Subsynchronous oscillation suppression method and suppression system for offshore wind turbine generator

Abstract

The invention discloses a subsynchronous oscillation suppression method and suppression system for an offshore wind turbine generator, and relates to the technical field of new energy grid-connected control, and the method comprises the steps: obtaining a stator current signal and an actual rotating speed of the wind turbine generator, and carrying out the preprocessing of the stator current signal; constructing a three-order expansion state observer model based on the preprocessed stator current signal, determining an observer gain parameter through simulation optimization, and extracting a disturbance component; calculating an error signal according to a difference value between the preprocessed stator current signal and a first-order state variable output by a third-order expansion state observer model, generating a dynamic compensation signal based on the error signal and a disturbance component in combination with a nonlinear feedback mechanism, and superposing the dynamic compensation signal to an original current instruction to form a corrected current instruction; according to the amplitude of the disturbance component, the resistance, inductance and capacitance of the virtual impedance are dynamically adjusted according to the disturbance amplitude, and a virtual impedance control signal is obtained; and superposing the corrected current instruction and the virtual impedance control signal to generate a final current instruction.

Description

Technical Field

[0001] This invention relates to the field of new energy grid connection control technology, and in particular to a method and system for suppressing subsynchronous oscillations in offshore wind turbines. Background Technology

[0002] With the continuous increase in the penetration rate of offshore wind power, the subsynchronous oscillation problem in wind turbine grid-connected systems is becoming increasingly prominent, becoming a key challenge restricting grid stability. In existing technologies, active disturbance rejection control (ADRC) estimates disturbances by extending the state observer and combining it with a nonlinear feedback strategy, achieving certain results in suppressing subsynchronous current disturbances on the rotor side of doubly-fed induction generators. The virtual impedance method enhances system damping by adjusting the converter impedance parameters. Meanwhile, band-stop filters suppress oscillations by matching specific oscillation frequencies with frequency domain characteristics. However, ADRC and the virtual impedance method mostly rely on fixed parameters or a single control strategy, which has limitations in dynamic response, multi-source disturbance coupling, and parameter uncertainty scenarios.

[0003] Existing technologies still have room for improvement in terms of disturbance estimation accuracy and dynamic compensation flexibility. For example, active disturbance rejection control is sensitive to high-frequency noise and relies on model simplification. The virtual impedance method is difficult to achieve real-time correlation between parameters and disturbance amplitude, while the frequency adaptability of band-stop filters is limited to a preset range. This invention extracts disturbance components by constructing a third-order extended state observer and combines it with dynamic adjustment of virtual impedance and saturation function compensation. This can adapt to the subsynchronous oscillation characteristics under complex operating conditions and improve robustness and real-time suppression efficiency. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a method for suppressing subsynchronous oscillations in offshore wind turbines to solve the problem that the frequency adaptability of band-stop filters is limited to a preset range.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for suppressing subsynchronous oscillations in offshore wind turbines, comprising:

[0008] The stator current signal and actual speed of the wind turbine are acquired in real time, and the stator current signal is denoised using a low-pass filter.

[0009] A third-order extended state observer model is constructed based on the preprocessed stator current signal. The observer gain parameters are determined through simulation optimization. The third-order state variable output by the third-order extended state observer model is used to extract the disturbance component of the subsynchronous oscillation and reflect the abnormal fluctuations in the current.

[0010] The error signal is calculated based on the difference between the preprocessed stator current signal and the first-order state variable output by the third-order extended state observer model. Based on the error signal and the disturbance component, a dynamic compensation signal is generated by combining the nonlinear feedback mechanism and superimposed on the original current command to form the corrected current command.

[0011] Based on the magnitude of the disturbance component, the intensity of the current synchronous oscillation is quantified, and the resistance, inductance, and capacitance of the virtual impedance are dynamically adjusted according to the disturbance amplitude to obtain the virtual impedance control signal.

[0012] The corrected current command is superimposed with the virtual impedance control signal to generate the final current command. The final current command is then limited and input to the converter PI controller to generate the voltage command.

