A method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system

Abstract

This invention discloses a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system, relating to the field of power system stability control technology. The specific steps of the method are as follows: S100 extracting the amplitude and phase angle of the subsynchronous frequency component; S200 generating a rotor compensation current command from the amplitude, phase angle, and dynamic gain of the subsynchronous component; S300 dynamically adjusting the gain during operation based on the suppression rate and the target magnetic field amplitude; S400 calculating the feedforward decoupling voltage; S500 calculating the suppression rate after injection and executing a hierarchical control strategy. This invention achieves subsynchronous oscillation suppression at the electromagnetic level. By real-time monitoring of the subsynchronous component of the air gap magnetic field and injecting a reverse-phase compensation current on the rotor side, the stator and rotor magnetic fields actively interfere and cancel each other in the subsynchronous frequency band, directly blocking the energy transfer path of the subsynchronous oscillation and destroying the oscillation formation conditions. The dynamic gain adjustment mechanism optimizes the compensation intensity based on the real-time suppression effect to cope with the frequency variation of the 5-45Hz subsynchronous oscillation.

Description

Technical Field

[0001] This invention relates to the field of power system stability control technology, specifically a method for suppressing subsynchronous oscillations in a doubly fed grid system. Background Technology

[0002] Doubly fed induction generators (DFIGs) have become the mainstream model in the wind power generation field due to their efficient variable speed constant frequency operation capability. However, in doubly fed grid-connected systems, the problem of subsynchronous oscillation has become increasingly prominent due to the widespread use of series compensation capacitors to improve transmission capacity and system stability, as well as the impedance characteristic changes caused by the increasingly complex grid structure. Subsynchronous oscillation can cause torsional vibration of the generator shaft and violent fluctuations in electrical quantities. In severe cases, it can even lead to major accidents such as shaft breakage, equipment damage, and grid disconnection. Therefore, effectively suppressing the subsynchronous oscillation of doubly fed grid-connected systems has become a key technical challenge to ensure the safe and stable operation of the power system.

[0003] In existing technologies, methods for suppressing DFIG subsynchronous oscillations are mainly divided into two categories: passive suppression (such as adding damping filters) and active control (such as adding damping control to the converter). However, passive suppression schemes have significant drawbacks: damping filters need to be designed for specific oscillation frequencies, and when the grid operating conditions change, the filter parameters become mismatched, leading to a decrease in suppression effect. The addition of hardware increases system cost and size, and it is not compatible with wind turbines already in operation. Although active control schemes achieve dynamic suppression by injecting compensation current into the converter, existing technologies use PI controllers with fixed parameters, which have limited response speed and anti-interference capabilities. Especially in scenarios where multimodal oscillations coexist, the compensation current is prone to phase lag or amplitude overshoot, requiring manual intervention to adjust control parameters, which is difficult to meet the unattended operation and maintenance requirements of wind farms.

[0004] In summary, existing subsynchronous oscillation suppression technologies suffer from poor adaptability and insufficient control precision, making it difficult to effectively cope with complex and ever-changing power grid operating conditions. Therefore, there is an urgent need for a new method that can actively suppress subsynchronous oscillations from an electromagnetic perspective, while also possessing adaptive adjustment capabilities and high reliability, in order to improve the stability and security of doubly-fed grid-connected systems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for suppressing subsynchronous oscillations in doubly-fed grid-connected systems. This method achieves subsynchronous oscillation suppression at the electromagnetic level by real-time monitoring of the subsynchronous component of the air gap magnetic field and injecting a reverse-phase compensation current on the rotor side. This causes the stator and rotor magnetic fields to actively interfere and cancel each other out in the subsynchronous frequency band, directly blocking the energy transfer path of the subsynchronous oscillation and disrupting the conditions for oscillation formation. The dynamic gain adjustment mechanism optimizes the compensation intensity based on the real-time suppression effect. The triple decision logic combined with the high-frequency auxiliary signal strategy can cope with the frequency variation of subsynchronous oscillations from 5-45Hz, avoiding the problem of insufficient adaptability of fixed parameter control to frequency drift and improving the universality and effectiveness of the suppression strategy.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system, the specific steps of which are as follows:

[0007] S100. Air Gap Magnetic Field Monitoring and Feature Extraction: Based on the air gap magnetic field anomalies caused by the subsynchronous oscillation during doubly-fed wind turbine operation, a three-axis Hall sensor array is used to collect the air gap magnetic field signal in real time. The collected signal is then bandpass filtered to remove interference from other frequency bands, and spectrum analysis is performed to extract the amplitude of the subsynchronous frequency component. and phase angle And perform signal redundancy verification and anomaly handling;

[0008] S200, Rotor compensation current command generation: based on the amplitude of the subsynchronous frequency component. and phase angle and the dynamic gain coefficient provided by S300 Based on the mutual inductance characteristics of the stator and rotor of the doubly fed wind turbine, a compensation current function is established and a rotor compensation current command is generated based on the magnetomotive force balance. ;

[0009] S300, Dynamic Gain Adjustment: During initial system startup, the gain is adjusted... Set as It provides compensation current during system startup and in the event of sudden oscillations, quickly responding to the need for suppressing subsynchronous oscillations. During system operation, it adjusts the suppression rate based on feedback from the S500. And the set target magnetic field amplitude, affecting the gain Dynamically adjust to generate new gain coefficients and will The instruction is passed to S200 for the generation of the next control cycle;

[0010] S400, Current Injection and Feedforward Decoupling: Decoupling the Compensation Current Command The signal is converted into a control signal and injected into the system. It is then superimposed on the reference value of the rotor-side converter current loop to calculate the feedforward decoupling voltage to eliminate dq-axis current coupling and compensate for subsynchronous oscillation.

[0011] S500, Suppression Verification and Strategy Switching: 200ms after the compensation current injection, the amplitude of the subsynchronous frequency component of the air gap magnetic field is measured again using a triaxial Hall sensor array, and the suppression rate is calculated. A hierarchical control strategy is executed based on the inhibition rate.

[0012] Furthermore, in the S100 air gap magnetic field monitoring and feature extraction, a triaxial Hall sensor array is arranged along the circumferential direction of the air gap between the stator and rotor of the doubly-fed induction generator (DFIG). Each sensor group contains three mutually perpendicular Hall elements (X, Y, and Z) used to synchronously acquire the vector components of the air gap magnetic field in three-dimensional space. The sampling frequency of the triaxial Hall sensor array is set to 20kHz. The acquired raw magnetic field signal is input to a bandpass filter. Through filtering, power frequency and its harmonic interference, as well as high-frequency mechanical vibration noise, are effectively filtered out, and a clean subsynchronous frequency band magnetic field signal is output. A fast Fourier transform is performed on the filtered signal to convert the time-domain signal into a frequency-domain spectrum. The frequency component with the largest amplitude in the 5-45Hz frequency band is searched in the spectrum and defined as the subsynchronous frequency. And extract the amplitude corresponding to the subsynchronous frequency. With phase angle ,in, This represents the intensity of the subsynchronous frequency component in the air gap magnetic field. This indicates the phase information of the component.

[0013] Furthermore, in the S100 air gap magnetic field monitoring and feature extraction, the execution logic for signal redundancy verification and anomaly handling is as follows:

[0014] For the magnetic field signal acquired by the sensor, the characteristic parameters of three sets of subsynchronous frequency components are obtained. , , , , When the amplitude difference between the two sets of parameters exceeds 20% and the phase difference exceeds 30%, either condition is met, and the sensor is judged to be faulty and the signal is abnormal, and the backup sensor channel is automatically activated.

[0015] If the consistency error of the three sets of data is less than 5%, then the average value is taken as the final output parameter, that is: This redundancy verification mechanism ensures that subsequent control circuits provide accurate and stable magnetic field characteristic data;

[0016] When the data does not trigger a fault determination (i.e., amplitude difference ≤ 20% or phase difference ≤ 30%), but the amplitude consistency error of the three sets of data is ≥ 5%, the three sets of data are weighted. The weights are dynamically allocated based on the magnitude of the data deviation, i.e., the weighting coefficients. ,in, For the first The deviation of the set of data from the mean, the final amplitude final phase .

