A network-constructed direct-drive wind turbine torsional vibration prediction method, device, equipment and storage medium

Abstract

The present application belongs to the technical field of fan torsional vibration prediction, and particularly relates to a grid-connected direct-drive fan torsional vibration prediction method, device, equipment and storage medium. The method comprises: constructing a small signal model of the grid-connected direct-drive fan; based on a shafting double-mass block model, deducing the relationship between the port voltage and current signals of the direct-drive fan and the torsional vibration of the shafting of the direct-drive fan when forced oscillation occurs; when forced oscillation occurs, by constructing a wind farm s-domain node admittance model, the transfer function between different grid node ports is obtained, so as to calculate the required grid node port voltage and current signals, taking the calculated voltage and current signals as the input of the small signal model of the grid-connected direct-drive fan, and combining the relationship between the port voltage and current signals of the grid-connected direct-drive fan and the torsional vibration of the shafting of the grid-connected direct-drive fan to calculate the torsional vibration of the shafting of the grid-connected direct-drive fan caused by forced oscillation. It is helpful to timely find and handle potential torsional vibration problems and avoid the occurrence of faults.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wind turbine torsional vibration prediction, and particularly relates to a grid-connected direct-drive wind turbine torsional vibration prediction method, device, equipment and storage medium. BACKGROUND

[0002] There is always a small disturbance in a power system, and more and more low-frequency oscillations are proved not to be caused by insufficient damping, but by forced oscillation caused by persistent and periodic small disturbances in the system. Generally speaking, when there is a periodic disturbance 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 disturbance.

[0003] When the frequency of external periodic disturbance is close to the natural frequency of the system, even if the system damping is positive, the external resonance phenomenon may occur. The external resonance may cause large-scale power oscillation and frequency and voltage fluctuation of the system. The previous research on grid-connected new energy mainly focuses on the negative damping free oscillation problem of grid-following equipment in a weak grid scenario. Literature shows that grid-forming equipment still has a high stability margin in a weak grid scenario. However, these studies do not discuss the influence on the safe operation of grid-forming equipment when forced oscillation occurs in a weak grid scenario. When external resonance caused by forced oscillation occurs, the frequency and voltage fluctuation of the power grid may cause the grid-forming equipment to be unstable or even off-grid. When the grid-forming equipment contains a mechanical shaft, the 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 oscillation, and forced oscillation may cause external resonance phenomenon under certain conditions (such as when the frequency of external disturbance is close to the natural frequency of the system), which seriously threatens the frequency, voltage and safe operation of grid-forming equipment. SUMMARY

[0005] In view of the problem that when the grid-forming equipment contains a mechanical shaft, the external resonance may cause shaft torsional vibration, which seriously threatens the safe operation of the equipment, the application provides a grid-connected direct-drive wind turbine torsional vibration prediction method, device, equipment and storage medium.

[0006] In the first aspect, the application provides a grid-connected direct-drive wind turbine torsional vibration prediction method, which includes the following steps:

[0007] Constructing a small signal model of the grid-connected direct-drive wind turbine;

[0008] Based on a shaft system double-mass block model, the relationship between the port voltage and current signals of the grid-connected direct-drive wind turbine and the shaft system torsional vibration of the grid-connected direct-drive wind turbine when forced oscillation occurs is derived, wherein the double-mass block includes a generator mass block and a turbine mass block.

[0009] 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, i.e. the grid-connected direct-drive wind turbine port voltage and current signals. The calculated voltage and current signals are taken as the input of the small-signal model of the grid-connected direct-drive wind turbine, and the grid-connected direct-drive wind turbine shaft torsional vibration caused by forced oscillation is calculated in combination with the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration.

[0010] As a preferred embodiment of the present application, the step of constructing the small-signal model of the grid-connected direct-drive wind turbine includes:

[0011] constructing a grid-side converter small-signal model of the grid-connected direct-drive wind turbine;

[0012] constructing a machine-side small-signal model of the grid-connected direct-drive wind turbine;

[0013] combining the grid-side converter small-signal model of the grid-connected direct-drive wind turbine and the machine-side small-signal model of the grid-connected direct-drive wind turbine in series to form a complete small-signal model of the grid-connected direct-drive wind turbine.

[0014] As a preferred embodiment of the present application, the step of constructing the grid-side converter small-signal model of the grid-connected direct-drive wind turbine includes:

[0015] constructing a state equation of the power loop, specifically including: constructing a state equation of a first-order low-pass link and performing linearization processing; constructing a state equation of an active power link and performing linearization processing; and constructing a state equation of a reactive power link and performing linearization processing;

[0016] constructing a state equation of the voltage and current double-closed loop and performing linearization processing;

[0017] constructing a state equation of the filter circuit and performing linearization processing;

[0018] integrating the constructed state equations of the power loop, the voltage and current double-closed loop, and the filter circuit;

[0019] converting the integrated state equation into a small-signal equation to obtain the grid-side converter small-signal model of the grid-connected direct-drive wind turbine.

[0020] As a preferred embodiment of the present application, the machine side of the grid-connected 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 drags the synchronous generator rotor to rotate and generate electricity through the mechanical shaft; the step of constructing the machine-side small-signal model of the grid-connected direct-drive wind turbine includes:

[0021] The machine-side converter small signal model is constructed, specifically including: constructing a machine-side converter current instruction value function small signal model; constructing a machine-side converter current inner loop control small signal model with the machine-side converter current instruction value as input;

[0022] A small signal model of a rotor shaft system between the synchronous generator and the wind turbine considering low-frequency dynamics is constructed, specifically including: constructing a small signal model of a mechanical torque inner loop of the wind turbine; constructing a small signal model of an electromagnetic torque inner loop of the synchronous generator; constructing a shaft system double-mass block model and describing a transmission relationship between the wind turbine and the synchronous generator;

[0023] A small signal model of synchronous generator electromagnetic torque instruction value and wind turbine pitch angle instruction value generation is constructed, which describes a small signal model of a control outer loop of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

[0024] As a preferred technical scheme of the present application, the step of deducing the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration when forced oscillation occurs based on the shaft system double-mass block model includes:

[0025] The state matrix generated by normalizing the shaft system state space equation based on the shaft system double-mass block model is made 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 grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration is obtained.

[0026] As a preferred technical scheme of the present application, the step of making the state matrix generated by normalizing the shaft system state space equation based on the shaft system double-mass block model into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode includes:

[0027] The shaft system state space equation based on the shaft system double-mass block model is normalized to generate a state matrix;

[0028] The normalized state matrix is diagonalized to extract left and right eigenvectors to obtain a decoupled matrix;

[0029] The gain, damping coefficient and oscillation frequency of each mode are calculated based on the decoupled matrix.