[0013] As a preferred embodiment of the subsynchronous oscillation suppression method for offshore wind turbines described in this invention, the step of performing noise reduction processing on the stator current signal using a low-pass filter specifically involves:

[0014] The cutoff frequency of the low-pass filter is set according to the typical frequency range of the electrical quantities of the wind turbine. The typical frequency range is determined based on power quality measurements. The low-pass filter achieves noise reduction by suppressing noise components above the cutoff frequency, retaining the fundamental component of the stator current signal and suppressing high-frequency disturbance components.

[0015] As a preferred embodiment of the subsynchronous oscillation suppression method for offshore wind turbines described in this invention, the specific steps of constructing a third-order extended state observer model based on the preprocessed stator current signal include:

[0016] Bandwidth is set using the pole placement method. The gain parameters are calculated based on the bandwidth, and the gain parameters satisfy:

[0017] ;

[0018] in, , and For the gain parameters of the third-order extended state observer model;

[0019] The state update equation is numerically integrated using the Euler method, and the output disturbance estimate is calculated iteratively.

[0020] As a preferred embodiment of the subsynchronous oscillation suppression method for offshore wind turbines described in this invention, the step of generating a dynamic compensation signal by combining a nonlinear feedback mechanism specifically includes:

[0021] The difference between the preprocessed stator current signal and the first-order state variable of the observer is used as the error signal. Combined with the disturbance estimate, the signal is input into the saturation function to generate a dynamic compensation signal. The amplitude of the dynamic compensation signal is limited by setting a saturation threshold.

[0022] As a preferred embodiment of the subsynchronous oscillation suppression method for offshore wind turbines described in this invention, the specific steps of dynamically adjusting the resistance, inductance, and capacitance of the virtual impedance include:

[0023] Based on the root mean square value of the disturbance amplitude, the virtual impedance parameters are generated by superimposing or subtracting the products of the disturbance amplitude with the damping enhancement coefficient, the virtual inductance gain coefficient, and the virtual capacitance gain coefficient to the virtual resistance reference value, the virtual inductance reference value, and the virtual capacitance reference value, respectively.

[0024] As a preferred embodiment of the method for suppressing subsynchronous oscillations of offshore wind turbines described in this invention, the method of limiting the final current command means that if the active and reactive components in the final current command exceed the upper limit of the rated current of the converter, the active and reactive components in the final current command are clamped to the upper limit.

[0025] If the active and reactive components in the final current command are lower than the lower limit of the rated current, then the active and reactive components in the final current command will be clamped to the lower limit.

[0026] As a preferred embodiment of the subsynchronous oscillation suppression method for offshore wind turbines described in this invention, the generation of voltage commands specifically includes:

[0027] Based on the error signal between the current command after limiting and the actual current, the voltage command is calculated by the converter proportional-integral controller, and then the three-phase AC voltage is output by the converter switching devices through the pulse width modulator, forming a closed-loop control circuit to dynamically suppress subsynchronous oscillation.

[0028] Secondly, the present invention provides a subsynchronous oscillation suppression system for offshore wind turbines, comprising:

[0029] The signal preprocessing module is used to acquire the stator current signal and actual speed signal of the wind turbine in real time. It performs noise reduction processing on the stator current signal through a low-pass filter to suppress high-frequency noise and retain the fundamental component.

[0030] The disturbance detection module is used to construct a third-order extended state observer model based on the preprocessed stator current signal, set the observer gain parameter by the pole placement method, iteratively calculate the disturbance estimate using the Euler method, and output the disturbance component to quantify the subsynchronous oscillation intensity.

[0031] The dynamic compensation module is used to calculate the error signal based on the difference between the preprocessed current signal and the first-order state variable of the observer. Combining the error signal and the disturbance estimate, a dynamic compensation signal is generated through a nonlinear feedback mechanism. The compensation signal is then superimposed on the original current command to generate a corrected current command.

[0032] The virtual impedance adjustment module quantifies the subsynchronous oscillation intensity based on the root mean square value of the disturbance estimate, dynamically adjusts the virtual resistance, inductance, and capacitance, and generates a virtual impedance control signal by combining the adjusted parameters.