[0017] Furthermore, in the generation of the S200 rotor compensation current command, the expression for the compensation current function is: ,in, This is the dynamic gain coefficient, used to adjust the magnitude of the compensation current. The mutual inductance coefficient between the stator and rotor reflects the degree of electromagnetic coupling between them and converts the air gap magnetic field strength into a corresponding current command. For secondary synchronization frequency, For time variables, By introducing Phase shifting causes the generated compensation current to be out of phase with the subsynchronous frequency component of the air gap magnetic field, which is used to generate a reverse magnetic field on the rotor side to counteract the subsynchronous frequency oscillation of the air gap magnetic field and suppress the subsynchronous oscillation.

[0018] Furthermore, in the S300 dynamic gain adjustment, the gain is adjusted... Dynamic adjustment based on To be updated, among which, This is the updated gain coefficient. The gain coefficient before the update. This is the amplitude of the subsynchronous frequency component of the air gap magnetic field obtained from the current measurement. The magnetic flux density at rated operating conditions is the power frequency flux density of the fan, representing the magnetic field strength of the motor during stable operation. The target magnetic field amplitude is used to suppress the subsynchronous magnetic field component to 0.5% of the power frequency magnetic flux density. This adjustment process dynamically optimizes the strength of the compensation current based on the actual suppression effect. When the suppression effect is poor, the gain is increased to enhance the compensation force; when the suppression effect is good, the gain is maintained or finely adjusted to ensure that the gain parameter matches the system operating conditions. Gain limiting protection is also set. To prevent excessively large or small abnormal values ​​from occurring during the gain adjustment process, upper and lower limits for the gain are set. , When the calculation is obtained At that time, forced Assigned value ,when When, the value is assigned This ensures that the rotor compensation current is always within a safe and controllable range.

[0019] Furthermore, in the S400 current injection and feedforward decoupling, the rotor compensation current command generated in S200 is... The system transforms from a stationary coordinate system to a rotor rotating dq coordinate system, and the current command in the stationary coordinate system is decomposed into two mutually perpendicular d-axis and q-axis compensating current components in the dq coordinate system. And add it to the current loop reference value of the rotor-side converter. , This is used to control the output of the rotor-side converter with corresponding compensation current. Simultaneously, to eliminate the coupling effect between the d and q axis currents and avoid the injection of compensation current affecting the stability of the original vector control, a feedforward decoupling voltage is calculated and injected. ,in, , These are the feedforward decoupling voltages for the d-axis and q-axis, respectively. Slip angular velocity represents the difference between the motor speed and the synchronous speed. The leakage flux coefficient of the motor represents the degree of magnetic leakage in the motor. For rotor inductance, , These are the compensation current components transformed into the dq coordinate system.

[0020] Furthermore, in the S500 suppression verification and policy switching, the formula is used... Calculate the inhibition rate, where, The amplitude of the subsynchronous frequency component of the air gap magnetic field before the injection of compensation current. The amplitude after injection is calculated, and the calculated suppression rate is divided into first-level effect processing, second-level effect processing, and third-level effect processing, and a hierarchical control strategy is implemented.

[0021] Furthermore, in the S500 suppression verification and strategy switching, the hierarchical control strategy is specifically as follows:

[0022] Level 1 effect processing: When At that time, maintain the current gain. The control parameters decoupled from the feedforward remain unchanged to maintain the stable operation of the system. At the same time, the effective control parameters under the current operating conditions are stored in the historical database to provide a reference for rapid control under similar operating conditions in the future.

[0023] Secondary effect processing: When For gain coefficient Perform dynamic adjustments and recalculate the rotor compensation current command. And inject new compensation current through S400;

[0024] Level 3 effect processing: When At that time, a frequency-doubled auxiliary signal is added to the original compensation current, that is... The frequency component and auxiliary signal amplitude are set to 30%-50% of the current compensation current amplitude.

[0025] Compared with existing technologies, this method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system has the following advantages:

[0026] I. This invention achieves subsynchronous oscillation suppression at the electromagnetic level. By real-time monitoring of the subsynchronous component of the air gap magnetic field and injecting a counter-phase compensation current on the rotor side, the stator and rotor magnetic fields actively interfere and cancel each other in the subsynchronous frequency band, directly blocking the energy transfer path of the subsynchronous oscillation and destroying the conditions for oscillation formation. The dynamic gain adjustment mechanism optimizes the compensation intensity based on the real-time suppression effect. The triple decision logic combined with the high-frequency auxiliary signal strategy can cope with the frequency variation of subsynchronous oscillation from 5-45Hz, avoiding the problem of insufficient adaptability of fixed parameter control to frequency drift, and improving the universality and effectiveness of the suppression strategy.