[0030] As a preferred technical solution of the present application, 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-connected direct-drive wind turbine, the calculated voltage and current signals are taken as the input of the small signal model of the grid-connected direct-drive wind turbine, and the forced oscillation induced grid-connected direct-drive wind turbine shaft torsional vibration is calculated by combining the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration, and the steps include:

[0031] When forced oscillation occurs, the voltage and current signals of the grid node port equipped with a PMU measuring device are measured;

[0032] The transfer function between different grid node ports is obtained by constructing the s-domain node admittance matrix, and based on the measured voltage and current signals, the voltage and current signals of the grid-connected direct-drive wind turbine port are calculated, and the calculated voltage and current signals are taken as the input of the small signal model of the grid-connected direct-drive wind turbine, and the electromagnetic power small signal of the grid-connected direct-drive wind turbine port is calculated;

[0033] The transfer function relationship between the electromagnetic power small signal of the grid-connected direct-drive wind turbine port and the electromagnetic torque small signal of the synchronous generator and the mechanical speed small signal of the synchronous generator rotor is constructed, and the electromagnetic torque of the synchronous generator is calculated in combination with the electromagnetic power of the grid-connected direct-drive wind turbine port;

[0034] 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 in combination with the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine;

[0035] According to the mapping relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine and the actual torque angle mode and the decoupled torque angle mode, the size of the grid-connected direct-drive wind turbine shaft torsional vibration is calculated.

[0036] In a second aspect, the present application also provides a grid-connected direct-drive wind turbine torsional vibration prediction device, which comprises a model construction module, a torsional vibration mode analysis module and a shaft torsional vibration estimation module;

[0037] The model construction module is used to construct a small signal model of the grid-connected direct-drive wind turbine;

[0038] The torsional vibration mode analysis module is used to deduce the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration when forced oscillation occurs based on the shaft double mass block model, wherein the double mass block includes a generator mass block and a turbine mass block;

[0039] The shaft torsional vibration estimation module is configured to, when forced oscillation occurs, obtain the transfer function between different power grid node ports by constructing a wind farm s-domain node admittance model, so as to calculate the required power grid node port voltage and current signals, i.e., the grid-connected direct-drive wind turbine port voltage and current signals, take the calculated voltage and current signals as the input of the small-signal model of the grid-connected direct-drive wind turbine, and calculate the grid-connected direct-drive wind turbine shaft torsional vibration caused by forced oscillation in combination with the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration.

[0040] As a preferred technical solution of the present application, the model construction module comprises a grid-side model construction unit, a machine-side model construction unit and a connection unit.

[0041] The grid-side model construction unit is configured to construct a grid-side converter small-signal model of the grid-connected direct-drive wind turbine.

[0042] The machine-side model construction unit is configured to construct a machine-side small-signal model of the grid-connected direct-drive wind turbine.

[0043] The connection unit is configured to combine the grid-side converter small-signal model and the machine-side small-signal model of the grid-connected direct-drive wind turbine in series to form a complete small-signal model of the grid-connected direct-drive wind turbine.

[0044] As a preferred technical solution of the present application, the grid-side model construction unit is specifically configured to construct the state equation of the power loop, and specifically comprises: constructing the state equation of a first-order low-pass element and performing linearization processing; constructing the state equation of an active power element and performing linearization processing; constructing the state equation of a reactive power element and performing linearization processing; constructing the state equation of a voltage and current double-closed loop and performing linearization processing; constructing the state equation of a filter circuit and performing linearization processing; integrating the constructed state equations of the power loop, the voltage and current double-closed loop and the filter circuit; and converting the integrated state equation into a small-signal equation to obtain the grid-side converter small-signal model of the grid-connected direct-drive wind turbine.

[0045] As a preferred technical solution of the present application, the machine-side structure of the grid-connected direct-drive wind turbine comprises 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 drags the synchronous generator rotor to rotate and generate electricity through the mechanical shaft.

[0046] The machine side model construction unit is specifically configured to construct a small signal model of the machine side converter, and specifically includes: constructing a small signal model of a current instruction value function of the machine side converter; constructing a small signal model of a current inner loop control of the machine side converter taking the current instruction value of the machine side converter as input; constructing a small signal model of a rotor shaft system between the synchronous generator and the wind turbine considering low frequency dynamics, specifically including: constructing a small signal model of a mechanical torque inner loop of the wind turbine; constructing a small signal model of an electromagnetic torque inner loop of the synchronous generator; constructing a shaft system double mass block model and describing a transmission relationship between the wind turbine and the synchronous generator; constructing a small signal model of electromagnetic torque instruction values of the synchronous generator and pitch angle instruction values of the wind turbine, which describes a control outer loop small signal model of the mechanical torque of the wind turbine and the electromagnetic torque of the synchronous generator.

[0047] As a preferred technical scheme of the present application, the torsional vibration mode analysis module comprises a calculation processing unit and a mapping relationship acquisition unit.

[0048] The calculation processing unit is configured to normalize a state matrix generated by an axial system state space equation based on the axial system double mass block model to make the state matrix into a diagonal matrix, so as to extract gain, damping coefficient and oscillation frequency of each mode; specifically configured to generate a state matrix by normalizing the axial system state space equation based on the axial system double mass block model; diagonalize the normalized state matrix to extract left and right eigenvectors and obtain a decoupled matrix; and calculate gain, damping coefficient and oscillation frequency of each mode based on the decoupled matrix.

[0049] The mapping relationship acquisition unit is configured to obtain a mapping relationship between an actual torque angle mode and a decoupled torque angle mode, i.e., a relationship between a grid-connected direct-drive wind turbine port voltage and current signal and a direct-drive wind turbine axial system torsional vibration.

[0050] As a preferred technical scheme of the present application, the shaft torsional vibration estimation module is specifically used for measuring voltage and current signals of a power grid node port provided with a PMU measurement device when forced oscillation occurs; a transfer function between different power grid node ports is obtained by constructing a wind farm s-domain node admittance matrix, and voltage and current signals of a grid-connected direct-drive wind turbine port are calculated based on the measured voltage and current signals, the calculated voltage and current signals are taken as inputs of a small-signal model of the grid-connected direct-drive wind turbine, and a small-signal electromagnetic power of the grid-connected direct-drive wind turbine port is calculated; a transfer function relationship between the small-signal electromagnetic power of the grid-connected direct-drive wind turbine port and a small-signal electromagnetic torque of a synchronous generator and a small-signal mechanical rotating speed of a rotor of the synchronous generator is constructed, and the electromagnetic torque of the synchronous generator is calculated in combination with the small-signal electromagnetic power of the grid-connected direct-drive wind turbine; a transfer function relationship between the electromagnetic torque of the synchronous generator and a mechanical torque of the wind turbine is constructed, and the mechanical torque of the wind turbine is calculated in combination with the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine; and the magnitude of the shaft torsional vibration of the grid-connected direct-drive wind turbine is calculated according to the mapping relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine and the actual torsional angle mode and the decoupled torsional angle mode.