[0033] The closed-loop control module is used to superimpose the corrected current command with the virtual impedance control signal to generate the final current command, perform amplitude limiting on the final current command, input the amplitude-limited final current command into the converter PI controller to generate a voltage command, generate a pulse width modulation signal through the PWM modulator, drive the converter to output three-phase AC voltage, and form a closed-loop control loop to suppress subsynchronous oscillation.

[0034] Thirdly, the present invention provides a computer device including a memory and a processor, wherein the memory stores a computer program, wherein when the computer program is executed by the processor, it implements any step of the method for suppressing subsynchronous oscillations of offshore wind turbines as described in the first aspect of the present invention.

[0035] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements any step of the method for suppressing subsynchronous oscillations of offshore wind turbines as described in the first aspect of the present invention.

[0036] The beneficial effects of this invention are as follows: By preprocessing the stator current signal with low-pass filtering, this invention achieves high-frequency noise suppression and preservation of the fundamental component, providing a high signal-to-noise ratio data foundation for subsequent disturbance extraction; by constructing a third-order extended state observer and optimizing the gain parameters using the pole placement method, it achieves accurate dynamic estimation of the subsynchronous disturbance component, enhancing sensitivity to weak abnormal fluctuations; by generating a dynamic compensation signal through a nonlinear feedback mechanism, it achieves synergistic suppression of errors and disturbances, improving control response speed and stability; by dynamically adjusting the virtual impedance driven by the disturbance amplitude, it achieves adaptive matching of damping characteristics and oscillation intensity, enhancing robustness; and by using amplitude limiting processing and closed-loop control circuit design, it achieves safe operation of the converter and continuous suppression of subsynchronous oscillations, ultimately improving the stability of the wind turbine unit. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of a method for suppressing subsynchronous oscillations in offshore wind turbines.

[0039] Figure 2 This is a schematic diagram of a third-order extended state observer model.

[0040] Figure 3 The logic diagram for generating dynamic compensation signals.

[0041] Figure 4 This is a flowchart for dynamic adjustment of virtual impedance. Detailed Implementation

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0045] Reference Figures 1 to 4 This is one embodiment of the present invention, which provides a method for suppressing subsynchronous oscillations of offshore wind turbines, comprising the following steps:

[0046] S1. Real-time acquisition of stator current signal and actual speed of wind turbine, and noise reduction processing of stator current signal through low-pass filter;

[0047] The stator current signal is acquired in real time by a current sensor installed on the stator side of the wind turbine, and the actual speed is obtained by monitoring the generator speed in real time by a speed sensor.

[0048] The acquired stator current signal is input into a low-pass filter. The cutoff frequency of the low-pass filter is set. The cutoff frequency of the low-pass filter (50Hz or 60Hz + 5%~10%) is set according to the typical frequency range of the electrical quantities of the wind turbine. The typical frequency range is set according to the power quality measurement method. The filter suppresses noise components above the cutoff frequency according to the set cutoff frequency. The noise components include electromagnetic interference and measurement noise.

[0049] The low-pass filter outputs a noise-reduced stator current signal, which retains the fundamental component while suppressing high-frequency disturbance components.

[0050] S2. Based on the preprocessed stator current signal, a third-order extended state observer model is constructed. The observer gain parameters are determined through simulation optimization. The third-order state variable output by the third-order extended state observer model is used to extract the disturbance component of the subsynchronous oscillation to reflect the abnormal fluctuations in the current.