[0027] Second, this invention constructs a highly adaptive control system. A three-axis Hall sensor array collects data in real time, and after bandpass filtering and FFT analysis, it provides accurate parameters for calculating the compensation current. The dynamic gain is adjusted in real time according to the suppression rate feedback to ensure that the compensation intensity matches the oscillation degree. Feedforward decoupling control eliminates dq-axis current coupling and ensures the accuracy of current injection. The effect verification stage makes decisions based on the suppression rate to realize dynamic switching of control strategies. All stages form a complete system of monitoring, calculation, execution and feedback, enabling the system to respond quickly to changes in grid conditions and wind turbine operating status. It can continuously and stably suppress subsynchronous oscillations under complex conditions without manual intervention, thereby improving the autonomous adjustment capability and operational stability of the doubly fed grid system.

[0028] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0030] Figure 1 This is a flowchart illustrating the operation of a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system.

[0031] Figure 2This is a step-by-step framework diagram of a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system. Detailed Implementation

[0032] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0033] Example 1

[0034] This embodiment provides a specific implementation method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system, such as... Figure 2 As shown, this method forms a complete control system through steps such as air gap magnetic field monitoring and feature extraction, rotor compensation current command generation, dynamic gain adjustment, current injection and feedforward decoupling, and suppression verification and strategy switching. It effectively suppresses the subsynchronous oscillation of the doubly fed grid system from the electromagnetic essence level, and is used to cope with complex and ever-changing power grid operating conditions.

[0035] First, the air gap magnetic field monitoring and feature extraction stage (S100) is entered. A triaxial Hall sensor array is arranged at 120° mechanical angle intervals along the circumferential direction of the air gap between the stator and rotor of the doubly fed wind turbine. Each sensor group contains three mutually perpendicular Hall elements (X, Y, Z) used to synchronously acquire the vector components of the air gap magnetic field in three-dimensional space. Based on the Hall effect, the triaxial Hall sensor array converts changes in magnetic field strength into voltage signals. Its sampling frequency is set to 20kHz to meet the sampling requirements of the subsynchronous frequency (5-45Hz). The acquired raw magnetic field signal contains power frequency and its harmonic interference, high-frequency mechanical vibration noise, etc., and is input to a bandpass filter. In this embodiment, the passband range of the bandpass filter is set to 5-45Hz, which can effectively filter out interference and output a clean subsynchronous frequency band magnetic field signal. A fast Fourier transform is performed on the filtered signal to weight the signal and reduce spectral leakage. By converting the time-domain signal to a frequency-domain spectrum, the frequency component with the largest amplitude within the frequency band is searched in the spectrum and defined as the subsynchronous frequency. And extract the amplitude corresponding to the subsynchronous frequency. With phase angle To improve frequency estimation accuracy, signal redundancy verification and anomaly handling are performed: characteristic parameters of three sets of subsynchronous frequency components are obtained. , , When the amplitude difference between any two sets of parameters exceeds 20% or the phase difference exceeds 30%, it is determined to be a sensor malfunction or signal abnormality, and the backup sensor channel is automatically activated. If the consistency error of the three sets of data is less than 5%, the average value is taken as the final output parameter. When the data does not trigger a fault determination (i.e., amplitude difference ≤ 20% or phase difference ≤ 30%), but the amplitude consistency error of the three sets of data is ≥ 5%, the three sets of data are weighted. The weights are dynamically allocated according to the magnitude of the data deviation, i.e., the weighting coefficients. ,in, For the first The deviation of the set of data from the mean, the final amplitude final phase This ensures that accurate and stable magnetic field characteristic data are provided for subsequent control processes.

