Method for suppressing subsynchronous oscillation of doubly-fed grid-connected system

Abstract

The invention discloses a method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system, and relates to the technical field of stability control of a power system, and the method comprises the specific steps: S100, extracting the amplitude and phase angle of a subsynchronous frequency component, S200, generating a rotor compensation current instruction according to the amplitude and phase angle of the subsynchronous frequency component and a dynamic gain, and S200, generating a rotor compensation current instruction according to the rotor compensation current instruction; s300, dynamically adjusting the gain according to the suppression ratio and the amplitude of the target magnetic field during operation, S400, calculating the feed-forward decoupling voltage, S500, calculating the suppression ratio after injection, and executing a hierarchical control strategy. Subsynchronous oscillation suppression from the electromagnetic essential level is realized, and by monitoring the subsynchronous component of the air-gap magnetic field in real time and injecting the anti-phase compensation current at the rotor side, the suppression efficiency of the subsynchronous oscillation is improved. Active interference of a stator magnetic field and a rotor magnetic field in a subsynchronous frequency band is cancelled, an energy transfer path of subsynchronous oscillation is directly blocked, oscillation forming conditions are destroyed, and a dynamic gain adjustment mechanism optimizes compensation intensity according to a real-time suppression effect so as to cope with 5-45Hz subsynchronous oscillation frequency change.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability control, and in particular to a method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system. Background Art

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

[0003] In the existing technology, the suppression methods for DFIG subsynchronous oscillations are mainly divided into two categories: passive suppression (such as adding a damping filter) and active control (such as additional damping control of the converter). However, the passive suppression scheme has significant defects: the damping filter needs to be designed for a specific oscillation frequency. When the grid operating conditions change, the filter parameter mismatch causes the suppression effect to decay. The hardware installation increases the system cost and volume, and is not compatible with the wind turbines that have been put into operation. Although the active control scheme realizes dynamic suppression by injecting compensation current through the converter, the existing technology uses a fixed-parameter PI controller, which has limited response speed and anti-interference ability. Especially in the scenario where multi-modal oscillations coexist, the compensation current phase lag or amplitude overshoot is prone to occur, and manual intervention is required to adjust the control parameters, which makes it difficult to meet the unmanned operation and maintenance requirements of the wind farm.

[0004] In summary, existing subsynchronous oscillation suppression technologies have problems such as poor adaptability and insufficient control accuracy, making it difficult to effectively cope with complex and changeable grid operating conditions. Therefore, there is an urgent need for a new method that can actively suppress subsynchronous oscillations from the electromagnetic essence level, while having adaptive adjustment capabilities and high reliability, in order to improve the stability and safety of the doubly fed grid-connected system. Summary of the Invention

[0005] The purpose of the present invention is to make up for the shortcomings of the existing technology and provide a method for suppressing subsynchronous oscillations in a doubly fed grid-connected system. The method can realize subsynchronous oscillation suppression from the electromagnetic essence level. By real-time monitoring of the subsynchronous component of the air gap magnetic field and injecting anti-phase compensation current on the rotor side, the stator and rotor magnetic fields actively interfere with 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 according to the real-time suppression effect. The triple decision logic is combined with the high-frequency auxiliary signal strategy to cope with 5-45Hz subsynchronous oscillation frequency changes, avoid the problem of insufficient adaptability of fixed parameter control to frequency drift, and improve the universality and effectiveness of the suppression strategy.