[0051] The first-order state variable of the third-order extended state observer model is set as the actual current, the second-order state variable is the rate of change of current, and the third-order state variable is the disturbance estimate. A state update equation is constructed based on these three state variables, expressed as:

[0052] ;

[0053] in, This represents the actual current, i.e., the pre-processed stator current signal. The first-order state variable output by the third-order extended state observer model represents the current estimate by the third-order extended state observer model. The second-order state variable output by the third-order extended state observer model represents the estimate of the rate of change of current by the third-order extended state observer model. The third-order state variable is the output of the third-order extended state observer model, representing the model's estimate of the disturbance. , and These are the gain parameters for the third-order extended state observer model. This represents the disturbance estimate, which is obtained iteratively from the state update equation and is a third-order state variable. Part of it, reflecting real-time estimates of disturbances;

[0054] The gain parameter is set using the pole placement method to calculate the bandwidth, with the bandwidth set as follows: ;

[0055] ;

[0056] The state update equation is numerically integrated using the Euler method, and the update formula for the state variables is as follows:

[0057] ;

[0058] in, Indicates a time interval.

[0059] S3. Calculate the error signal based on the difference between the preprocessed stator current signal and the first-order state variable output by the third-order extended state observer model. Based on the error signal and disturbance components, generate a dynamic compensation signal by combining a nonlinear feedback mechanism, and superimpose it onto the original current command to form a corrected current command.

[0060] The difference between the preprocessed stator current signal and the first-order state variable output by the third-order extended state observer model is used as the error signal. ;

[0061] Error signal The third-order state variable (i.e., the disturbance estimate) output by the third-order extended state observer model is used as the input to the nonlinear feedback mechanism. The input expression for the nonlinear feedback mechanism is:

[0062] ;

[0063] in, This represents the weighted combination of the error signal and the disturbance estimate. and For nonlinear feedback gain coefficients;

[0064] Through nonlinear functions Processing is performed to generate dynamic compensation signals. Treating the saturation function as a nonlinear function, its expression is:

[0065] ;

[0066] in, This represents the saturation threshold, used to limit the amplitude of the dynamic compensation signal and prevent excessive disturbances from affecting system stability. This represents the saturation function.

[0067] Dynamic compensation signal The modified current command is generated by superimposing it on the original current command.

[0068] The raw current command includes active power command and reactive power command. The active power command refers to the target active power calculated by the maximum power point tracking (MPPT) algorithm based on real-time data from wind speed sensors and generator speed sensors, and then converted into an active power command according to the grid voltage and power formula. The reactive power command refers to the reactive power reference value issued by the grid dispatch center, which is also converted into a reactive power command through the power formula.

[0069] S4. Based on the magnitude of the disturbance component, quantify the intensity of the current synchronous oscillation, and dynamically adjust the resistance, inductance, and capacitance of the virtual impedance according to the disturbance amplitude to obtain the virtual impedance control signal.

[0070] The third-order state variable (i.e., the disturbance estimate) output by the third-order extended state observer model is used as input. The disturbance amplitude is obtained by calculating its root mean square value. The root mean square value is calculated by averaging the square values ​​of the disturbance estimate within a specific time window and then taking the square root.

[0071] Based on the initial operating state of the wind turbine, a reference value for the virtual impedance is set. This reference value includes a reference value for virtual resistance, a reference value for virtual inductance, and a reference value for virtual capacitance. The specific steps for determining the reference value for virtual resistance are as follows:

[0072] Based on the switching frequency of the converter, the power loss under different load conditions is calculated. This power loss can be converted into equivalent resistance. Combined with the resistance values ​​of the cables and transformers connecting the generator to the grid connection point, the resistance values ​​are converted into equivalent resistance. 10% to 20% of the total equivalent resistance is selected as the virtual resistance reference value.

[0073] The specific steps for determining the virtual inductance reference value are as follows: using known grid parameters, measure the grid impedance seen from the wind farm connection point; based on the grid parameters, calculate the total inductive component, which is the sum of line inductance and transformer leakage inductance; using the impedance matching principle, convert the inductive component into an equivalent inductance relative to the wind farm output; and adjust the equivalent inductance value according to the required damping enhancement coefficient so that the equivalent inductance value can both ensure stability and effectively suppress subsynchronous oscillations.