[0036] Then, the rotor compensation current command generation stage (S200) is entered, based on the amplitude of the subsynchronous frequency component extracted in S100. and phase angle and the dynamic gain coefficient provided by S300 Based on the mutual inductance characteristics of the stator and rotor of a doubly-fed induction generator (DFIG), a compensation current function is established based on magnetomotive force balance, and the mutual inductance coefficients of the stator and rotor are calculated. The electromagnetic coupling degree between the stator and rotor is determined as follows: Equivalent circuit parameters of the motor are obtained through no-load and locked-rotor experiments, and calculated based on motor magnetic circuit theory. During the operation of the wind turbine, the least squares method is used to... Online identification is performed by collecting real-time data such as stator voltage and current, and rotor voltage and current. Identification equations are constructed based on the dynamic mathematical model of the doubly-fed motor and iteratively updated. The estimated value is used to compensate for parameter drift caused by factors such as motor temperature changes and magnetic circuit saturation. The expression for the compensation current function is as follows: ,in, This is the dynamic gain coefficient, used to adjust the magnitude of the compensation current. By introducing a 180° phase offset, the generated compensation current is out of phase with the subsynchronous frequency component of the air gap magnetic field, thereby generating a reverse magnetic field on the rotor side to cancel the subsynchronous frequency oscillation of the air gap magnetic field and suppress the subsynchronous oscillation. In this embodiment, when generating the compensation current command, the command amplitude needs to be limited to avoid the system overcurrent caused by excessive compensation current. When the calculated amplitude exceeds 120% of the rated current of the rotor-side converter, it is limited to 120% of the rated current. When the amplitude is less than 10% of the rated current, it is limited to 10% of the rated current to ensure the safe and stable operation of the system.

[0037] Next, the system enters the dynamic gain adjustment phase (S300). During system operation, the system adjusts the gain based on the suppression rate fed back from S500. And the set target magnetic field amplitude, affecting the gain Dynamic adjustments are made, and the target magnetic field amplitude is set to... ,in The gain is the power frequency magnetic flux density under rated operating conditions of the wind turbine during the initial operation of the system. Set as To provide sufficient compensation current during system startup and in the event of sudden oscillations, and to quickly respond to the suppression requirements of subsynchronous oscillations, the dynamic adjustment formula is as follows: ,in This is the updated gain coefficient. The gain coefficient before the update. This is the amplitude of the subsynchronous frequency component of the air gap magnetic field currently measured. This adjustment process dynamically optimizes the strength of the compensation current based on the actual suppression effect. When the suppression effect is poor, the gain is increased to enhance the compensation strength; when the suppression effect is good, the gain is maintained or fine-tuned to ensure that the gain parameter matches the system operating conditions. To prevent excessively large or small abnormal values ​​from occurring during the gain adjustment process, upper and lower limits for the gain are set. When the calculation is obtained At that time, forced Assigned value ,when When, the value is assigned This ensures that the rotor compensation current is always within a safe and controllable range.

[0038] Then, the current injection and feedforward decoupling stage (S400) begins, where the rotor compensation current command generated in S200 is applied. The transformation from the stationary coordinate system to the rotor rotating dq coordinate system is based on the mathematical model of the doubly-fed motor in the synchronously rotating dq coordinate system, and involves changing the angle. Rotor mechanical angle measured by rotor position sensor Number of pole pairs of the motor Calculated, i.e. By transforming coordinates, the current command in the stationary coordinate system is decomposed into mutually perpendicular d-axis and q-axis compensation current components in the dq coordinate system. , ,Will and Reference values ​​superimposed on the rotor-side converter current loop and To avoid system shocks caused by sudden current changes during the superposition process, and to eliminate the coupling effect between the d and q axis currents, and to prevent the compensation current injection from affecting the stability of the original vector control, a feedforward decoupling voltage is calculated and injected. ,in, The slip angular velocity is determined by the grid synchronization frequency. With rotor electric angular velocity Calculated, i.e. , is the leakage flux coefficient of the motor. As the rotor inductor, the rotor voltage reference value, after coordinate transformation, current superposition, and decoupling, is used to generate six pulse signals through space vector pulse width modulation to inject compensation current and compensate for subsynchronous oscillation.

[0039] Finally, the suppression verification and strategy switching phase (S500) begins. 200ms after the compensation current injection, the amplitude of the subsynchronous frequency component of the air gap magnetic field is measured again using a triaxial Hall sensor array. The 200ms evaluation time interval is chosen to comprehensively consider the time constant of the doubly-fed wind turbine's electromechanical transient process and the control system's sampling period, ensuring the system responds adequately to the compensation current. This is confirmed by the formula... Calculate the inhibition rate, where The amplitude of the subsynchronous frequency component of the air gap magnetic field before the injection of compensation current. To determine the amplitude after injection, double-precision floating-point arithmetic was used in the calculation process, and multiple verifications were performed to ensure that the result error was less than [value missing]. The calculated inhibition rate is divided into three levels, and a hierarchical control strategy is implemented:

[0040] Level 1 effect processing: When At that time, maintain the current gain. The control parameters decoupled from the feedforward remain unchanged to maintain the stable operation of the system. At the same time, the effective control parameters under the current operating conditions are stored in the historical database to provide a reference for rapid control under similar operating conditions in the future.

