a small signal model of the machine-side of a grid-type direct-drive wind turbine include: Constructing a small signal model of the machine-side converter, specifically including: constructing a small signal model of the current command value function of the machine-side converter; constructing a small signal model of the current inner loop control of the machine-side converter with the current command value of the machine-side converter as input; Construct a small signal model of the rotor shaft system between the synchronous generator and the wind turbine considering low-frequency dynamics, specifically including: constructing a small signal model of the mechanical torque inner loop of the wind turbine; constructing a small signal model of the electromagnetic torque inner loop of the synchronous generator; constructing a shaft system double-mass block model and describing the transmission relationship between the wind turbine and the synchronous generator; A small signal model generated by the electromagnetic torque command value of the synchronous generator and the pitch angle command value of the wind turbine is constructed, which describes the small signal model of the control outer loop of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

[0010] As a preferred embodiment of the technical solution of the present invention, based on the shaft system double mass block model, the step of deriving the relationship between the port voltage and current signals of the meshed direct-drive fan and the torsional vibration of the shaft system of the meshed direct-drive fan when forced oscillation occurs includes: The state matrix generated by normalizing the shaft system state space equation based on the shaft system dual-mass block model is converted into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode, and the mapping relationship between the actual torque angle mode and the decoupled torque angle mode is obtained, that is, the relationship between the port voltage and current signals of the grid-type direct-drive fan and the torsional vibration of the shaft system of the grid-type direct-drive fan is obtained.

[0011] As a preferred embodiment of the technical solution of the present invention, the step of converting the state matrix generated by normalizing the state space equation of the shaft system based on the shaft system dual mass block model into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode includes: Normalize the state space equation of the shaft system based on the shaft system double mass model to generate a state matrix; Diagonalize the normalized state matrix, extract the left and right eigenvectors, and obtain the decoupled matrix; The gain, damping coefficient and oscillation frequency of each mode are calculated based on the decoupled matrix.

[0012] As a preferred embodiment of the technical solution of the present invention, when forced oscillation occurs, by constructing a wind farm s-domain node admittance model, a transfer function between different grid node ports is obtained, thereby calculating the required grid node port voltage and current signals, that is, the grid-type direct-drive wind turbine port voltage and current signals, and using the calculated voltage and current signals as inputs of a small signal model of the grid-type direct-drive wind turbine. The steps of calculating the grid-type direct-drive wind turbine shaft system torsional vibration caused by forced oscillation in combination with the relationship between the grid-type direct-drive wind turbine port voltage and current signals and the grid-type direct-drive wind turbine shaft system torsional vibration include: When forced oscillation occurs, the voltage and current signals of the power grid node ports equipped with PMU measurement equipment are measured; The transfer function between different grid node ports is obtained by constructing the wind farm s-domain node admittance matrix, and the voltage and current signals of the grid-type direct-drive wind turbine ports are calculated based on the measured voltage and current signals. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine to calculate the electromagnetic power small signal of the grid-type direct-drive wind turbine ports. Constructing a transfer function relationship between the electromagnetic power small signal of the meshed direct-drive wind turbine port, the electromagnetic torque small signal of the synchronous generator, and the mechanical speed small signal of the synchronous generator rotor, and calculating the electromagnetic torque of the synchronous generator in combination with the electromagnetic power of the meshed direct-drive wind turbine port; constructing a transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine, and calculating the mechanical torque of the wind turbine in combination with the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine; The magnitude of the torsional vibration of the grid-type direct-drive wind turbine shaft system is calculated based on the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine, combined with the mapping relationship between the actual torque angle mode and the decoupled torque angle mode.

[0013] In a second aspect, the technical solution of the present invention further provides a torsional vibration prediction device for a grid-type direct-drive wind turbine, comprising a model building module, a torsional vibration modal analysis module and a shaft system torsional vibration estimation module; Model building module, used to build a small signal model of a grid-type direct-drive wind turbine; The torsional vibration modal analysis module is used to derive the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the grid-type direct-drive wind turbine shaft system when forced oscillation occurs based on the dual-mass model of the shaft system, wherein the dual-mass model includes a generator mass block and a turbine mass block; The shaft torsional vibration estimation module is used to obtain the transfer function between different grid node ports by constructing the wind farm s-domain node admittance model when forced oscillation occurs, so as to calculate the required grid node port voltage and current signals, that is, the port voltage and current signals of the grid-type direct-drive wind turbine. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the shaft torsional vibration of the grid-type direct-drive wind turbine caused by forced oscillation is calculated by combining the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the shaft torsional vibration of the grid-type direct-drive wind turbine.

[0014] As a preferred embodiment of the technical solution of the present invention, the model building module includes a network side model building unit, a machine side model building unit and a connection unit; A grid-side model building unit, used to build a small signal model of the grid-side converter of a grid-type direct-drive wind turbine; The machine-side model building unit is used to build a small signal model of the machine-side of a grid-type direct-drive wind turbine; The connection unit is used to connect the grid-side converter small signal model of the grid-type direct-drive wind turbine with the grid-type direct-drive wind turbine side small signal model in series to form a complete small signal model of the grid-type direct-drive wind turbine.

[0015] As a preferred embodiment of the technical solution of the present invention, the grid-side model construction unit is specifically used to construct the state equation of the power loop, which specifically includes: constructing the state equation of the first-order low-pass link and linearizing it; constructing the state equation of the active power link and linearizing it; constructing the state equation of the reactive power link and linearizing it; constructing the state equation of the voltage and current double closed loop and linearizing it; constructing the state equation of the filter circuit and linearizing it; integrating the constructed power loop, the voltage and current double closed loop and the state equation of the filter circuit; converting the integrated state equation into a small signal equation to obtain a small signal model of the grid-side converter of the grid-type direct-drive wind turbine.