[0051] In a third aspect, the present application also provides an electronic device, which comprises at least one processor and a memory connected with 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 to enable the at least one processor to execute the grid-connected direct-drive wind turbine torsional vibration prediction method according to the first aspect.

[0052] In a fourth aspect, the present application also provides a non-transitory computer readable storage medium storing computer instructions, and the computer instructions enable the computer to execute the grid-connected direct-drive wind turbine torsional vibration prediction method according to the first aspect.

[0053] As can be seen from the above technical scheme, the present application has the following advantages: by constructing a small-signal model of the grid-connected direct-drive wind turbine, the method can accurately reflect the small-signal transfer relationship between the wind turbine shaft and the port voltage and current, thereby greatly improving the accuracy of the prediction of the torsional vibration of the direct-drive wind turbine shaft.

[0054] In combination with the established small-signal model, the method can monitor the forced oscillation phenomenon in the wind farm system in real time. By constructing an s-domain node admittance model of the wind farm system, the transfer function between different ports can be conveniently obtained, and then when the forced oscillation occurs, the torsional vibration of the wind turbine shaft can be quickly calculated by measuring the voltage and current signals of the port, thereby avoiding the occurrence of faults.

[0055] This method not only can predict the torsional vibration of direct drive wind turbine shafting, but also can provide strong support for the operation and maintenance of wind farm. Through real-time monitoring and early warning, wind farm operators can timely understand the running state of the wind turbine, and adjust the operation strategy according to the actual situation, so as to optimize the overall performance of the wind farm. At the same time, it provides a scientific basis for regular maintenance and repair of the wind turbine, reduces maintenance cost, and prolongs the service life of the equipment. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to make the technical solutions in the present application or the prior art clearer, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0057] Figure 1 is a schematic flow chart of the method of an embodiment of the present application.

[0058] Figure 2 is a schematic diagram of a networked direct drive wind turbine.

[0059] Figure 3 is a VSG power loop control block diagram.

[0060] Figure 4 is a working state diagram under different wind speeds, a torque control and a pitch angle control schematic diagram.

[0061] Figure 5 is an estimated value of shaft torsional vibration caused by disturbance under the conditions of wind speeds of 11.5 m / s, 11.7 / s and 12 m / s.

[0062] Figure 6 is a voltage, current, electromagnetic torque disturbance and torsional vibration disturbance diagram of the system after applying load impact at 5s.

[0063] Figure 7 is a comparison diagram of system torsional vibration waveform and theoretical estimation waveform after applying load impact at 5s.

[0064] Figure 8 is a schematic block diagram of the device of an embodiment of the present application. DETAILED DESCRIPTION

[0065] In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the present application.

[0066] As Figure 1 shown, the embodiment of the application provides a torsional vibration prediction method for grid-connected direct-driven wind turbines, comprising:

[0067] Step 1: Constructing a small signal model of the grid-connected direct-driven wind turbine;

[0068] The grid-connected direct-driven wind turbine adopts virtual synchronous generator (VSG) control. The following describes a small signal modeling process considering mechanical dynamics: The schematic diagram of the grid-connected direct-driven wind turbine is shown in Figure 2 The grid-connected direct-driven wind turbine body includes a wind turbine, a synchronous generator (PMSG), a machine-side converter (MSC), a grid-side converter (GSC), and a filter circuit, and the resistance Rg and the inductance Lg constitute the filter.

[0069] The wind turbine body mainly adopts pitch angle control, and the pitch angle command value is subtracted from the actual pitch angle , and the pitch angle dynamics are controlled through the transfer function to output .

[0070] The machine-side converter (MSC) adopts constant DC bus control, and the control thereof adopts constant DC bus voltage control. The control input is the difference between the collected DC bus voltage and the bus voltage command value , and the DC bus voltage and are obtained after the PI link, and are input to the current inner loop, wherein is controlled to be 0. The machine-side converter voltages and are obtained after the current loop inner loop control, and are then input to the machine-side converter (MSC).

[0071] The active power link of the grid-side converter (GSC) control adopts virtual synchronous generator control, and the input is the difference between the active power command value and the active power , and the output is the power loop phase angle after the virtual synchronous link composed of the device inertia , the droop coefficient , and the damping coefficient . The reactive power link adopts droop control, and the input is the difference between the d-axis voltage command value and the measured d-axis , and the power loop phase angle is obtained after the PI link.The output reference voltage is synthesized and taken as the input of the voltage-current double closed loop control, the output of which is transformed by dq / abc and input into the grid-side converter GSC through space vector pulse width modulation (SVPWM).

[0072] Figure 3 The virtual synchronous machine in the power loop and the reactive power droop control are respectively shown, and the input is the grid-connected point voltage and current , and the active power and reactive power are obtained after power calculation, and are input into the filter and output and according to formulas (1) and (2), and are input into the virtual synchronous machine link and the reactive power droop link respectively, wherein 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).

[0073] Grid-side converter impedance 1.1 power loop

[0074] 1) First-order low-pass link

[0075] The state equation of the first-order low-pass link is shown in formulas (1) and (2);

[0076] (1)

[0077] (2)

[0078] In the formulas, and respectively represent the active power and reactive power output from the converter to the grid-connected point. represents the Laplace operator. and respectively represent the grid-connected point output voltage and current in the dq coordinate system. represents the system power frequency angular velocity, which is 50 Hz by default here, which is the rated frequency.

[0079] 2) Active power link

[0080] The state equation of the active power link is shown in formula (3);

[0081] (3)

[0082] In the formula, represents the active power command value, represents the virtual angular frequency of the grid-forming device, represents the device inertia, represents the droop coefficient, Virtual damping coefficient controlled by VSG.

[0083] After linearization, we get:

[0084] (4)

[0085] 3) Reactive power loop

[0086] The state equation of the reactive power loop is shown in equations (5) and (6).

[0087] (5)

[0088] (6)

[0089] In the formula represents the dq voltage command value of the grid-connected point output, represents the reactive droop coefficient, represents the reactive power command value, and represents the reactive power output of the grid-connected point.