[0041] Secondary effect processing: When For gain coefficient Perform dynamic adjustments and recalculate the rotor compensation current command. And inject new compensation current through S400;

[0042] Level 3 effect processing: When At that time, a frequency-doubled auxiliary signal is added to the original compensation current, that is... The frequency component and the amplitude of the auxiliary signal are set to 30%-50% of the current compensation current amplitude. The phase is kept synchronized with the subsynchronous oscillation signal through a phase-locked loop, which enhances the ability to suppress complex subsynchronous oscillations.

[0043] In summary, this embodiment details the complete implementation process of a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system. This method accurately obtains key parameters of the subsynchronous oscillations through air gap magnetic field monitoring and feature extraction. Based on these parameters, a rotor compensation current command is generated, forming a reverse magnetic field to suppress oscillations from an electromagnetic perspective. A dynamic gain adjustment mechanism ensures that the compensation intensity matches the actual operating conditions. Current injection and feedforward decoupling ensure accurate injection of the compensation current. Suppression verification and strategy switching achieve dynamic optimization of the control strategy. Each step is closely linked, forming a complete system of monitoring, calculation, execution, and feedback. This method actively suppresses subsynchronous oscillations from an electromagnetic perspective, possesses adaptive adjustment capabilities, effectively copes with complex and changing grid operating conditions, improves the stability and safety of the doubly-fed grid-connected system, and provides strong support for the safe and reliable operation of doubly-fed wind turbines.

[0044] Example 2

[0045] like Figure 1 As shown, this embodiment provides a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system. The specific steps of this method are as follows:

[0046] (1) Air gap magnetic field monitoring and feature extraction

[0047] A triaxial Hall sensor array is arranged in the circumferential direction of the air gap between the stator and rotor of the doubly fed wind turbine. Each sensor group contains three mutually perpendicular Hall elements in X, Y and Z directions, and synchronously collects the vector components of the air gap magnetic field in three-dimensional space at a sampling frequency of 20kHz.

[0048] The acquired raw magnetic field signal is input into a bandpass filter to filter out power frequency and harmonic interference and high-frequency mechanical vibration noise, thus obtaining a pure subsynchronous frequency band magnetic field signal.

[0049] The filtered signal is subjected to a fast Fourier transform to convert the time-domain signal into a frequency-domain spectrum. The frequency component with the largest amplitude in the 5-45Hz frequency band is searched and determined as the subsynchronous frequency. The amplitude and phase angle corresponding to the subsynchronous frequency are then extracted.

[0050] Redundancy verification and anomaly handling are performed on the magnetic field signals collected by the sensor: three sets of subsynchronous frequency characteristic parameters are obtained. If the amplitude difference between two sets of parameters exceeds 20% and the phase difference exceeds 30°, it is determined that the sensor is faulty or the signal is abnormal, and the backup sensor channel is activated. If the consistency error of the three sets of data is less than 5%, the average value is taken as the final output parameter.

[0051] (2) Generation of rotor compensation current command

[0052] Based on the amplitude, phase angle, and dynamic gain coefficient of the subsynchronous frequency component, and combined with the mutual inductance characteristics of the stator and rotor of the doubly fed wind turbine, a compensation current function is established based on the magnetomotive force balance to generate the rotor compensation current command.

[0053] The compensation current function introduces a phase shift, causing the generated compensation current to be out of phase with the subsynchronous frequency component of the air gap magnetic field, thereby generating a reverse magnetic field on the rotor side to cancel the subsynchronous frequency oscillation of the air gap magnetic field.

[0054] (3) Dynamic gain adjustment

[0055] When the system is initially running, the gain is set to 1.2 so that it can quickly provide compensation current to respond to the need to suppress subsynchronous oscillations when the system starts up and when sudden oscillations occur.