[0016] As a preferred embodiment of the technical solution of the present invention, the machine-side structure of the grid-type direct-drive wind turbine includes a machine-side converter, a synchronous generator and a wind turbine, wherein the machine-side converter is connected to the grid-side converter and the synchronous generator, the synchronous generator rotor is connected to the wind turbine through a mechanical shaft, the wind turbine rotates under the drive of wind, and the synchronous generator rotor is driven to rotate and generate electricity through the mechanical shaft; The machine-side model building unit is specifically used to build a small signal model of the machine-side converter, which specifically includes: building a small signal model of the machine-side converter current command value function; building a small signal model of the machine-side converter current inner loop control with the machine-side converter current command value as input; building a small signal model of the rotor shaft system between the synchronous generator and the wind turbine considering low-frequency dynamics, which specifically includes: building a small signal model of the mechanical torque inner loop of the wind turbine; building a small signal model of the electromagnetic torque inner loop of the synchronous generator; building a shaft system double-mass block model and describing the transmission relationship between the wind turbine and the synchronous generator; building a small signal model generated by the electromagnetic torque command value of the synchronous generator and the pitch angle command value of the wind turbine, which describes the small signal model of the control outer loop of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

[0017] As a preferred embodiment of the technical solution of the present invention, the torsional vibration modal analysis module includes a calculation processing unit and a mapping relationship acquisition unit; A calculation processing unit is used to convert the state matrix generated by normalizing the state space equation of the shaft system based on the dual-mass block model of the shaft system into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode; specifically, it is used to normalize the state space equation of the shaft system based on the dual-mass block model of the shaft system to generate a state matrix; diagonalize the normalized state matrix to extract the left and right eigenvectors to obtain a decoupled matrix; and calculate the gain, damping coefficient and oscillation frequency of each mode based on the decoupled matrix; The mapping relationship acquisition unit is used to obtain the mapping relationship between the actual torque angle mode and the decoupled torque angle mode, that is, to obtain the relationship between the port voltage and current signals of the network-type direct-drive fan and the torsional vibration of the direct-drive fan shaft system.

[0018] As a preferred embodiment of the technical solution of the present invention, the shaft system torsional vibration estimation module is specifically used to measure the voltage and current signals of the grid node port equipped with the PMU measurement device when forced oscillation occurs; obtain the transfer function between different grid node ports by constructing the wind farm s-domain node admittance matrix, and calculate the voltage and current signals of the meshed direct-drive wind turbine port based on the measured voltage and current signals, and use the calculated voltage and current signals as the input of the small signal model of the meshed direct-drive wind turbine to calculate the electromagnetic power small signal of the meshed direct-drive wind turbine port; construct the electromagnetic power small signal of the meshed direct-drive wind turbine port and the synchronization The electromagnetic torque of the synchronous generator is calculated based on the transfer function relationship between the small signal of the electromagnetic torque of the generator and the small signal of the mechanical speed of the synchronous generator rotor, combined with the electromagnetic power of the port of the meshed direct-drive wind turbine; the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine is constructed, and the mechanical torque of the wind turbine is calculated based on the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine; the magnitude of the torsional vibration of the shaft system of the meshed direct-drive wind turbine is calculated based on the mapping relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine combined with the actual torque angle mode and the decoupled torque angle mode.

[0019] In a third aspect, the technical solution of the present invention also provides an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; the memory stores computer program instructions executable by the at least one processor, and the computer program instructions are executed by the at least one processor so that the at least one processor can execute the torsional vibration prediction method of the grid-type direct-drive wind turbine as described in the first aspect.

[0020] In a fourth aspect, the technical solution of the present invention further provides a non-transitory computer-readable storage medium, wherein the non-transitory computer-readable storage medium stores computer instructions, and the computer instructions enable the computer to execute the torsional vibration prediction method of the grid-type direct-drive wind turbine as described in the first aspect.

[0021] It can be seen from the above technical solutions that the present invention has the following advantages: by constructing a small signal model of a meshed direct-drive fan, the method can accurately reflect the small signal transmission relationship between the fan shaft system and the port voltage and current, thereby greatly improving the accuracy of the prediction of the torsional vibration of the direct-drive fan shaft system.

[0022] Combined with the established small signal model, this method can monitor the forced oscillation phenomenon in the wind farm system in real time. By constructing the s-domain node admittance model of the wind farm system, the transfer function between different ports can be easily obtained. Then, when forced oscillation occurs, the torsional vibration of the wind turbine shaft system can be quickly calculated by measuring the voltage and current signals of the port, thus avoiding the occurrence of faults.

[0023] This method can not only predict the torsional vibration of the shaft system of a direct-drive wind turbine, but also provide strong support for the operation and maintenance of wind farms. Through real-time monitoring and early warning, wind farm operators can timely understand the operating status of wind turbines and adjust the operating strategy according to actual conditions to optimize the overall performance of wind farms. At the same time, it also provides a scientific basis for regular maintenance and overhaul of wind turbines, reducing maintenance costs and extending the service life of equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 is a schematic flow chart of a method according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of a grid-type direct-drive wind turbine.

[0027] Figure 3 This is the VSG power loop control block diagram.

[0028] Figure 4 It is a working state diagram under different wind speeds, and a schematic diagram of torque control and pitch angle control.

[0029] Figure 5 It is the estimated value of the torsional vibration of the shaft system caused by disturbance when the wind speed is 11.5m / s, 11.7 / s and 12m / s respectively.

[0030] Figure 6 It is the voltage, current, electromagnetic torque disturbance and torsional vibration disturbance diagram of the system after the load impact is applied at 5s.

[0031] Figure 7 This is a comparison chart between the system torsional vibration waveform and the theoretical estimated waveform after the load impact is applied at 5s.

[0032] Figure 8 is a schematic block diagram of an apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] like Figure 1 As shown, an embodiment of the present invention provides a method for predicting torsional vibration of a grid-type direct-drive wind turbine, comprising: Step 1: Construct a small signal model of a grid-type direct-drive wind turbine; The grid-type direct-drive wind turbine adopts virtual synchronous machine VSG control. The small signal modeling process considering mechanical dynamics is introduced below: Among them, the schematic diagram of the grid-type direct-drive wind turbine is as follows Figure 2 The main body of the grid-type direct-drive wind turbine includes a wind turbine, a synchronous motor PMSG, a machine-side converter MSC, a grid-side converter GSC and a filter circuit, and the resistor Rg and the inductor Lg constitute the filter.