[0090] After linearization, we get: , ;

[0091] The above equations (3), (4), (7), and (8) are unified as a state space equation:

[0092] (9)

[0093] where 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 constitute the output matrix.

[0094] The specific expressions of each matrix are as follows:

[0095]

[0096]

[0097] 1.2 Voltage and current double closed loop

[0098] The voltage loop is represented as:

[0099] (10)

[0100] where is the voltage loop input, is the output reference voltage of the power loop.

[0101] (11)

[0102] wherein is the inductor current command value of the voltage loop output. and respectively represent the PI parameters of the current loop, represents the parallel ground capacitor.

[0103] The current loop is represented as:

[0104] (12)

[0105] wherein is the current loop output.

[0106] (13)

[0107] wherein is the voltage command value of the current loop output, represents the inductor current, and respectively represent the PI parameters of the current loop, represents the filter inductor.

[0108] Equation (10) is linearized to obtain:

[0109] (14)

[0110] Equation (11) is linearized to obtain:

[0111] (15)

[0112] Equation (12) is linearized to obtain:

[0113] (16)

[0114] Equation (13) is linearized to obtain:

[0115] (17)

[0116] wherein is the state matrix of the voltage loop, , represents the voltage input matrix of the voltage loop, represents the output state matrix of the voltage loop, and represent the transfer function matrix of the voltage loop. is the state matrix of the current loop, , represents the input matrix of the current loop, The current loop output state matrix, The current loop transfer function matrix. The definitions of each part are as follows:

[0117] .

[0118] 1.3 Filter circuit loop

[0119] The output voltage and current loop of the grid-forming grid-side converter can be described in the form of equation (18):

[0120] (18)

[0121] In the formula: The dq-axis components of the inverter output bridge arm voltage, and The series resistance and filter inductance of the converter, respectively; The parallel ground capacitor.

[0122] After linearization, the state space model of the filter and grid output is obtained:

[0123] (19)

[0124] Where is the state matrix of the filter and series resistance loop, The input matrix of the filter and series resistance loop. The specific representation of each matrix is as follows:

[0125]

[0126]

[0127] (20)

[0128] 1.4 Integration of state equation and input-output equation

[0129]

[0130] Where, the power loop , the voltage and current double closed loop , the filter and series resistance ; the state variable , and are input and output quantities.

[0131] (21)

[0132] The definitions of each part are as follows:

[0133]

[0134]

[0135] The input is quantized to only The output is quantized to only ;

[0136] First, the matrix in equation (21) is split to get

[0137] (22)

[0138] (23)

[0139] (24)

[0140] By eliminating, finally let the formula contains only state variables and input and output .

[0141] Note that in the elimination process of the input-output equation, the following approximation is made: consider , because the delay link is ignored.

[0142] After elimination, the input-output equation expression is as follows:

[0143] (25)

[0144] Move to the other side to get:

[0145] (26)

[0146] (27)

[0147] Where .

[0148] 1.5 State space equation is converted into impedance

[0149] The state equation is written as follows:

[0150] (28)

[0151] Further split the B matrix into , the state equation is obtained:

[0152] (29)

[0153] After Laplace transformation, Thus, we get

[0154] (30)

[0155] Substitute equation (30) into the input equation, and finally get the admittance:

[0156] (31)

[0157] The admittance and impedance present an inverse relationship ;

[0158] Finally, we get the impedance of the grid-connected direct-driven wind turbine grid-side converter , which is the small-signal model of the grid-connected direct-driven wind turbine grid-side converter.

[0159] 2. Grid-connected direct-driven wind turbine machine-side modeling considering mechanical dynamics

[0160] 1.1 MSC impedance

[0161] 1) Current command value function

[0162] As shown in Figure 2 , the small-signal model of the grid-connected direct-driven wind turbine considering the current controller is as follows:

[0163] (32)

[0164] In the formula, represents the d-axis current command value, represents the machine-side electromagnetic torque, and the flux linkage relationship . Equation (32) shows that the d-axis current command value of the grid-connected direct-driven wind turbine is in direct proportion to the electromagnetic torque . The current command value of the q-axis is constant, which will make . Thus, the transfer function relationship of the current inner loop command value is:

[0165] (33)

[0166] In the formula, .

[0167] 2) Current inner loop control model

[0168] As shown in Figure 2 , the internal current control of MSC is similar to GSC, with one major difference being the angular frequency involving the dynamic behavior of decoupling term . The inductance is called the transient inductance of the rotor.

[0169] The input quantities of the inner current loop include the stator current control quantities and the command value from the voltage loop and the rotor electrical angular velocity .

[0170] (34)

[0171] where and denote the small signals of the rotor voltage, current control quantities, denote the rotor electrical angular velocity, and several impedance variables are defined as:

[0172] (35)

[0173] (36)

[0174] (37)

[0175] the rotor electrical angular velocity is directly related to the mechanical angular velocity , which will be further derived later.

[0176] 1.2 Rotor modeling considering mechanical low-frequency dynamics

[0177] The shaft system dynamic model of grid-connected direct-drive wind turbines will be described using a shaft system two-mass model and an electromagnetic torque function.

[0178] 1) Mechanical torque model of wind turbine

[0179] After considering the aerodynamic model of the wind turbine, as shown in Figure 2 , the small-signal model of the mechanical torque of the wind turbine is as follows:

[0180] (38)

[0181] where the small-signal variables are defined as follows, the mechanical torque of the wind turbine , the wind speed , the small-signal of the pitch angle , the small-signal of the mechanical angular velocity . The coefficients are defined as follows: denotes the air density, denotes the mechanical torque coefficient.

[0182] The dynamics of the pitch angle is determined by its command value:

[0183] (39)

[0184] where denotes the transfer function of the pitch angle regulation, command value indicative of the pitch angle.

[0185] 2) Electromagnetic torque model of the synchronous generator

[0186] The small-signal model of the electromagnetic torque is given by

[0187] (40)

[0188] where the small-signal of the electromagnetic torque is given by

[0189] (41)

[0190] (42)

[0191] where represents the small-signal of the electromagnetic torque, represents the small-signal of the stator current, and represents the small-signal of the rotor current.

[0192] 3) Transmission process between the wind turbine and the synchronous generator

[0193] The interaction between the mechanical torque and the electromagnetic torque influences the dynamics of the rotor speed together. By modeling the two-mass model, we have

[0194] (43)

[0195] (44)

[0196] (45)

[0197] where describes the moment of inertia of the wind turbine mass, and describes the moment of inertia of the generator mass dragged by the wind turbine. , , and represent the damping and stiffness coefficients of the two-mass model, which describe the flexible connection between the two masses. Among them represents the damping coefficient of the wind turbine shaft, represents the damping coefficient of the generator shaft, and represent the gain and damping coefficients of the flexible transmission chain connected between the two masses, respectively.