[0056] During system operation, the gain is dynamically adjusted based on the suppression rate of the suppression verification and strategy switching feedback, as well as the set target magnetic field amplitude, to generate a new gain coefficient, which is then transmitted to the rotor compensation current command generation stage for command generation in the next control cycle.

[0057] Set up gain limiting protection. When the calculated new gain is greater than the upper limit of 2.0 or less than the lower limit of 0.5, force it to be assigned the upper or lower limit respectively to ensure that the rotor compensation current command is within a safe and controllable range.

[0058] (4) Current injection and feedforward decoupling

[0059] The generated rotor compensation current command is transformed from the stationary coordinate system to the rotor rotating dq coordinate system, decomposed into d-axis and q-axis compensation current components, and superimposed on the current loop reference value of the rotor-side converter to control the rotor-side converter to output the corresponding compensation current.

[0060] Calculate and inject the feedforward decoupling voltage to eliminate the coupling effect between the dq axis currents and avoid the impact of compensation current injection on the stability of the original vector control.

[0061] (5) Suppressing verification and policy switching

[0062] After 200ms of compensation current injection, the amplitude of the subsynchronous frequency component of the air gap magnetic field is remeasured using a triaxial Hall sensor array, and the suppression rate is calculated.

[0063] (6) Implement a graded control strategy based on the inhibition rate:

[0064] If the suppression rate is ≥85%, the control parameters of the current gain and feedforward decoupling remain unchanged to maintain stable system operation, and the effective control parameters under the current operating conditions are stored in the historical database.

[0065] If 60% ≤ suppression rate < 85%, the gain coefficient is dynamically adjusted, the rotor compensation current command is recalculated, and a new compensation current is injected.

[0066] If the suppression rate is less than 60%, add a frequency-doubled auxiliary signal to the original compensation current. The amplitude of the auxiliary signal is set to 30%-50% of the current compensation current amplitude.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system, characterized in that, The specific steps of this method are as follows: S100, Air Gap Magnetic Field Monitoring and Feature Extraction: A triaxial Hall sensor array is used to acquire air gap magnetic field signals in real time. The acquired signals are bandpass filtered and subjected to spectrum analysis to extract the amplitude of the subsynchronous frequency component. and phase angle And perform signal redundancy verification and anomaly handling; S200, Rotor compensation current command generation: based on the amplitude of the subsynchronous frequency component. Phase angle and the dynamic gain coefficient provided by S300 A compensation current function is established based on magnetomotive force balance, and a rotor compensation current command is generated. ; S300, Dynamic Gain Adjustment: During initial system startup, the gain is adjusted... Set as It provides compensation current during system startup and in the event of sudden oscillations. During system operation, it adjusts the current based on the suppression rate fed back by the S500. And the set target magnetic field amplitude, affecting the gain Dynamically adjust to generate new gain coefficients and will The instruction is passed to S200 for the generation of the next control cycle; S400, Current Injection and Feedforward Decoupling: Decoupling the Compensation Current Command The signal is converted into a control signal and injected into the system. It is then superimposed on the reference value of the rotor-side converter current loop to calculate the feedforward decoupling voltage to eliminate dq-axis current coupling and compensate for subsynchronous oscillation. S500, Suppression Verification and Strategy Switching: 200ms after the compensation current injection, the amplitude of the subsynchronous frequency component of the air gap magnetic field is measured again using a triaxial Hall sensor array, and the suppression rate is calculated. A hierarchical control strategy is executed based on the inhibition rate.

2. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 1, characterized in that, In the S100 air gap magnetic field monitoring and feature extraction, a triaxial Hall sensor array is arranged along the circumferential direction of the air gap between the stator and rotor of the doubly fed wind turbine. Each sensor group contains three mutually perpendicular Hall elements (X, Y, and Z) used to synchronously acquire the vector components of the air gap magnetic field in three-dimensional space. The sampling frequency of the triaxial Hall sensor array is set to 20kHz. The acquired raw magnetic field signal is input to a bandpass filter, and a clean subsynchronous frequency band magnetic field signal is output. A fast Fourier transform is performed on the filtered signal to convert the time-domain signal into a frequency-domain spectrum. The frequency component with the largest amplitude in the 5-45Hz band is searched in the spectrum and defined as the subsynchronous frequency. And extract the amplitude corresponding to the subsynchronous frequency. With phase angle ,in, This represents the intensity of the subsynchronous frequency component in the air gap magnetic field. This indicates the phase information of the component.

3. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 2, characterized in that, The execution logic for signal redundancy verification and anomaly handling in the S100 air gap magnetic field monitoring and feature extraction is as follows: For the magnetic field signal acquired by the sensor, the characteristic parameters of three sets of subsynchronous frequency components are obtained. , , , , When the amplitude difference between any two sets of parameters exceeds 20% and the phase difference exceeds 30%, either of these conditions is met, and the sensor is judged to be faulty and the signal is abnormal, and the backup sensor channel is automatically activated. When the consistency error of the three sets of data is less than 5%, the average value is taken as the final output parameter, that is: ; When the data does not trigger a fault determination, but the amplitude consistency error of the three sets of data is ≥5%, the three sets of data are weighted. The weights are dynamically allocated according to the magnitude of the data deviation, i.e., the weight coefficients. ,in, For the first The deviation of the set of data from the mean, the final amplitude final phase .

4. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 1, characterized in that, In the generation of the S200 rotor compensation current command, the expression of the compensation current function is: ,in, This is the dynamic gain coefficient, used to adjust the magnitude of the compensation current. The mutual inductance coefficient between the stator and rotor reflects the degree of electromagnetic coupling between them and converts the air gap magnetic field strength into a corresponding current command. For secondary synchronization frequency, For time variables, By introducing Phase shifting causes the generated compensation current to be out of phase with the subsynchronous frequency component of the air gap magnetic field, which is used to generate a reverse magnetic field on the rotor side to counteract the subsynchronous frequency oscillation of the air gap magnetic field and suppress the subsynchronous oscillation.

5. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 1, characterized in that, In the S300 dynamic gain adjustment, the gain is adjusted accordingly. Dynamic adjustment based on To be updated, among which, This is the updated gain coefficient. The gain coefficient before the update. This is the amplitude of the subsynchronous frequency component of the air gap magnetic field obtained from the current measurement. The magnetic flux density at rated operating conditions is the power frequency flux density of the fan, representing the magnetic field strength of the motor during stable operation. The target magnetic field amplitude is used to suppress the subsynchronous magnetic field component to 0.5% of the power frequency magnetic flux density, and gain limiting protection is set, with upper and lower limits for gain: , When the calculation is obtained At that time, forced Assigned value ,when When, the value is assigned .

6. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 1, characterized in that, In the S400 current injection and feedforward decoupling process, the rotor compensation current command generated by S200 is... The system transforms from a stationary coordinate system to a rotor rotating dq coordinate system, and the current command in the stationary coordinate system is decomposed into two mutually perpendicular d-axis and q-axis compensating current components in the dq coordinate system. And add it to the current loop reference value of the rotor-side converter. , It is used to control the output of the rotor-side converter to provide corresponding compensation current. At the same time, it calculates and injects feedforward decoupling voltage. ,in, , These are the feedforward decoupling voltages for the d-axis and q-axis, respectively. Slip angular velocity represents the difference between the motor speed and the synchronous speed. The leakage flux coefficient of the motor represents the degree of magnetic leakage in the motor. For rotor inductance, , These are the compensation current components transformed into the dq coordinate system.

7. The method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 1, characterized in that, In the S500 suppression verification and policy switching, the formula is used... Calculate the inhibition rate, where, The amplitude of the subsynchronous frequency component of the air gap magnetic field before the injection of compensation current. The amplitude after injection is calculated, and the calculated suppression rate is divided into first-level effect processing, second-level effect processing, and third-level effect processing, and a hierarchical control strategy is implemented.

8. A method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system according to claim 7, characterized in that, In the S500 suppression verification and strategy switching, the hierarchical control strategy is as follows: Level 1 effect processing: When At that time, maintain the current gain. The control parameters decoupled from the feedforward remain unchanged to maintain the stable operation of the system. At the same time, the effective control parameters under the current operating conditions are stored in the historical database. Secondary effect processing: When For gain coefficient Perform dynamic adjustments and recalculate the rotor compensation current command. And inject new compensation current through S400; Level 3 effect processing: When At that time, a frequency-doubled auxiliary signal is added to the original compensation current, that is... The frequency component and auxiliary signal amplitude are set to 30%-50% of the current compensation current amplitude.

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