[0074] The specific steps for determining the virtual capacitor reference value are as follows: Analyze the voltage and current signals at the wind farm connection point using the Fast Fourier Transform (FFT) spectrum analysis tool to identify the resonant frequency and find the frequency point where resonance occurs. For each resonant frequency, calculate the required compensation capacitor value based on the capacitance and frequency. Based on actual needs and capacity limitations, select a capacitor value that does not exceed the maximum allowable capacitance value of the converter and has an impact of less than 5% on the reactive power of the power grid as the virtual capacitor reference value to ensure that resonance is effectively suppressed without causing new instability factors.

[0075] The disturbance amplitude is multiplied by the damping enhancement coefficient and then added to the virtual resistance reference value to generate the adjusted virtual resistance value. If the disturbance amplitude is large, the virtual resistance value is increased proportionally based on the reference value to enhance the damping effect on the subsynchronous oscillation.

[0076] The disturbance amplitude is multiplied by the preset virtual inductance gain coefficient and then added to the virtual inductance reference value to generate the adjusted virtual inductance value. If the disturbance amplitude is large, the virtual inductance value is increased proportionally based on the reference value to suppress the current loop gain of the subsynchronous oscillation.

[0077] Multiply the disturbance amplitude by the preset virtual capacitance gain coefficient, and subtract the product from the virtual capacitance reference value to generate the adjusted virtual capacitance value. If the disturbance amplitude is large, the virtual capacitance value is reduced proportionally from the reference value to reduce the resonance risk in the sub-synchronization frequency band. The expression is as follows:

[0078] Adjusted virtual resistance value = Virtual resistance reference value + (Disturbance amplitude × Damping enhancement coefficient);

[0079] Adjusted virtual inductance value = Virtual inductance reference value + (Disturbance amplitude × Virtual inductance gain coefficient);

[0080] Adjusted virtual capacitance value = Virtual capacitance reference value - (Perturbation amplitude × Virtual capacitance gain coefficient);

[0081] The adjusted virtual resistance, virtual inductance, and virtual capacitance values ​​are combined into a virtual impedance control signal, which contains the three adjusted parameters.

[0082] S5. The corrected current command is superimposed with the virtual impedance control signal to generate the final current command. The final current command is then limited. The limited final current command is input into the converter PI controller to generate the voltage command.

[0083] The corrected current command and the virtual impedance control signal are superimposed point by point in the current control loop to generate the final current command. The corrected current command includes active power command and reactive power command. The value of the corrected current command has been adjusted by the dynamic compensation signal. The virtual impedance control signal contains the adjusted virtual resistance value, virtual inductance value and virtual capacitance value. The value of the virtual impedance control signal has been dynamically adjusted according to the disturbance amplitude. The three parameters in the virtual impedance control signal are added to the corresponding components in the corrected current command to generate the active component and reactive component of the final current command.

[0084] The final current command is limited based on the upper and lower limits of the converter's rated current, specifically as follows:

[0085] If the active or reactive component in the final current command exceeds the rated current limit, the active or reactive component in the final current command will be clamped to the rated current limit. If any component in the final current command is lower than the rated current limit, the active or reactive component in the final current command will be clamped to the rated current limit to ensure that the current output by the converter does not exceed the range allowed by its hardware and avoid equipment damage due to overload.

[0086] The limited active power command and reactive power command are used as input signals and sent to the proportional-integral controller of the converter. According to the adjustment rules of the proportional-integral controller, the corresponding voltage command is calculated, including active voltage component and reactive voltage component. Specifically, the proportional-integral controller performs integral and proportional calculations based on the error signal (the difference between the limited current command and the actual current) to generate the voltage command. The voltage command is used to drive the switching devices (such as IGBTs) of the converter and adjust the output voltage to match the current command requirements.

[0087] The voltage command output by the converter's proportional-integral controller is applied to the converter's PWM modulator to generate a pulse width modulation signal to control the converter's switching state. The pulse width modulation signal drives the converter to output a three-phase AC voltage that conforms to the voltage command. The three-phase AC voltage is connected to the grid through a grid-connected inverter to form a closed-loop control circuit, dynamically adjusting the current to suppress subsynchronous oscillations.