[0198] (46)

[0199] ​wherein is a state variable , is a transfer function between the rotor angular velocity and the electromagnetic torque ,

[0200] (47)

[0201] wherein depends on the drive shaft parameters, the wind speed and the turbine rotational speed .

[0202] 2.3 Generation of electromagnetic torque command value and pitch angle command value

[0203] The transmission relationship between the wind turbine and the synchronous generator is introduced in section 2.2. Here the control process of the input of the transmission system on both sides, the electromagnetic torque and the mechanical torque, is introduced. The grid-connected direct-drive wind turbine uses rotational speed command control, and the electromagnetic torque command value of the wind turbine is controlled by the mechanical rotational speed ; and the pitch angle command value is also controlled by the mechanical rotational speed . The mechanical rotational speed reflects the current wind speed and the working state of the operation mode of the grid-connected direct-drive wind turbine.

[0204] As shown in Fig. Figure 4 , the working state of the grid-connected direct-drive wind turbine is different at different wind speeds . (a) in Fig. Figure 4 indicates four regions of the grid-connected direct-drive wind turbine, the grid-connected direct-drive wind turbine is in the constant rotational speed state at the wind speed , works in the maximum power mode at the wind speed , is in the constant rotational speed state at the wind speed , and when the wind speed , the electromagnetic torque of the grid-connected direct-drive wind turbine generally no longer increases, at this time the grid-connected direct-drive wind turbine gradually transitions to the full load state. As described above, the pitch angle and the mechanical rotational speed of the grid-connected direct-drive wind turbine are different at different working states. Figure 4 (b) in Fig. indicates the details of the torque control, according to whether the rotational speed exceeds the average value of and , the transfer function of the torque output of the grid-connected direct-drive wind turbine is switched. When the grid-connected direct-drive wind turbine operates in the first to third modes, the torque control is started, and it is emphasized that according to whether the rotational speed exceeds the limitDeciding the torque output instruction value of grid-connected direct drive wind turbine Whether the output is 0, that is, whether the wind turbine enters the constant speed state. Figure 4 (c) in the above formula (46) represents the pitch angle control of the grid-connected direct drive wind turbine, wherein represents the transfer function of the pitch angle control.

[0205] In order to control the grid-connected direct drive wind turbine to meet the above operation rules, Figure 4 (b) and (c) in the above formula (46) represent that the electromagnetic torque instruction value and the pitch angle instruction value of the grid-connected direct drive wind turbine are controlled by the mechanical speed;

[0206] (48)

[0207] (49)

[0208] In the formula, represents the transfer function relationship between the mechanical speed of the grid-connected direct drive wind turbine and the electromagnetic torque instruction value, and represents the transfer function relationship between the mechanical speed of the grid-connected direct drive wind turbine and the pitch angle .

[0209] The transfer function of the pitch angle instruction value controlling the pitch angle is described by formula (49), so that the transfer function between the pitch angle and the mechanical speed is further obtained:

[0210] (50)

[0211] In the formula, represents the control transfer function of the pitch angle of the wind turbine. The transfer functions and in formula (49) and formula (50) are self-defined.

[0212] Substituting formula (50) into formula (46) and eliminating , the transfer function between the rotor angular speed of the synchronous generator and the electromagnetic torque can be obtained:

[0213] (51)

[0214] In the formula, is represented as follows:

[0215] (52)

[0216] 2.4 Overall modeling of grid-forming direct-drive wind turbine

[0217] 1) Stator converter impedance

[0218] From equation (31), the stator converter impedance of grid-forming control is :

[0219] (53)

[0220] 2) Rotor converter impedance

[0221] The rotor converter impedance can be described as

[0222] (54)

[0223] where , denote the stator-side and rotor-side impedance within the machine, respectively;

[0224] (55)

[0225] (56)

[0226] where and denote the resistance and inductance of the stator, respectively, and denotes the power frequency angular speed; denotes the inductance of the rotor of the machine.

[0227] and are specifically expressed in the following form:

[0228] (57)

[0229] (58)

[0230] Step 2: Based on the shafting double-mass block model, the relationship between the port voltage and current signals of the grid-forming direct-drive wind turbine and the torsional vibration of the shafting of the grid-forming direct-drive wind turbine when forced oscillation occurs is derived.

[0231] Since the shafting state equation matrix of the multi-mass block is not a diagonal matrix, it is not convenient to intuitively measure the torsional vibration degree of the direct-drive wind turbine shafting, so for a multi-mass block shafting, the shafting needs to be decoupled first, that is, the normalized state matrix of the shafting state space equation is made into a diagonal matrix, and then the gain, damping coefficient and oscillation frequency of each mode are extracted.

[0232] (59)

[0233] The variable definitions that need to be pointed out in the formula include: represents the angular displacement of the wind turbine mass block, and represents the angular displacement of the generator mass block.

[0234] The matrix diagonalization (decoupling) is performed on formula (59), and the specific decoupling process is as follows:

[0235] First, the moment of inertia matrix is diagonalized to extract the left and right eigenvectors , and the decoupled matrix is obtained;

[0236] (60)

[0237] The matrix and matrix are further processed by the vector . Since there is a transmission chain damping coefficient , diagonalization cannot be achieved. In combination with the actual parameters, it is considered that the off-diagonal term is small and can be approximately processed as diagonalization:

[0238] (61)

[0239] After diagonalization, only one item is left in the N matrix, because the mass block model generally contains N -1 gain coefficient after decoupling.

[0240] (62)

[0241] (63)

[0242] The double-mass block matrix only contains two modes, and the gain, damping, and angular frequency of each mode are calculated as follows:

[0243] (64)

[0244] (65)

[0245] (66)

[0246] After diagonalization, the electromagnetic torque mode and the shaft torsion angle mode of the double-mass block model can be represented by the classical second-order transfer function model of formula (67):

[0247] (67)

[0248] Actual torque angular mode and The following mapping relationship exists between the (wind turbine mass block and generator mass block) and the decoupled torque angular mode:

[0249] (68)

[0250] Step 3: When forced oscillation occurs, by constructing the nodal admittance model of the wind farm in the s-domain, the transfer function between different grid node ports is obtained, thereby calculating the required grid node port voltage and current signals, i.e., 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. Combining 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, the torsional vibration of the shaft system of the grid-type direct-drive wind turbine caused by forced oscillation is calculated.

[0251] The nodal admittance matrix of a wind farm in the s-domain can be described as follows:

[0252] (69)

[0253] In the formula The small-signal matrices representing the voltage and current at each node are denoted by , while the s-domain node impedance / admittance matrices are denoted by . It consists of a 2×2 dq impedance / admittance matrix for each device.