[0006] In order to solve the above technical problems, the present invention provides the following technical solution: a method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system, the specific steps of the method are as follows: S100, air gap magnetic field monitoring and feature extraction: Based on the air gap magnetic field anomaly caused by subsynchronous oscillation during the operation of the doubly fed wind turbine, a three-axis Hall sensor array is used to collect the air gap magnetic field signal in real time. The collected signal is band-pass 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 check and exception processing; S200, rotor compensation current command generation: according to the amplitude of the subsynchronous frequency component and phase angle And the dynamic gain coefficient provided by S300 , 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 and a rotor side compensation current instruction is generated ; S300, dynamic gain adjustment: When the system is initially running, the gain Set to , when the system starts and when sudden oscillation occurs, it provides compensation current and quickly responds to the suppression demand of subsynchronous oscillation. During the operation of the system, according to the suppression rate fed back by S500 As well as the target magnetic field amplitude, the gain Dynamically adjust to generate new gain coefficients , and Passed to S200 for command generation for the next control cycle; S400, current injection and feedforward decoupling: the compensation current instruction Convert it into a control signal and inject it into the system, superimpose it on the rotor-side converter current loop reference value, calculate the feedforward decoupling voltage to eliminate the dq axis current coupling, and compensate for subsynchronous oscillation; S500, suppression verification and strategy switching: After 200ms of compensation current injection, the air gap magnetic field sensor array is used again to measure the amplitude of the subsynchronous component of the air gap magnetic field and calculate the suppression rate. , a hierarchical control strategy is executed according to the inhibition rate.

[0007] Furthermore, in the S100 air gap magnetic field monitoring and feature extraction, a three-axis 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 group of sensors contains three mutually perpendicular Hall elements of X, Y, and Z, which are used to synchronously collect the vector components of the air gap magnetic field in three-dimensional space. The sampling frequency of the Hall sensor is set to 20kHz, and the collected original magnetic field signal is input into the bandpass filter. Through filtering processing, the power frequency and its harmonic interference, as well as high-frequency mechanical vibration noise are effectively filtered out, and a pure 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 oscillation dominant frequency. , and extract the amplitude corresponding to the frequency and phase angle ,in, represents the intensity of the subsynchronous frequency component in the air gap magnetic field, Indicates the phase information of this component.

[0008] Furthermore, in the S100 air gap magnetic field monitoring and feature extraction, the execution logic of signal redundancy check and exception handling is: For the magnetic field signal collected by the sensor, obtain three sets of sub-synchronous characteristic parameters 、 , , 、 When the amplitude difference of the two sets of parameters exceeds 20% or the phase difference exceeds 30%, it is determined to be a sensor failure and signal abnormality, 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: ,This redundancy check mechanism ensures that the subsequent control links provide accurate and stable ,magnetic field characteristic data; When the data does not trigger a fault judgment, that is, the amplitude difference is ≤20% or the phase difference is ≤30%, but the amplitude consistency error of the three sets of data is ≥5%, the three sets of data are weighted and the weights are dynamically allocated according to the size of the data deviation, that is, the weight coefficient ,in, For the Deviation of group data from the mean, final amplitude , the final phase .

[0009] Furthermore, in the S200 rotor compensation current command generation, the expression of the compensation current function is: ,in, is the dynamic gain coefficient, which is used to adjust the compensation current. is the mutual inductance coefficient between the stator and rotor, which is used to reflect the degree of electromagnetic coupling between the stator and rotor, and convert the air gap magnetic field strength into the corresponding current instruction size. is the subsynchronous oscillation frequency, is the time variable, By introducing The phase shift makes the generated compensation current anti-phase with the subsynchronous component of the air gap magnetic field, which is used to generate a reverse magnetic field on the rotor side to offset the subsynchronous oscillation of the air gap magnetic field and suppress the subsynchronous oscillation.

[0010] Furthermore, in the dynamic gain adjustment of S300, the gain The dynamic adjustment is based on Update, where is the updated gain coefficient, is the gain coefficient before updating, is the amplitude of the subsynchronous component of the air gap magnetic field currently measured, It is the power frequency magnetic flux density under rated working conditions of the fan, indicating the magnetic field strength of the motor when it is running stably. 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 is used to dynamically optimize 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 parameters match the system operating conditions. Gain limiting protection is also set. To prevent abnormal values ​​that are too large or too small during the gain adjustment process, the upper and lower gain limits are set: , , when the calculated When forced to Assigned to ,when When , the value is , ensuring that the rotor side compensation current is always within a safe and controllable range.