[0035] The wind turbine body mainly adopts pitch angle control, and the pitch angle command value The actual pitch angle After the difference is made, through the transfer function Control the pitch angle dynamically and output .

[0036] The machine-side converter MSC adopts fixed DC bus control, in which the control adopts fixed DC bus voltage control, and the control input is the collected DC bus voltage With bus voltage command value The difference, After the PI stage, we get and and input to the inner current loop, where is controlled to 0. The machine-side converter voltage is obtained through the inner loop control of the current loop and , and then input into the machine-side converter MSC.

[0037] The active power link controlled by the grid-side converter GSC adopts virtual synchronous machine control, and the input is the active power command value Active Power The difference is caused by the inertia of the equipment , droop coefficient and the damping coefficient After the virtual synchronization link is formed, the output is the power loop phase angle The reactive power link adopts droop control, and the input is the d-axis voltage command value The measured d-axis The difference between the two, after passing through the PI link and the power loop phase angle The synthesized output reference voltage is used as the input of the voltage and current dual closed-loop control. The output of the voltage and current dual closed-loop control is transformed by dq / abc and input into the grid-side converter GSC through space vector pulse width modulation SVPWM.

[0038] Figure 3 The virtual synchronous machine and reactive power droop control in the power loop are shown, and the input is the grid connection point voltage. , Current , after power calculation, we get the active power and reactive power , respectively input filter Then the output is as follows: and , are input into the virtual synchronous machine link and the reactive power droop link respectively, where the virtual synchronous machine link is shown in formulas (3) and (4), and the reactive power droop link is shown in formulas (5) and (6).

[0039] Grid-side converter impedance 1.1 Power loop 1) First-order low-pass link The state equations of the first-order low-pass link are shown in formulas (1) and (2); (1) (2) In the formula and They respectively represent the active power and reactive power output by the converter to the grid-connected point. represents the Laplace operator. and They represent the grid-connected point output voltage and current in the dq coordinate system respectively. Indicates the system power frequency angular velocity, which defaults to 50Hz here, which is the rated frequency.

[0040] 2) Active power link The state equation of the active power link is shown in formula (3); (3) in the formula Indicates the active power command value, Indicates the virtual angular frequency of the networking device. represents the inertia of the device, represents the droop coefficient, Represents the virtual damping coefficient of VSG control.

[0041] After linearization, we get: (4) 3) Reactive power link The state equation of the reactive power link is shown in formulas (5) and (6); (5) (6) In the formula Indicates the output dq voltage command value of the grid-connected point, represents the reactive power droop coefficient, represents the reactive power command value, and Indicates the reactive power output by the grid-connected point.

[0042] After linearization, we get: , ; The above equations (3), (4), (7), (8) can be uniformly described by state space equations as follows: (9) in is the state matrix of the power loop, represents the voltage input matrix of the power loop, and Represents the current input matrix of the power loop. and Together they form the output matrix.

[0043] The specific expression of each matrix is:

[0044]

[0045] 1.2 Voltage and current double closed loop The voltage loop is expressed as: (10) in is the voltage loop input, It is the output reference voltage of the power loop.

[0046] (11) in It is the inductor current command value output by the voltage loop. and Respectively represent the PI parameters of the current loop, Represents the parallel capacitance to ground.

[0047] The current loop is expressed as: (12) in is the current loop output.

[0048] (13) in is the voltage command value output by the current loop, represents the inductor current, and Respectively represent the PI parameters of the current loop, Represents the filter inductance.

[0049] The linearization of formula (10) yields: (14) The linearization of formula (11) yields: (15) The linearization of formula (12) yields: (16) The linearization of formula (13) yields: (17) In the formula is the state matrix of the voltage loop, , represents the voltage input matrix of the voltage loop, represents the voltage loop output state matrix, and represents the voltage loop transfer function matrix. is the state matrix of the current loop, , represents the input matrix of the current loop, represents the current loop output state matrix, Represents the current loop transfer function matrix. The definitions of each part are as follows: .

[0050] 1.3 Filter circuit link The output voltage and current links of the grid-side converter can be described in the form of formula (18): (18) Where: Represents the dq-axis component of the inverter output bridge arm voltage, and They represent the series resistance of the converter and the filter inductance respectively; Represents the parallel capacitance to ground.

[0051] After linearization, the state space model of the filter and the grid output is obtained: (19) in is the state matrix of the filter and series resistance link, Represents the input matrix of the filter and series resistance link. Each matrix is ​​specifically expressed as:

[0052]

[0053] (20) 1.4 Integrating the state equation and input-output equations

[0054] Among them, the power ring , voltage and current double closed loop , filter and series impedance ; State variables , and are the input and output quantities.

[0055] (twenty one) The definitions of each part are as follows:

[0056]

[0057] The input is quantized to just The output quantization is simplified to only ; First, decompose the matrix in equation (21) to obtain: (twenty two) (twenty three) (twenty four) By eliminating variables, the formula is finally made to contain only state variables and input and output .

[0058] Note that the following approximations are made in the process of eliminating the input and output equations: , this is because the delay link is ignored.

[0059] After elimination, the input and output equations are as follows: (25) Will Moving to the other side we get: (26) (27) in .

[0060] 1.5 Transformation of state-space equations into impedance The state equation is written as follows: (28) Further split the B array into , the state equation is obtained: (29) After Laplace transform, , thus obtaining: (30) Substituting equation (30) into the input equation, we finally get the admittance: (31) There is an inverse relationship between admittance and impedance ; Finally, the grid-side converter impedance of the grid-type direct-drive wind turbine is obtained. , that is, the small signal model of the grid-side converter of the grid-type direct-drive wind turbine.