[0254] When forced oscillations occur 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 in other words...) (The determinant has no positive zeros). Once forced oscillation occurs, oscillations will still be measured at various points in the system. After the oscillations propagate through the system, their amplitude and phase will change. This change is determined by the overall impedance characteristics of the system.

[0255] Safety control of grid-connected wind turbines is particularly important in response to external power fluctuations, especially in strong power grids. Forced power oscillations can easily cause drastic changes in the power loop, unlike traditional grid-connected equipment. When significant power disturbances caused by forced oscillations occur, the grid control output changes rapidly. These rapid power output fluctuations from the grid side are transmitted to the rotor side via the bus capacitor, inducing shaft torsional vibration. Severe torsional vibration can seriously threaten equipment safety. Therefore, when forced power oscillations occur in the system, it is essential to prioritize shaft torsional vibration safety for grid-connected direct-drive wind turbines.

[0256] When forced oscillation occurs, the torsional vibration of the fan shaft system can be calculated by measuring the voltage and current signals at the port. The specific process is as follows:

[0257] The transfer function relationship between the electromagnetic power small signal of the grid-connected direct-drive wind turbine port and the synchronous generator electromagnetic torque small signal and the synchronous generator mechanical speed small signal is:

[0258] (70)

[0259] Substituting equation (51) into equation (70) gives:

[0260] (71)

[0261] Obviously, The voltage and current small signals at the grid node port measured by the PMU device installed can be obtained:

[0262] (72)

[0263] Substituting equation (51) into equation (38) gives:

[0264] (73)

[0265] where describes the transfer function relationship between the electromagnetic torque of the synchronous generator and the wind turbine mechanical torque . Among them is expressed as follows:

[0266] (74)

[0267] After obtaining and , the torsional vibration can be calculated by equation (67), and the natural torsional vibration and can be restored by equation (68).

[0268] According to the shaft system torque calculation method proposed in equation (67), the size of the shaft system torsional vibration can be estimated.

[0269] Specifically, a system composed 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 power grid through a 13.8KV / 230KV step-up substation; the wind farm contains 25 identical, rated voltage 690V, rated capacity of 2.5MW direct-drive wind turbine generators, which are connected in parallel through a collection 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 through a 220KV transmission line.

[0270] First, the s-domain dq admittance matrix of the system is listed as shown in equation (69), the transfer functions between different ports can be obtained, and 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 far right side of the figure) the voltage and current disturbance signals at the grid-connected point of the grid-connected direct-drive wind turbine during the accident 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-connected direct-drive wind turbine to be predicted.

[0271] Figure 5 is the estimated value of the shaft torsional vibration caused by the disturbance under the conditions of wind speeds of 11.5m / s, 11.7 / s and 12m / s. After calculation, the torque is different under different wind speed conditions after the system is disturbed at 5s. The high-cycle fatigue limit of the shaft section of the grid-connected direct-drive wind turbine is 1pu, and the pre-warning limit is selected as 0.8pu according to its 80% margin. At 12m / s, the system has already lost stability, and the increasing torque will destroy the shaft of the direct-drive wind turbine, and there is no doubt that the system is not safe at this time. At 11.5m / s, the system is still in a stable state, and the torque does not break through the fatigue limit for a long time, and is considered to be safe. At a wind speed of 11.7m / s, although the system is still in a stable state and the oscillation is in a decaying state according to the pole judgment, the shaft has broken through the pre-warning value for more than 10s, and the shaft is in a high fatigue loss state, which will trigger the shaft protection.

[0272] By adding a load at 5s, the system will cause oscillation. The theoretical calculation results are not verified, and the SCR in the model designed in this paper is 1.66, and the wind speed is 11.7m / s. The voltage and current at the grid-connected point of the wind farm where the oscillation occurs, and the electromagnetic torque disturbance of the grid-connected direct-drive wind turbine and the torsional vibration disturbance are shown in Figure 6 .

[0273] As shown in Figure 7As shown, the red line represents the simulation model under disturbance, the torsional vibration waveform is complex, the transient process of the first 5s is slightly different from the theoretical estimated waveform, which is caused by the calculation error when calculating the aggregate impedance by ignoring the non-dominant zero and pole. After 5s, the system actual torsional vibration and the theoretical torsional vibration amplitude are almost the same; the error between the simulation value and the estimated value of the oscillation frequency is not more than 0.1Hz, which is within the normal error range. Figure 7 It is shown that the torsional vibration of the direct-drive wind turbine shaft can be accurately calculated under the condition of known system impedance.

[0274] Through the above theoretical calculation and simulation, it is found that under the condition of system SCR=1.66 and wind speed of the wind farm of 11.7m / s, the system is in a stable state, but the shaft torsional vibration has triggered a warning, and the traditional impedance method ignores the shaft safety problem. This further shows that the small signal model of the direct-drive impedance considering the shaft dynamics and the operating point is of engineering guiding significance, and can provide theoretical support for system stability analysis and shaft safety analysis of the direct-drive unit.

[0275] As Figure 8 shown, the embodiment of the present application also provides a torsional vibration prediction device for grid-connected direct-drive wind turbine, comprising a model construction module, a torsional vibration modal analysis module and a shaft torsional vibration estimation module;

[0276] The model construction module is used to construct a small signal model of the grid-connected direct-drive wind turbine;

[0277] The torsional vibration modal analysis module is used to deduce the relationship between the port voltage and current signals of the grid-connected direct-drive wind turbine and the shaft torsional vibration of the grid-connected direct-drive wind turbine based on the shaft double-mass block model, wherein the double-mass block includes a generator mass block and a turbine mass block;

[0278] The shaft torsional vibration estimation module is used to, when the forced oscillation occurs, obtain the transfer functions between different grid node ports by constructing a s-domain node admittance model of the wind farm, so as to calculate the required grid node port voltage and current signals, i.e. the port voltage and current signals of the grid-connected direct-drive wind turbine, take the calculated voltage and current signals as the input of the small signal model of the grid-connected direct-drive wind turbine, and calculate the grid-connected direct-drive wind turbine shaft torsional vibration caused by the forced oscillation in combination with the relationship between the port voltage and current signals of the grid-connected direct-drive wind turbine and the shaft torsional vibration of the grid-connected direct-drive wind turbine.