[0011] Furthermore, the S400 current injection and feedforward decoupling are used to convert the rotor compensation current command generated by S200 into Convert from the stationary coordinate system to the rotor rotating dq coordinate system, and decompose the current instruction in the stationary coordinate system into two mutually perpendicular d-axis and q-axis compensation current components in the dq coordinate system. , and add it to the current loop reference value of the rotor-side converter 、 , which is used to control the rotor-side converter to output the corresponding compensation current. At the same time, in order to eliminate the coupling effect between the dq axis currents and avoid the compensation current injection affecting the stability of the original vector control, the feedforward decoupling voltage is calculated and injected ,in, 、 are the feedforward decoupling voltages of the d-axis and q-axis respectively, is the slip angular velocity, which indicates the difference between the motor speed and the synchronous speed. is the magnetic leakage coefficient of the motor, which indicates the degree of magnetic leakage of the motor. is the rotor inductance, 、 are the compensation current components converted to the dq coordinate system respectively.

[0012] Furthermore, in the S500 suppression verification and policy switching, the formula Calculate the inhibition rate, where is the amplitude of the subsynchronous component of the air gap magnetic field before the compensation current is injected, is the amplitude after injection, and the calculated inhibition rate is divided into primary effect processing, secondary effect processing, and tertiary effect processing, and a hierarchical control strategy is implemented.

[0013] Furthermore, in the S500 suppression verification and strategy switching, the hierarchical control strategy is specifically as follows: First level effect processing: When When the current gain is maintained The control parameters of the feedforward decoupling remain unchanged to maintain the stable operation of the system. At the same time, the effective control parameters under the current working conditions are stored in the historical database to provide a reference for rapid control under similar working conditions in the future. Secondary effect processing: When , for the gain coefficient Perform dynamic adjustment and recalculate the rotor compensation current command and inject new compensation current through S400; Three-level effect processing: When , a 2-fold frequency auxiliary signal is added to the original compensation current, that is, Frequency component, the auxiliary signal amplitude is set to 30%-50% of the current compensation current amplitude.

[0014] Compared with the prior art, this method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system has the following beneficial effects: The present invention realizes the suppression of subsynchronous oscillations at the level of electromagnetic essence. By real-time monitoring of the subsynchronous component of the air gap magnetic field and injecting anti-phase compensation current on the rotor side, the stator and rotor magnetic fields actively interfere with 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 strength according to the real-time suppression effect. The triple decision logic combined with the high-frequency auxiliary signal strategy can cope with the frequency changes of 5-45Hz subsynchronous oscillations, avoid the problem of insufficient adaptability of fixed parameter control to frequency drift, and improve the universality and effectiveness of the suppression strategy.

[0015] The present invention constructs a highly adaptive control system. The air gap magnetic field sensor array collects data in real time, and provides precise parameters for compensation current calculation through bandpass filtering and FFT analysis. The dynamic gain is adjusted in real time according to the suppression rate feedback to ensure that the compensation intensity matches the oscillation degree. The feedforward decoupling control eliminates the dq axis current coupling and guarantees the accuracy of current injection. The effect verification link makes decisions based on the suppression rate graded to achieve dynamic switching of the control strategy. Each link forms a complete system of monitoring, calculation, execution and feedback, so that the system can quickly respond to changes in the grid conditions and the operating status of the wind turbine. It can continuously and stably suppress subsynchronous oscillations under complex conditions without human intervention, thereby improving the autonomous adjustment capability and operating stability of the doubly fed grid-connected system.

[0016] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0018] Figure 1 An operational flow chart of a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system; Figure 2 A framework diagram of the steps of a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system. DETAILED DESCRIPTION

[0019] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0020] Example 1 This embodiment provides a specific implementation method of a method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system, such as Figure 2 As shown in the figure, this method forms a complete control system through the steps of air gap magnetic field monitoring and feature extraction, rotor compensation current command generation, dynamic gain adjustment, current injection and feedforward decoupling, suppression verification and strategy switching, etc., which can effectively suppress the subsynchronous oscillation of the doubly fed grid-connected system from the electromagnetic essence level, and can be used to cope with complex and changeable grid operating conditions.