[0061] 2. Modeling of the direct-drive wind turbine side with grid-type considering mechanical dynamics 1.1 MSC impedance 1) Current command value function like Figure 2 As shown in the figure, the small signal model of the grid-type direct-drive wind turbine considering the current controller is as follows: (32) In the formula represents the d-axis current command value, Indicates the electromagnetic torque and flux relationship on the machine side Equation (32) shows that the d-axis current command value of the grid-type direct-drive wind turbine is related to the electromagnetic torque The current command value of the q axis is constant, which will make . So the transfer function relationship of the current inner loop command value is obtained as follows: (33) In the formula .

[0062] 2) Current inner loop control model like Figure 2As shown, the internal current control of MSC is similar to that of GSC, with one major difference being the angular frequency Decoupling terms involved Dynamic behavior of the inductor. It is called the transient inductance of the rotor.

[0063] The input quantity of the current inner loop includes the stator current control quantity and the command value from the voltage loop , and the rotor electrical angular velocity .

[0064] (34) In the formula and A small signal representing the rotor voltage and current control quantity, Represents the electrical angular velocity of the rotor, and the impedance variables are: (35) (36) (37) Electrical angular velocity of the rotor Directly with mechanical angular velocity So it will be further deduced later.

[0065] 1.2 Rotor modeling considering mechanical low-frequency dynamics The shaft system double-mass model and electromagnetic torque function will be used to describe the shaft system dynamic model of the grid-type direct-drive wind turbine.

[0066] 1) Mechanical torque model of wind turbine After considering the aerodynamic model of the fan, Figure 2 As shown, the small signal model of the mechanical torque of the wind turbine is as follows: (38) The small signal variables are defined as follows: the mechanical torque of the wind turbine , wind speed , small signal of pitch angle , small signal of mechanical angular velocity The coefficients are defined as follows: represents the air density, Represents the mechanical torque coefficient.

[0067] The dynamics of the pitch angle is determined by its command value: (39) In the formula represents the transfer function of pitch angle regulation, Indicates the command value of the pitch angle.

[0068] 2) Electromagnetic torque model of synchronous generator The small signal model of electromagnetic torque is expressed as follows: (40) The small signal of electromagnetic torque is expressed as .

[0069] (41) (42) In the formula A small signal quantity representing the electromagnetic torque, represents the small signal of the stator current, and A small signal representing the rotor current.

[0070] 3) Transmission process between wind turbine and synchronous generator The interaction between mechanical torque and electromagnetic torque jointly affects the dynamics of rotor speed. By modeling the dual mass model, we can obtain: (43) (44) (45) In the formula describes the moment of inertia of the wind turbine mass, and Describes the moment of inertia of the mass of the generator pulled by the wind turbine. , , and represents the damping coefficient and stiffness coefficient of each mass block in the dual-mass model, which can describe the flexible connection relationship of the dual-mass model. represents the damping coefficient of the wind turbine shaft system, represents the damping coefficient of the generator shaft system, and They respectively represent the gain coefficient and damping coefficient of the flexible transmission chain connecting the two mass blocks.

[0071] (46) In the formula is a state variable , The rotor angular velocity The transfer function between represents the moment of inertia; (47) In the formula, Depends on the drive shaft parameters, wind speed and turbine speed .

[0072] 2.3 Generation of electromagnetic torque command value and pitch angle command value The transmission relationship between the wind turbine and the synchronous generator was introduced in Section 2.2. Here we introduce the control process of the inputs on both sides of the transmission system - electromagnetic torque and mechanical torque. The selected grid-type direct-drive wind turbine adopts speed command control, and the electromagnetic torque command value of the wind turbine is The mechanical speed The pitch angle command value is also controlled by the mechanical speed. The mechanical speed reflects the current wind speed of the grid-type direct-drive wind turbine. and operating mode.

[0073] like Figure 4 As shown in the figure, the grid-type direct-drive wind turbine has different wind speeds. The operating status is different. Figure 4 (a) in the figure shows the four operating areas of the grid-type direct-drive wind turbine. When the grid-type direct-drive fan is in a constant speed state, When working in maximum power mode, at wind speed When the wind speed is constant, When the electromagnetic torque of the grid-type direct-drive fan is Generally, it will not increase any more, and the grid-type direct-drive wind turbine will gradually transition to the full load state. and mechanical speed are different. Figure 4 (b) shows the details of torque control, depending on whether the speed exceeds and The transfer function of the torque output of the switching grid-type direct-drive wind turbine When the grid-type direct-drive wind turbine is running in mode 1 to 3, torque control is activated. It should be emphasized that the torque control is based on the speed. Exceed the limit? Determine the torque output command value of the grid-type direct-drive fan Whether the output is 0, that is, whether the fan enters the constant speed state. Figure 4 (c) in the figure represents the pitch angle control of the grid-type direct-drive wind turbine, where Represents the transfer function of pitch angle control.

[0074] In order to control the grid-type direct-drive fan to meet the above operating rules, Figure 4 As shown in (b) and (c) in the figure, the electromagnetic torque command value of the grid-type direct-drive fan and pitch angle command value It is controlled by mechanical speed; (48) (49) In the formula Indicates the mechanical speed of the grid-type direct-drive fan The transfer function relationship between and electromagnetic torque command value is Indicates the mechanical speed of the grid-type direct-drive fan Pitch angle The transfer function relationship between them.

[0075] The pitch angle command value is described by equation (49): Control pitch angle The transfer function of the pitch angle is then With mechanical speed The transfer function between: (50) In the formula represents the control transfer function of the wind turbine pitch angle. The transfer function in equation (49) and equation (50) is and It is customized.

[0076] Substitute equation (50) into equation (46) and eliminate , the synchronous generator rotor angular velocity can be obtained With electromagnetic torque The transfer function between: (51) In the formula As shown below: (52) 2.4 Overall modeling of grid-type direct-drive wind turbine 1) Stator converter impedance From formula (31), we can see that the stator converter impedance of the grid control is for: (53) 2) Rotor converter impedance Rotor converter impedance It can be described as: (54) In the formula , Respectively represent the stator side and rotor side impedance in the motor; (55) (56) in and represents the resistance and inductance of the click stator, and Indicates the power frequency angular velocity; Represents the inductance of the motor rotor.