[0279] In the embodiment of the present application, the model construction module comprises a grid-side model construction unit, a machine-side model construction unit and a connection unit;

[0280] The grid-side model construction unit is used to construct a grid-side converter small signal model of the grid-connected direct-drive wind turbine;

[0281] A machine side model construction unit is configured to construct a small signal model of a grid-connected direct-driven wind turbine machine side;

[0282] A connection unit is configured to combine the grid side converter small signal model of the grid-connected direct-driven wind turbine and the grid-connected direct-driven wind turbine side small signal model in series to form a complete small signal model of the grid-connected direct-driven wind turbine.

[0283] Specifically, the grid side model construction unit is specifically configured to construct a state equation of a power loop, and specifically includes: constructing a state equation of a first-order low-pass element and performing linearization processing; constructing a state equation of an active power element and performing linearization processing; constructing a state equation of a reactive power element and performing linearization processing; constructing a state equation of a voltage and current double closed loop and performing linearization processing; constructing a state equation of a filter circuit and performing linearization processing; integrating the constructed state equations of the power loop, the voltage and current double closed loop, and the filter circuit; and converting the integrated state equation into a small signal equation to obtain the grid side converter small signal model of the grid-connected direct-driven wind turbine.

[0284] The grid-connected direct-driven wind turbine machine side structure 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 drags the synchronous generator rotor to rotate and generate electricity through the mechanical shaft;

[0285] The machine side model construction unit is specifically configured to construct a machine side converter small signal model, and specifically includes: constructing a machine side converter current command value function small signal model; constructing a machine side converter current inner loop control small signal model with the machine side converter current command value as input; constructing a rotor shaft system small signal model between the synchronous generator and the wind turbine considering low frequency dynamics, specifically including: constructing a small signal model of a wind turbine mechanical torque inner loop; constructing a small signal model of a synchronous generator electromagnetic torque inner loop; constructing a shaft system double mass block model and describing a transmission relationship between the wind turbine and the synchronous generator; and constructing a small signal model of a synchronous generator electromagnetic torque command value and a wind turbine pitch angle command value, which describes a control outer loop small signal model of the wind turbine mechanical torque and the synchronous generator electromagnetic torque.

[0286] In the embodiment of the present application, the torsional vibration modal analysis module includes a calculation processing unit and a mapping relationship acquisition unit.

[0287] The computing processing unit is configured to normalize a state matrix generated by an axis system state space equation based on an axis system double mass block model to make the state matrix into a diagonal matrix, so as to extract gain, damping coefficient and oscillation frequency of each mode; specifically, the computing processing unit is configured to generate a state matrix based on normalization of the axis system state space equation based on the axis system double mass block model; diagonalize the normalized state matrix, so as to extract left and right eigenvectors, and obtain a decoupled matrix; and based on the decoupled matrix, calculate the gain, damping coefficient and oscillation frequency of each mode.

[0288] The mapping relationship obtaining unit is configured to obtain a mapping relationship between an actual torque angle mode and a decoupled torque angle mode, that is, obtain a relationship between port voltage and current signals of the grid-connected direct-drive wind turbine and shaft torsional vibration of the direct-drive wind turbine.

[0289] The shaft torsional vibration estimation module is specifically configured to, when forced oscillation occurs, measure voltage and current signals of a grid node port provided with a PMU measurement device; obtain a transfer function between different grid node ports by constructing a wind farm s-domain node admittance matrix, and based on the measured voltage and current signals, calculate voltage and current signals of a port of the grid-connected direct-drive wind turbine, take the calculated voltage and current signals as inputs of a small signal model of the grid-connected direct-drive wind turbine, and calculate a small signal of electromagnetic power of the port of the grid-connected direct-drive wind turbine; construct a transfer function relationship between the small signal of electromagnetic power of the port of the grid-connected direct-drive wind turbine and a small signal of electromagnetic torque of a synchronous generator and a small signal of mechanical rotating speed of a rotor of the synchronous generator, combine the electromagnetic torque of the synchronous generator to calculate electromagnetic torque of the synchronous generator; construct a transfer function relationship between the electromagnetic torque of the synchronous generator and mechanical torque of the wind turbine, combine the transfer function relationship between the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine to calculate the mechanical torque of the wind turbine; and according to the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine, and the mapping relationship between the actual torque angle mode and the decoupled torque angle mode, calculate a size of shaft torsional vibration of the grid-connected direct-drive wind turbine.

[0290] The embodiment of the present application also 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 complete mutual communication through the communication bus. The communication bus can be used for information transmission between the electronic device and the sensor. The processor can call logical instructions in the memory to execute the following method: step 1, constructing a small signal model of the grid-connected direct-drive wind turbine; step 2, based on a shaft system double mass block model, deducing the relationship between the port voltage and current signals of the grid-connected direct-drive wind turbine and the shaft torsional vibration of the grid-connected direct-drive wind turbine when forced oscillation occurs, wherein the double mass block comprises a generator mass block and a turbine mass block; step 3, when forced oscillation occurs, the transfer function between different grid nodes is obtained by constructing an 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-connected direct-drive wind turbine, and the calculated voltage and current signals are taken as the input of the small signal model of the grid-connected direct-drive wind turbine, and the shaft torsional vibration of the grid-connected direct-drive wind turbine caused by forced oscillation is calculated in combination with the relationship between the port voltage and current signals of the grid-connected direct-drive wind turbine and the shaft torsional vibration of the grid-connected direct-drive wind turbine.

[0291] In addition, the logical instructions in the memory described above can be realized in the form of a software function unit and sold or used as an independent product, and can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or part of the technical solutions can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the method described in various embodiments of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a magnetic disk or an optical disk and various program code storage media.

[0292] The embodiment of the present application provides a non-transitory computer readable storage medium storing computer instructions, which causes a computer to execute the method provided by the method embodiment, for example, comprising: step 1, constructing a small signal model of a grid-connected direct-drive wind turbine; step 2, based on a shaft system double mass block model, deriving a relationship between a port voltage and current signal of the grid-connected direct-drive wind turbine and a shaft torsional vibration of the grid-connected direct-drive wind turbine when forced oscillation occurs, wherein the double mass block comprises a generator mass block and a turbine mass block; and step 3, when the forced oscillation occurs, obtaining a transfer function between different power grid node ports by constructing an s-domain node admittance model of a wind farm, so as to calculate the required power grid node port voltage and current signal, that is, the port voltage and current signal of the grid-connected direct-drive wind turbine, and taking the calculated voltage and current signal as an input of the small signal model of the grid-connected direct-drive wind turbine, and combining the relationship between the port voltage and current signal of the grid-connected direct-drive wind turbine and the shaft torsional vibration of the grid-connected direct-drive wind turbine to calculate the shaft torsional vibration of the grid-connected direct-drive wind turbine caused by the forced oscillation.