[0021] First, the air gap magnetic field monitoring and feature extraction stage (S100) is entered. A three-axis Hall sensor array is arranged at intervals of 120° mechanical angle in the circumferential direction of the air gap between the stator and rotor of the doubly fed wind turbine. Each group of sensors includes three mutually perpendicular Hall elements of X, Y, and Z, which are used to synchronously collect the vector components of the air gap magnetic field in three-dimensional space. The Hall sensor converts the change in magnetic field intensity into a voltage signal based on the Hall effect. Its sampling frequency is set to 20kHz, which meets the sampling requirements of the subsynchronous frequency (5-45Hz). The collected original magnetic field signal contains power frequency and its harmonic interference, high-frequency mechanical vibration noise, etc., which is input into 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 pure subsynchronous frequency band magnetic field signal. Fast Fourier transform is performed on the filtered signal, and the signal is weighted to reduce spectral leakage. By converting the time domain signal into a frequency domain spectrum, the frequency component with the largest amplitude in the frequency band is searched in the spectrum and defined as the subsynchronous oscillation dominant frequency. , and extract the amplitude corresponding to the frequency and phase angle ,In order to improve the frequency estimation accuracy, signal redundancy check and exception processing are performed: ,obtain the sub-synchronous characteristic parameters collected by three groups of sensors 、 、 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 failure 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, that is, When the data does not trigger a fault judgment, that is, the amplitude difference is ≤20% or the phase difference is ≤30%, but the amplitude consistency error of the three sets of data is ≥5%, the three sets of data are weighted and the weights are dynamically allocated according to the size of the data deviation, that is, the weight coefficient ,in, For the Deviation of group data from the mean, final amplitude , the final phase , ensuring that accurate and stable magnetic field characteristic data is provided for subsequent control links.

[0022] Then, the rotor compensation current instruction generation stage (S200) is entered, and the sub-synchronous frequency component amplitude extracted in S100 is used to generate the rotor compensation current instruction. and phase angle , and the dynamic gain coefficient provided by S300 , combined with the mutual inductance characteristics of the stator and rotor of the doubly fed wind turbine, the compensation current function is established based on the magnetomotive force balance, and the mutual inductance coefficient of the stator and rotor is Reflects the degree of electromagnetic coupling between the stator and rotor. The determination process is as follows: The motor equivalent circuit parameters are obtained through no-load test and locked-rotor test, and the motor magnetic circuit theory is used to calculate the equivalent circuit parameters. During the operation of the fan, the least square method is used to Perform online identification, collect real-time data such as stator voltage, current, rotor voltage, current, etc., build identification equations based on the dynamic mathematical model of the doubly fed motor, and iteratively update To compensate for the parameter drift caused by factors such as motor temperature change and magnetic circuit saturation, the expression of the compensation current function is: ,in, is the dynamic gain coefficient, which is used to adjust the compensation current. By introducing a 180° phase offset, the generated compensation current is made anti-phase with the subsynchronous component of the air gap magnetic field, thereby generating a reverse magnetic field on the rotor side that offsets the subsynchronous oscillation of the air gap magnetic field and suppresses the subsynchronous oscillation. When generating the compensation current command in this embodiment, the command amplitude needs to be limited to avoid excessive compensation current causing system overcurrent. 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 safe and stable operation of the system.

[0023] Then, the dynamic gain adjustment phase (S300) is entered. During the system operation, the suppression rate is fed back from S500. As well as the target magnetic field amplitude, the gain Dynamic adjustment is performed, and the target magnetic field amplitude is set to ,in is the power frequency magnetic flux density under rated working condition of the fan. When the system is initially running, the gain Set to , to provide sufficient compensation current when the system starts and when sudden oscillation occurs, and quickly respond to the suppression requirements of subsynchronous oscillations. The dynamic adjustment formula is: ,in is the updated gain coefficient, is the gain coefficient before updating, The amplitude of the subsynchronous component of the air gap magnetic field is currently measured. This adjustment process dynamically optimizes the intensity of the compensation current according to 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 parameters match the system operating conditions. To prevent abnormal values ​​that are too large or too small during the gain adjustment process, the upper and lower gain limits are set: , when the calculated When forced to Assigned to ,when When , the value is , ensuring that the rotor side compensation current is always within a safe and controllable range.