[0077] and The specific form is as follows: (57) (58) Step 2: Based on the shaft double mass model, derive the relationship between the port voltage and current signals of the grid-type direct-drive fan and the torsional vibration of the shaft system of the grid-type direct-drive fan when forced oscillation occurs; Since the state equation matrix of the shaft system with multiple mass blocks is not a diagonal matrix, it is not convenient to intuitively measure the torsional vibration degree of the shaft system of the direct-drive wind turbine. Therefore, for a shaft system with multiple mass blocks, the shaft system needs to be decoupled first, that is, the state matrix after the normalization of the shaft system state space equation is converted into a diagonal matrix, and then the gain, damping coefficient and oscillation frequency of each mode are extracted.

[0078] (59) The variable definitions that need to be pointed out in the formula include: represents the angular displacement of the wind turbine mass, and Represents the angular displacement of the generator mass.

[0079] The matrix of equation (59) is diagonalized (decoupled). The specific decoupling process is as follows: First, the moment of inertia matrix Diagonalize and extract left and right eigenvectors , and get the decoupled matrix ; (60) By vector Continue processing Zhenhe Array. Due to the existence of the transmission chain damping coefficient It is impossible to achieve diagonalization. Combined with the actual parameters, it is believed that the off-diagonal terms are small and can be approximated as diagonalization: (61) After the matrix is ​​diagonalized, only one item remains, because N The mass block model usually contains only N -1 gain factor.

[0080] (62) (63) The dual-mass matrix contains only two modes, and the gain, damping, and angular frequency of each mode are calculated as follows: (64) (65) (66) After the diagonalization of the dual-mass model, the electromagnetic torque mode and shaft torque angle mode It can be expressed by the classic second-order transfer function model of equation (67): (67) Actual torque angle mode and There is a mapping relationship between (wind turbine mass block and generator mass block) and the decoupled torque angle mode as follows: (68) Step 3: When forced oscillation occurs, the transfer function between different grid node ports is obtained by constructing the wind farm s-domain node admittance model, so as to calculate the required grid node port voltage and current signals, that is, the grid-type direct-drive wind turbine port voltage and current signals. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the torsional vibration of the grid-type direct-drive wind turbine shaft caused by forced oscillation is calculated by combining the relationship between the voltage and current signals of the grid-type direct-drive wind turbine port and the torsional vibration of the grid-type direct-drive wind turbine shaft.

[0081] The wind farm s-domain node admittance matrix can be described as follows: (69) In the formula Represents the voltage and current small signal matrix of each node, and the s-domain node impedance / admittance matrix It is composed of a 2×2 dq impedance / admittance matrix for each device.

[0082] When forced oscillation occurs in a system, it means that there is a persistent disturbance somewhere in the system. Even if the system is not completely unstable (the system damping is positive, or There is no positive zero point in the determinant zero point). Once forced oscillation occurs, oscillation will still be measured in various parts of the system, and the amplitude and phase of the oscillation will change after propagating through the system. This change is determined by the overall impedance characteristics of the system.

[0083] The control safety of grid-type wind turbines pays special attention to external power fluctuations, especially in strong power grids. When forced power oscillation occurs, it is easy to cause drastic changes in the power loop, which is different from the characteristics of traditional grid-following equipment. When there is a large power disturbance caused by forced oscillation outside, it causes rapid changes in the output of the grid control, and the rapid power output fluctuations caused by the grid side will be transmitted to the rotor side through the bus capacitor and cause shaft torsional vibration. When the torsional vibration is more severe, it will seriously threaten the safety of the equipment. Therefore, when there is forced power oscillation in the system, it is necessary to pay attention to the shaft torsional vibration safety of the grid-type direct-drive wind turbine.

[0084] When forced oscillation occurs, the fan shaft torsional vibration can be calculated by measuring the voltage and current small signals at the port. The specific process is as follows: Small electromagnetic power signal at the port of a known grid-type direct-drive wind turbine The synchronous generator electromagnetic torque small signal And the synchronous generator mechanical speed small signal The transfer function relationship between them is: (70) Substituting equation (51) into equation (70) yields: (71) Obviously, The voltage and current small signals can be obtained by measuring the power grid node port with PMU equipment installed: (72) Substituting formula (51) into formula (38), we can obtain: (73) in Describes the electromagnetic torque of the synchronous generator and wind turbine mechanical torque The transfer function relationship between them. As shown below: (74) In getting and After that, the torsional vibration can be calculated by equation (67): , and is reduced to natural torsional vibration through equation (68): and .

[0085] According to the shaft system torque calculation method proposed in formula (67), the magnitude of the shaft system torsional vibration can be estimated. Specifically, a system consisting of a thermal power plant, a wind farm and a load, wherein the thermal power plant contains a steam turbine driven, rated voltage 13.8KV, 200MVA excitation synchronous generator set, connected to the grid through a 13.8KV / 230KV step-up substation; the wind farm contains 25 identical direct-drive wind turbines with a rated voltage of 690V and a rated capacity of 2.5MW, which are connected in parallel through a collector line and then connected to the system through a 13.8KV / 230KV step-up substation. The thermal power plant and the wind farm are connected by a transmission line with a voltage level of 220KV.

[0086] First, the s-domain dq admittance matrix of the system is listed, as shown in formula (69), and the transfer function between different ports can be obtained. After retaining the dominant zeros and poles in the transfer function (this paper retains the two pairs of poles and one pair of zeros on the rightmost side of the figure), the voltage and current disturbance signals of the grid-connected direct-drive wind turbine when the accident occurs can be obtained; combined with the above method, the electromagnetic torque disturbance of the target wind turbine can be calculated , here the target wind turbine refers to the grid-type direct-drive wind turbine to be predicted.