[0088] This embodiment also provides a subsynchronous oscillation suppression system for offshore wind turbines, including:

[0089] The signal preprocessing module is used to acquire the stator current signal and actual speed signal of the wind turbine in real time. It performs noise reduction processing on the stator current signal through a low-pass filter to suppress high-frequency noise and retain the fundamental component.

[0090] The disturbance detection module is used to construct a third-order extended state observer model based on the preprocessed stator current signal, set the observer gain parameter by the pole placement method, iteratively calculate the disturbance estimate using the Euler method, and output the disturbance component to quantify the subsynchronous oscillation intensity.

[0091] The dynamic compensation module is used to calculate the error signal based on the difference between the preprocessed current signal and the first-order state variable of the observer. Combining the error signal and the disturbance estimate, a dynamic compensation signal is generated through a nonlinear feedback mechanism. The compensation signal is then superimposed on the original current command to generate a corrected current command.

[0092] The virtual impedance adjustment module quantifies the subsynchronous oscillation intensity based on the root mean square value of the disturbance estimate, dynamically adjusts the virtual resistance, inductance, and capacitance, and generates a virtual impedance control signal by combining the adjusted parameters.

[0093] The closed-loop control module is used to superimpose the corrected current command with the virtual impedance control signal to generate the final current command, perform amplitude limiting on the final current command, input the amplitude-limited final current command into the converter PI controller to generate a voltage command, generate a pulse width modulation signal through the PWM modulator, drive the converter to output three-phase AC voltage, and form a closed-loop control loop to suppress subsynchronous oscillation.

[0094] This embodiment also provides a computer device applicable to the method for suppressing subsynchronous oscillations of offshore wind turbines, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the method for suppressing subsynchronous oscillations of offshore wind turbines as proposed in the above embodiment.

[0095] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0096] This embodiment also provides a storage medium storing a computer program, which, when executed by a processor, implements the method for suppressing subsynchronous oscillations of offshore wind turbines as proposed in the above embodiments. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0097] In summary, this invention achieves high-frequency noise suppression and fundamental component retention by: preprocessing the stator current signal with low-pass filtering, providing a high signal-to-noise ratio data foundation for subsequent disturbance extraction; accurately and dynamically estimating subsynchronous disturbance components by constructing a third-order extended state observer and optimizing gain parameters using the pole placement method, enhancing sensitivity to weak abnormal fluctuations; generating dynamic compensation signals through a nonlinear feedback mechanism, achieving synergistic suppression of errors and disturbances, improving control response speed and stability; dynamically adjusting the virtual impedance driven by disturbance amplitude, achieving adaptive matching of damping characteristics and oscillation intensity, enhancing robustness; and achieving safe converter operation and continuous suppression of subsynchronous oscillations through amplitude limiting and closed-loop control design, ultimately improving the stability of the wind turbine.

[0098] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for suppressing subsynchronous oscillations in offshore wind turbines, characterized in that: include: The stator current signal and actual speed of the wind turbine are acquired in real time, and the stator current signal is denoised using a low-pass filter. A third-order extended state observer model is constructed based on the preprocessed stator current signal. The observer gain parameters are determined through simulation optimization. The third-order state variable output by the third-order extended state observer model is used to extract the disturbance component of the subsynchronous oscillation and reflect the abnormal fluctuations in the current. The error signal is calculated based on the difference between the preprocessed stator current signal and the first-order state variable output by the third-order extended state observer model. Based on the error signal and the disturbance component, a dynamic compensation signal is generated by combining the nonlinear feedback mechanism and superimposed on the original current command to form the corrected current command. Based on the magnitude of the disturbance component, the intensity of the current synchronous oscillation is quantified, and the resistance, inductance, and capacitance of the virtual impedance are dynamically adjusted according to the disturbance amplitude to obtain the virtual impedance control signal. The corrected current command is superimposed with the virtual impedance control signal to generate the final current command. The final current command is then limited and input to the converter PI controller to generate the voltage command.

2. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 1, characterized in that: The noise reduction processing of the stator current signal using a low-pass filter is specifically as follows: The cutoff frequency of the low-pass filter is set according to the typical frequency range of the electrical quantities of the wind turbine. The typical frequency range is determined based on power quality measurements. The low-pass filter achieves noise reduction by suppressing noise components above the cutoff frequency, retaining the fundamental component of the stator current signal and suppressing high-frequency disturbance components.

3. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 2, characterized in that: The specific steps for constructing a third-order extended state observer model based on the preprocessed stator current signal include: Bandwidth is set using the pole placement method. The gain parameters are calculated based on the bandwidth, and the gain parameters satisfy: ； in, , and For the gain parameters of the third-order extended state observer model; The state update equation is numerically integrated using the Euler method, and the output disturbance estimate is calculated iteratively.

4. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 3, characterized in that: The specific steps for generating the dynamic compensation signal using the nonlinear feedback mechanism include: The difference between the preprocessed stator current signal and the first-order state variable of the observer is used as the error signal. Combined with the disturbance estimate, the signal is input into the saturation function to generate a dynamic compensation signal. The amplitude of the dynamic compensation signal is limited by setting a saturation threshold.

5. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 4, characterized in that: The specific steps for dynamically adjusting the resistance, inductance, and capacitance of the virtual impedance include: Based on the root mean square value of the disturbance amplitude, the virtual impedance parameters are generated by superimposing or subtracting the products of the disturbance amplitude with the damping enhancement coefficient, the virtual inductance gain coefficient, and the virtual capacitance gain coefficient to the virtual resistance reference value, the virtual inductance reference value, and the virtual capacitance reference value, respectively.

6. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 5, characterized in that: The aforementioned limiting processing of the final current command refers to clamping the active and reactive components in the final current command to the upper limit of the rated current if the active and reactive components in the final current command exceed the upper limit of the rated current, based on the upper and lower limits of the converter's rated current. If the active and reactive components in the final current command are lower than the lower limit of the rated current, then the active and reactive components in the final current command will be clamped to the lower limit.

7. The method for suppressing subsynchronous oscillations of offshore wind turbines as described in claim 6, characterized in that: The voltage generation command is specifically as follows: Based on the error signal between the current command after limiting and the actual current, the voltage command is calculated by the converter proportional-integral controller, and then the three-phase AC voltage is output by the converter switching devices through the pulse width modulator, forming a closed-loop control circuit to dynamically suppress subsynchronous oscillation.

8. A subsynchronous oscillation suppression system for offshore wind turbines, based on the subsynchronous oscillation suppression method for offshore wind turbines according to any one of claims 1 to 7, characterized in that: include: The signal preprocessing module is used to acquire the stator current signal and actual speed signal of the wind turbine in real time. It performs noise reduction processing on the stator current signal through a low-pass filter to suppress high-frequency noise and retain the fundamental component. The disturbance detection module is used to construct a third-order extended state observer model based on the preprocessed stator current signal, set the observer gain parameter by the pole placement method, iteratively calculate the disturbance estimate using the Euler method, and output the disturbance component to quantify the subsynchronous oscillation intensity. The dynamic compensation module is used to calculate the error signal based on the difference between the preprocessed current signal and the first-order state variable of the observer. Combining the error signal and the disturbance estimate, a dynamic compensation signal is generated through a nonlinear feedback mechanism. The compensation signal is then superimposed on the original current command to generate a corrected current command. The virtual impedance adjustment module quantifies the subsynchronous oscillation intensity based on the root mean square value of the disturbance estimate, dynamically adjusts the virtual resistance, inductance, and capacitance, and generates a virtual impedance control signal by combining the adjusted parameters. The closed-loop control module is used to superimpose the corrected current command with the virtual impedance control signal to generate the final current command, perform amplitude limiting on the final current command, input the amplitude-limited final current command into the converter PI controller to generate a voltage command, generate a pulse width modulation signal through the PWM modulator, drive the converter to output three-phase AC voltage, and form a closed-loop control loop to suppress subsynchronous oscillation.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the method for suppressing subsynchronous oscillations of offshore wind turbines as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the method for suppressing subsynchronous oscillations of offshore wind turbines as described in any one of claims 1 to 7.

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