[0024] After that, the current injection and feedforward decoupling phase (S400) is entered, and the rotor compensation current command generated by S200 is converted to From the stationary coordinate system to the rotor rotating dq coordinate system, the coordinate transformation is based on the mathematical model of the doubly fed machine in the synchronous rotating dq coordinate system, and the angle is transformed. The rotor mechanical angle measured by the rotor position sensor Number of motor pole pairs Calculated, that is By coordinate transformation, the current command in the stationary coordinate system is decomposed into d-axis and q-axis compensation current components that are perpendicular to each other in the dq coordinate system. 、 ,Will and The reference values ​​superimposed on the rotor-side converter current loop are and In order to avoid the system shock caused by the current mutation during the superposition process, in order to eliminate the coupling effect between the dq axis current and avoid the compensation current injection affecting the stability of the original vector control, the feedforward decoupling voltage is calculated and injected ,in, is the slip angular velocity, synchronized with the grid frequency and rotor electrical angular velocity Calculated, that is , is the leakage flux coefficient of the motor, For the rotor inductance, 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 realize the injection of compensation current and compensate for the subsynchronous oscillation.

[0025] Finally, the suppression verification and strategy switching stage (S500) is entered. After 200ms of the compensation current injection, the air gap magnetic field sensor array is used again to measure the amplitude of the subsynchronous component of the air gap magnetic field. 200ms is selected as the evaluation time interval. This is to comprehensively consider the time constant of the electromechanical transient process of the doubly fed wind turbine and the sampling period of the control system to ensure that the system fully responds to the compensation current. Calculate the inhibition rate, where is the amplitude of the subsynchronous component of the air gap magnetic field before the compensation current is injected, The amplitude after injection is calculated using double-precision floating-point arithmetic and multiple checks to ensure that the result error is less than , the calculated inhibition rate is divided into three levels, and a hierarchical control strategy is implemented: First level effect processing: When When the current gain is maintained The control parameters of the feedforward decoupling remain unchanged, maintaining the stable operation of the system. At the same time, the effective control parameters under the current working conditions are stored in the historical database to provide a reference for rapid control under similar working conditions in the future. Secondary effect processing: When , for the gain coefficient Perform dynamic adjustment and recalculate the rotor compensation current command and inject new compensation current through S400; Three-level effect processing: When , a 2-fold frequency auxiliary signal is added to the original compensation current, that is, The auxiliary signal amplitude is set to 30%-50% of the current compensation current amplitude, and the phase is synchronized with the subsynchronous oscillation signal through a phase-locked loop to enhance the ability to suppress complex subsynchronous oscillations.

[0026] In summary, this embodiment describes in detail the complete implementation process of a method for suppressing subsynchronous oscillations in a doubly fed grid-connected system. The method accurately obtains the key parameters of subsynchronous oscillations through air gap magnetic field monitoring and feature extraction, generates rotor compensation current instructions based on this, and forms a reverse magnetic field to suppress oscillations from the electromagnetic essence level. The dynamic gain adjustment mechanism ensures that the compensation intensity matches the actual operating conditions. The current injection and feedforward decoupling links ensure the accurate injection of the compensation current. The suppression verification and strategy switching realize the dynamic optimization of the control strategy. The various steps are closely linked to form a complete system of monitoring, calculation, execution, and feedback. The method realizes active suppression of subsynchronous oscillations from the electromagnetic essence level, has adaptive adjustment capabilities, can effectively cope with complex and changeable grid operating conditions, improves the stability and safety of the doubly fed grid-connected system, and provides a strong guarantee for the safe and reliable operation of the doubly fed wind turbine.