[0087] Figure 5 It is the estimated value of the torsional vibration of the shaft system caused by the disturbance when the wind speed is 11.5m / s, 11.7 / s and 12m / s. After calculation, the torque of the system is different under different wind speed conditions after the disturbance at 5s. The high cycle fatigue limit of the shaft section of the grid-type direct-drive wind turbine is 1pu, and the warning value is selected as 0.8pu according to its 80% margin. At 12m / s, the system has become unstable, and the increased torque will destroy the shaft of the direct-drive wind turbine. There is no doubt that the system is unsafe at this time. At 11.5m / s, the system is still in a stable state, and the torque has not exceeded the fatigue limit for a long time, so it is considered safe. When the wind speed is 11.7m / s, although the system is still in a stable state through the pole, and the oscillation is in a decaying state, the shaft system has exceeded the warning value for more than 10s. At this time, the shaft is in a high fatigue loss state, which will trigger the shaft system protection.

[0088] By checking Increasing the load will cause the system to oscillate. The theoretical calculation results have not been verified. The SCR in the design model of this paper is 1.66 and the wind speed is 11.7m / s. The voltage and current at the grid connection point of the wind farm where the oscillation occurs, as well as the electromagnetic torque disturbance of the direct-drive wind turbine in the grid and torsional vibration like Figure 6 shown.

[0089] like Figure 7As shown in the figure, the red line represents the complex waveform of the torsional vibration of the simulation model under disturbance. The transient process in the first 5 seconds is slightly different from the theoretical estimated waveform. This is because the calculation error caused by ignoring non-dominant zeros and poles when calculating the aggregate impedance. After 5 seconds, the actual torsional vibration amplitude of the system is almost the same as the theoretical torsional vibration amplitude; the error between the simulated value and the estimated value of the oscillation frequency does not exceed 0.1Hz, which is within the normal error range. Figure 7 It shows that when the system impedance is known, the torsional vibration of the shaft system of the direct-drive wind turbine can be accurately calculated.

[0090] Through the above theoretical calculations and simulations, it is found that when the system SCR=1.66 and the wind speed of the wind farm is 11.7m / s, the system is in a stable state, but the shaft torsional vibration has triggered an early warning, and the traditional impedance method analysis ignores the shaft safety issue. This further shows that the direct drive impedance small signal model proposed in this paper that considers the shaft dynamics and operating points is of engineering guidance significance and can provide theoretical support for system stability analysis and direct drive unit shaft safety analysis.

[0091] like Figure 8 As shown, an embodiment of the present invention further provides a torsional vibration prediction device for a grid-type direct-drive wind turbine, comprising a model building module, a torsional vibration modal analysis module and a shaft system torsional vibration estimation module; Model building module, used to build a small signal model of a grid-type direct-drive wind turbine; The torsional vibration modal analysis module is used to derive the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the grid-type direct-drive wind turbine shaft system when forced oscillation occurs based on the dual-mass model of the shaft system, wherein the dual-mass model includes a generator mass block and a turbine mass block; The shaft torsional vibration estimation module is used to obtain the transfer function between different grid node ports by constructing the wind farm s-domain node admittance model when forced oscillation occurs, so as to calculate the required grid node port voltage and current signals, that is, the port voltage and current signals of the grid-type direct-drive wind turbine. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the shaft torsional vibration of the grid-type direct-drive wind turbine caused by forced oscillation is calculated by combining the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the shaft torsional vibration of the grid-type direct-drive wind turbine.

[0092] In the embodiment of the present invention, the model construction module includes a network side model construction unit, a machine side model construction unit and a connection unit; A grid-side model building unit, used to build a small signal model of the grid-side converter of a grid-type direct-drive wind turbine; The machine-side model building unit is used to build a small signal model of the machine-side of a grid-type direct-drive wind turbine; The connection unit is used to connect the grid-side converter small signal model of the grid-type direct-drive wind turbine with the grid-type direct-drive wind turbine side small signal model in series to form a complete small signal model of the grid-type direct-drive wind turbine.

[0093] Specifically, the grid-side model construction unit is specifically used to construct the state equation of the power loop, including: constructing the state equation of the first-order low-pass link and performing linear processing; constructing the state equation of the active power link and performing linear processing; constructing the state equation of the reactive power link and performing linear processing; constructing the state equation of the voltage and current double closed loop and performing linear processing; constructing the state equation of the filter circuit and performing linear processing; integrating the constructed power loop, the voltage and current double closed loop and the state equation of the filter circuit; converting the integrated state equation into a small signal equation to obtain the small signal model of the grid-side converter of the grid-type direct-drive wind turbine.

[0094] The machine-side structure of the grid-type direct-drive wind turbine includes a machine-side converter, a synchronous generator and a wind turbine, wherein the machine-side converter is connected to the grid-side converter and the synchronous generator, the synchronous generator rotor is connected to the wind turbine through a mechanical shaft, the wind turbine rotates under the drive of the wind, and the synchronous generator rotor is driven to rotate and generate electricity through the mechanical shaft; The machine-side model building unit is specifically used to build a small signal model of the machine-side converter, which specifically includes: building a small signal model of the machine-side converter current command value function; building a small signal model of the machine-side converter current inner loop control with the machine-side converter current command value as input; building a small signal model of the rotor shaft system between the synchronous generator and the wind turbine considering low-frequency dynamics, which specifically includes: building a small signal model of the mechanical torque inner loop of the wind turbine; building a small signal model of the electromagnetic torque inner loop of the synchronous generator; building a shaft system double-mass block model and describing the transmission relationship between the wind turbine and the synchronous generator; building a small signal model generated by the electromagnetic torque command value of the synchronous generator and the pitch angle command value of the wind turbine, which describes the small signal model of the control outer loop of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

[0095] In the embodiment of the present invention, the torsional vibration modal analysis module includes a calculation processing unit and a mapping relationship acquisition unit; A calculation processing unit is used to convert the state matrix generated by normalizing the state space equation of the shaft system based on the dual-mass block model of the shaft system into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode; specifically, it is used to normalize the state space equation of the shaft system based on the dual-mass block model of the shaft system to generate a state matrix; diagonalize the normalized state matrix to extract the left and right eigenvectors to obtain a decoupled matrix; and calculate the gain, damping coefficient and oscillation frequency of each mode based on the decoupled matrix; The mapping relationship acquisition unit is used to obtain the mapping relationship between the actual torque angle mode and the decoupled torque angle mode, that is, to obtain the relationship between the port voltage and current signals of the network-type direct-drive fan and the torsional vibration of the direct-drive fan shaft system.