[0293] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0294] The embodiment of the grid-connected direct-drive wind turbine torsional vibration prediction device provided by the embodiment of the present application belongs to the same inventive concept as the grid-connected direct-drive wind turbine torsional vibration prediction method described above, and the details not described in the embodiment of the grid-connected direct-drive wind turbine torsional vibration prediction device can be referred to the embodiment of the grid-connected direct-drive wind turbine torsional vibration prediction method.

[0295] Although the present application has been described in detail through reference to preferred embodiments, the present application is not limited to such preferred embodiments. Without departing from the spirit and essential characteristics of the present application, various equivalent modifications and substitutions can be made by those skilled in the art. Such modifications and substitutions should be included in the scope of the present application. Any skilled person in the art can easily think of changes or substitutions within the technical range disclosed by the present application, which should be included in the protection scope of the present application.

Claims

1. A torsional vibration prediction method for grid-forming direct-drive wind turbines, characterized in that, The method comprises the following steps: constructing a small signal model of the grid-connected direct-driven wind turbine; deducing the relationship between the port voltage and current signals of the grid-connected direct-driven wind turbine and the shaft torsional vibration of the grid-connected direct-driven wind turbine when forced oscillation occurs based on a shaft double-mass block model, wherein the double-mass block comprises a generator mass block and a turbine mass block; specifically, the state matrix generated by normalizing the shaft state space equation based on the shaft double-mass block model is made 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-connected direct-driven wind turbine and the shaft torsional vibration of the grid-connected direct-driven wind turbine is obtained; 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-connected direct-driven wind turbine; the calculated voltage and current signals are taken as the input of the small signal model of the grid-connected direct-driven wind turbine, and the shaft torsional vibration of the grid-connected direct-driven wind turbine caused by forced oscillation is calculated based on the relationship between the port voltage and current signals of the grid-connected direct-driven wind turbine and the shaft torsional vibration of the grid-connected direct-driven wind turbine; specifically, when forced oscillation occurs, the voltage and current signals of the grid node port equipped with a PMU measuring device are measured; the transfer function between different grid node ports is obtained by constructing the s-domain node admittance matrix of the wind farm, and based on the measured voltage and current signals, the voltage and current signals of the grid-connected direct-driven wind turbine port are calculated; the calculated voltage and current signals are taken as the input of the small signal model of the grid-connected direct-driven wind turbine, and the electromagnetic power small signal of the grid-connected direct-driven wind turbine port is calculated; the transfer function relationship between the electromagnetic power small signal of the grid-connected direct-driven wind turbine port and the electromagnetic torque small signal of the synchronous generator and the mechanical speed small signal of the synchronous generator rotor is constructed, and the electromagnetic torque of the synchronous generator is calculated based on the electromagnetic power of the grid-connected direct-driven wind turbine port; 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 size of the shaft torsional vibration of the grid-connected direct-driven wind turbine is calculated according to the electromagnetic torque of the synchronous generator and the mechanical torque of the wind turbine and the mapping relationship between the actual torque angle mode and the decoupled torque angle mode.

2. The torsional vibration prediction method for a grid-connected direct drive wind turbine according to claim 1, characterized in that, The step of constructing the small signal model of the grid-connected direct-driven wind turbine comprises: constructing a grid-side converter small signal model of the grid-connected direct-driven wind turbine; constructing a machine-side small signal model of the grid-connected direct-driven wind turbine; combining the grid-side converter small signal model of the grid-connected direct-driven wind turbine and the machine-side small signal model of the grid-connected direct-driven wind turbine in series to form a complete small signal model of the grid-connected direct-driven wind turbine.

3. The torsional vibration prediction method for a grid-connected direct drive wind turbine according to claim 2, characterized in that The step of constructing the grid-side converter small signal model of the grid-connected direct-driven wind turbine comprises: The state equation of the power ring is constructed, specifically including: constructing the state equation of the first-order low-pass link and performing linearization processing; constructing the state equation of the active power link and performing linearization processing; constructing the state equation of the reactive power link and performing linearization processing; The state equation of the voltage and current double closed loop is constructed and linearized; The state equation of the filter circuit is constructed and linearized; The state equations of the constructed power ring, voltage and current double closed loop and filter circuit are integrated; The integrated state equation is converted into a small signal equation to obtain a small signal model of the grid-side converter of the grid-connected direct-driven wind turbine.

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

5. The torsional vibration prediction method for a grid-connected direct drive wind turbine according to claim 4, characterized in that, The steps of normalizing the shaft system state space equation based on the shaft system double mass block model to generate a state matrix and making the state matrix into a diagonal matrix to extract the gain, damping coefficient and oscillation frequency of each mode include: The shaft system state space equation based on the shaft system double mass block model is normalized to generate a state matrix; The normalized state matrix is diagonalized to extract left and right eigenvectors and obtain a decoupled matrix; The gain, damping coefficient and oscillation frequency of each mode are calculated based on the decoupled matrix.

6. A networked direct drive wind turbine torsional vibration prediction device for implementing the method of any one of claims 1-5, characterized by, The model construction module, the torsional vibration modal analysis module and the shaft system torsional vibration estimation module are included; The model construction module is used to construct a small signal model of the grid-connected direct-driven wind turbine; The torsional vibration modal analysis module is used to deduce the relationship between the grid-connected direct-driven wind turbine port voltage and current signals and the grid-connected direct-driven wind turbine shaft system torsional vibration when forced oscillation occurs based on the shaft system double mass block model, wherein the double mass block includes a generator mass block and a turbine mass block; The shaft torsional vibration estimation module is configured to, when forced oscillation occurs, obtain the transfer function between different power grid node ports by constructing a wind farm s-domain node admittance model, so as to calculate the required power grid node port voltage and current signals, i.e., the grid-connected direct-drive wind turbine port voltage and current signals, take the calculated voltage and current signals as the input of the small-signal model of the grid-connected direct-drive wind turbine, and calculate the grid-connected direct-drive wind turbine shaft torsional vibration caused by the forced oscillation in combination with the relationship between the grid-connected direct-drive wind turbine port voltage and current signals and the grid-connected direct-drive wind turbine shaft torsional vibration.

7. An electronic device, comprising: The electronic device includes at least one processor, and a memory connected with the at least one processor in communication; 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 to enable the at least one processor to perform the grid-connected direct-drive wind turbine torsional vibration prediction method according to any one of claims 1 to 5.

8. A non-transitory computer-readable storage medium, comprising: The non-transitory computer readable storage medium stores computer instructions, and the computer instructions enable the computer to perform the grid-connected direct-drive wind turbine torsional vibration prediction method according to any one of claims 1 to 5.

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