[0096] The shaft system torsional vibration estimation module is specifically used to measure the voltage and current signals of the grid node port equipped with the PMU measurement device when forced oscillation occurs; obtain the transfer function between different grid node ports by constructing the wind farm s-domain node admittance matrix, and calculate the voltage and current signals of the grid-type direct-drive wind turbine port based on the measured voltage and current signals, and use the calculated voltage and current signals as the input of the small signal model of the grid-type direct-drive wind turbine to calculate the electromagnetic power small signal of the grid-type direct-drive wind turbine port; construct the electromagnetic power small signal of the grid-type direct-drive wind turbine port and the electromagnetic torque of the synchronous generator The electromagnetic torque of the synchronous generator is calculated based on the transfer function relationship between the small signal and the small signal of the mechanical speed of the synchronous generator rotor, combined with the electromagnetic power at the port of the meshed direct-drive wind turbine; the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine is constructed, and the mechanical torque of the wind turbine is calculated based on the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine; the magnitude of the torsional vibration of the shaft system of the meshed direct-drive wind turbine is calculated based on the mapping relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine combined with the actual torque angle mode and the decoupled torque angle mode.

[0097] An embodiment of the present invention further provides an electronic device, comprising: a processor, a communication interface, a memory and a communication bus, wherein the processor, the communication interface and the memory communicate with each other via the communication bus. The communication bus can be used for information transmission between the electronic device and the sensor. The processor can call the logic instructions in the memory to execute the following method: Step 1: construct a small signal model of a meshed direct-drive wind turbine; Step 2: based on the dual-mass block model of the shaft system, derive the relationship between the port voltage and current signals of the meshed direct-drive wind turbine and the torsional vibration of the shaft system of the meshed direct-drive wind turbine when forced oscillation occurs, wherein the dual-mass block includes a generator mass block and a turbine mass block; Step 3: when forced oscillation occurs, by constructing an s-domain node admittance model of the wind farm, the transfer function between different grid node ports is obtained, thereby calculating the required grid node port voltage and current signals, that is, the port voltage and current signals of the meshed direct-drive wind turbine, and using the calculated voltage and current signals as the input of the small signal model of the meshed direct-drive wind turbine, and combining the relationship between the port voltage and current signals of the meshed direct-drive wind turbine and the torsional vibration of the shaft system of the meshed direct-drive wind turbine to calculate the torsional vibration of the shaft system of the meshed direct-drive wind turbine caused by the forced oscillation.

[0098] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

[0099] An embodiment of the present invention provides a non-transitory computer-readable storage medium, which stores computer instructions, and the computer instructions enable the computer to execute the method provided by the above method embodiment, for example, including: Step 1: constructing a small signal model of a meshed direct-drive wind turbine; Step 2: based on a dual-mass block model of the shaft system, deriving the relationship between the port voltage and current signals of the meshed direct-drive wind turbine and the torsional vibration of the shaft system of the meshed direct-drive wind turbine when forced oscillation occurs, wherein the dual-mass block includes a generator mass block and a turbine mass block; Step 3: when forced oscillation occurs, by constructing an s-domain node admittance model of a wind farm, a transfer function between different grid node ports is obtained, thereby calculating the required grid node port voltage and current signals, that is, the port voltage and current signals of the meshed direct-drive wind turbine, and using the calculated voltage and current signals as inputs of the small signal model of the meshed direct-drive wind turbine, and combining the relationship between the port voltage and current signals of the meshed direct-drive wind turbine and the torsional vibration of the shaft system of the meshed direct-drive wind turbine to calculate the torsional vibration of the shaft system of the meshed direct-drive wind turbine caused by the forced oscillation.

[0100] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0101] An embodiment of a torsional vibration prediction device for a meshed direct-drive fan provided in an embodiment of the present invention belongs to the same inventive concept as the torsional vibration prediction method for a meshed direct-drive fan in the above-mentioned embodiments. For details not fully described in the embodiment of the torsional vibration prediction device for a meshed direct-drive fan, reference can be made to the embodiment of the above-mentioned torsional vibration prediction method for a meshed direct-drive fan.

[0102] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A method for predicting torsional vibration of a grid-type direct-drive fan, characterized in that: The steps include: Construct a small signal model of a grid-type direct-drive wind turbine; Based on the shaft double mass model, the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine when forced oscillation occurs is derived. The double mass includes the generator mass and the turbine mass. When forced oscillation occurs, the transfer function between different grid node ports is obtained by constructing the s-domain node admittance model of the wind farm, so as to calculate the required grid node port voltage and current signals, that is, the port voltage and current signals of the grid-type direct-drive wind turbine. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine caused by forced oscillation is calculated based on the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the shaft system of the grid-type direct-drive wind turbine.

2. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 1, characterized in that: The steps to construct a small signal model of a grid-type direct-drive wind turbine include: Construct a small signal model of the grid-side converter of a grid-connected direct-drive wind turbine; Construct a small signal model of the grid-type direct-drive wind turbine side; The grid-side converter small signal model of the grid-type direct-drive wind turbine is combined with the small signal model of the grid-type direct-drive wind turbine side in series to form a complete small signal model of the grid-type direct-drive wind turbine.

3. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 2, characterized in that: The steps of constructing the small signal model of the grid-side converter of the grid-connected direct-drive wind turbine include: Constructing the state equation of the power loop, specifically including: constructing the state equation of the first-order low-pass link and performing linear processing; constructing the state equation of the active power link and performing linear processing; constructing the state equation of the reactive power link and performing linear processing; Construct the voltage and current double closed loop state equation and perform linearization processing; Construct the state equation of the filter circuit and perform linearization; Integrate and construct the power loop, voltage and current double closed loops, and the state equation of the filter circuit; The integrated state equation is converted into a small signal equation to obtain the small signal model of the grid-side converter of the grid-connected direct-drive wind turbine.

4. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 2, characterized in that: The machine-side structure of the grid-type direct-drive wind turbine includes a machine-side converter, a synchronous generator and a wind turbine, wherein the machine-side converter is connected to the grid-side converter and the synchronous generator, the synchronous generator rotor is connected to the wind turbine through a mechanical shaft, the wind turbine rotates under the drive of the wind, and the synchronous generator rotor is driven to rotate and generate electricity through the mechanical shaft; The steps of constructing a small signal model of a grid-type direct-drive wind turbine include: Constructing a small signal model of the machine-side converter, specifically including: constructing a small signal model of the current command value function of the machine-side converter; constructing a small signal model of the current inner loop control of the machine-side converter with the current command value of the machine-side converter as input; Construct a small signal model of the rotor shaft system between the synchronous generator and the wind turbine considering low-frequency dynamics, specifically including: constructing a small signal model of the mechanical torque inner loop of the wind turbine; constructing a small signal model of the electromagnetic torque inner loop of the synchronous generator; constructing a shaft system double-mass block model and describing the transmission relationship between the wind turbine and the synchronous generator; A small signal model generated by the electromagnetic torque command value of the synchronous generator and the pitch angle command value of the wind turbine is constructed, which describes the small signal model of the control outer loop of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

5. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 4, characterized in that: Based on the shaft double mass model, the steps of deriving the relationship between the port voltage and current signals of the grid-type direct-drive fan and the torsional vibration of the shaft system of the grid-type direct-drive fan when forced oscillation occurs include: The state matrix generated by normalizing the shaft system state space equation based on the shaft system dual-mass block model is converted into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode, and the mapping relationship between the actual torque angle mode and the decoupled torque angle mode is obtained, that is, the relationship between the port voltage and current signals of the grid-type direct-drive fan and the torsional vibration of the shaft system of the grid-type direct-drive fan is obtained.

6. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 5, characterized in that: The steps of converting the state matrix generated by normalizing the state space equation of the shaft system based on the shaft system double mass model into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode include: Normalize the state space equation of the shaft system based on the shaft system double mass model to generate a state matrix; Diagonalize the normalized state matrix to extract the left and right eigenvectors and obtain the decoupled matrix; The gain, damping coefficient and oscillation frequency of each mode are calculated based on the decoupled matrix.

7. The method for predicting torsional vibration of a grid-type direct-drive wind turbine according to claim 4, characterized in that: When forced oscillation occurs, the transfer function between different grid node ports is obtained by constructing the wind farm s-domain node admittance model, thereby calculating the required grid node port voltage and current signals, that is, the grid-type direct-drive wind turbine port voltage and current signals, and using the calculated voltage and current signals as inputs of the small signal model of the grid-type direct-drive wind turbine. The steps of calculating the grid-type direct-drive wind turbine shaft system torsional vibration caused by forced oscillation in combination with the relationship between the grid-type direct-drive wind turbine port voltage and current signals and the grid-type direct-drive wind turbine shaft system torsional vibration include: When forced oscillation occurs, the voltage and current signals of the power grid node ports equipped with PMU measurement equipment are measured; The transfer function between different grid node ports is obtained by constructing the wind farm s-domain node admittance matrix, and the voltage and current signals of the grid-type direct-drive wind turbine ports are calculated based on the measured voltage and current signals. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine to calculate the electromagnetic power small signal of the grid-type direct-drive wind turbine ports. Constructing a transfer function relationship between the electromagnetic power small signal of the meshed direct-drive wind turbine port, the electromagnetic torque small signal of the synchronous generator, and the mechanical speed small signal of the synchronous generator rotor, and calculating the electromagnetic torque of the synchronous generator in combination with the electromagnetic power of the meshed direct-drive wind turbine port; constructing a transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine, and calculating the mechanical torque of the wind turbine in combination with the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine; The magnitude of the torsional vibration of the grid-type direct-drive wind turbine shaft system is calculated based on the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine, combined with the mapping relationship between the actual torque angle mode and the decoupled torque angle mode.

8. A torsional vibration prediction device for a grid-type direct-drive fan, characterized in that: It includes model building module, torsional vibration modal analysis module and shaft torsional vibration estimation module; Model building module, used to build a small signal model of a grid-type direct-drive wind turbine; The torsional vibration modal analysis module is used to derive the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the torsional vibration of the grid-type direct-drive wind turbine shaft system when forced oscillation occurs based on the dual-mass model of the shaft system, wherein the dual-mass model includes a generator mass block and a turbine mass block; The shaft torsional vibration estimation module is used to obtain the transfer function between different grid node ports by constructing the wind farm s-domain node admittance model when forced oscillation occurs, so as to calculate the required grid node port voltage and current signals, that is, the port voltage and current signals of the grid-type direct-drive wind turbine. The calculated voltage and current signals are used as the input of the small signal model of the grid-type direct-drive wind turbine, and the shaft torsional vibration of the grid-type direct-drive wind turbine caused by forced oscillation is calculated by combining the relationship between the port voltage and current signals of the grid-type direct-drive wind turbine and the shaft torsional vibration of the grid-type direct-drive wind turbine.

9. An electronic device, characterized in that: The electronic device includes: at least one processor; and a memory communicatively connected to the at least one processor; the memory stores computer program instructions executable by the at least one processor, and the computer program instructions are executed by the at least one processor so that the at least one processor can execute the torsional vibration prediction method of a grid-type direct-drive wind turbine as described in any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium stores computer instructions, and the computer instructions enable the computer to execute the torsional vibration prediction method of a grid-type direct-drive wind turbine according to any one of claims 1 to 7.

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