[0027] Example 2 like Figure 1As shown, this embodiment provides a method for suppressing subsynchronous oscillations in a doubly-fed grid-connected system. The specific steps of the process are as follows: (1) Air gap magnetic field monitoring and feature extraction A three-axis 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 group of sensors contains three mutually perpendicular Hall elements of X, Y, and Z, which synchronously collect the vector components of the air gap magnetic field in three-dimensional space at a sampling frequency of 20kHz.

[0028] The collected original magnetic field signal is input into a bandpass filter to filter out the power frequency and its harmonic interference and high-frequency mechanical vibration noise, and obtain a pure subsynchronous frequency band magnetic field signal.

[0029] The filtered signal is subjected to fast Fourier transform to convert the time domain signal into a frequency domain spectrum. The frequency component with the largest amplitude is searched in the 5-45 Hz frequency band, which is determined to be the dominant frequency of the subsynchronous oscillation, and the amplitude and phase angle corresponding to this frequency are extracted.

[0030] Redundancy checking and exception handling are performed on the magnetic field signals collected by the sensor: three sets of subsynchronous 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.

[0031] (2) Rotor compensation current command generation According to the amplitude, phase angle and dynamic gain coefficient of the subsynchronous frequency component and 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 side compensation current command.

[0032] The compensation current function introduces a phase shift so that the generated compensation current is in anti-phase with the subsynchronous component of the air gap magnetic field, thereby generating an opposite magnetic field on the rotor side to offset the subsynchronous oscillation of the air gap magnetic field.

[0033] (3) Dynamic gain adjustment During the initial operation of the system, the gain is set to 1.2 so that when the system starts and a sudden oscillation occurs, the compensation current can be quickly provided to respond to the need to suppress subsynchronous oscillations.

[0034] During system operation, the gain is dynamically adjusted according to the suppression rate of the suppression verification and strategy switching feedback and the set target magnetic field amplitude to generate a new gain coefficient, which is then passed to the rotor compensation current command generation link for command generation in the next control cycle.

[0035] Set gain limit protection. When the calculated new gain is greater than the upper limit of 2.0 or less than the lower limit of 0.5, it is forcibly assigned to the upper or lower limit, respectively, to ensure that the rotor-side compensation current is within a safe and controllable range.

[0036] (4) Current injection and feedforward decoupling The generated rotor compensation current command is converted from the stationary coordinate system to the rotor rotating dq coordinate system, decomposed into d-axis and q-axis compensation current components, and added to the current loop reference value of the rotor-side converter to control the rotor-side converter to output the corresponding compensation current.

[0037] The feedforward decoupling voltage is calculated and injected to eliminate the coupling effect between the d-axis and q-axis currents and avoid the compensation current injection affecting the stability of the original vector control.

[0038] (5) Suppressing verification and policy switching After 200ms of compensation current injection, the amplitude of the subsynchronous component of the air gap magnetic field is remeasured using the air gap magnetic field sensor array to calculate the suppression rate.

[0039] (6) Implement hierarchical control strategy based on inhibition rate: If the suppression rate is ≥85%, the current gain and feedforward decoupling control parameters are maintained unchanged to keep the system running stably, and the effective control parameters under the current working conditions are stored in the historical database.

[0040] 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.

[0041] If the suppression rate is less than 60%, a 2-fold frequency auxiliary signal is added to the original compensation current, and the amplitude of the auxiliary signal is set to 30%-50% of the current compensation current amplitude.

[0042] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system, characterized in that: The specific steps of this method are: S100, air gap magnetic field monitoring and feature extraction: A three-axis Hall sensor array is used to collect air gap magnetic field signals in real time. The collected signals are bandpass filtered and spectrum analyzed to extract the amplitude of the subsynchronous frequency component. and phase angle And perform signal redundancy check and exception processing; S200, rotor compensation current command generation: according to the amplitude of the subsynchronous frequency component , phase angle And the dynamic gain coefficient provided by S300 , based on the magnetomotive force balance, establish the compensation current function and generate the rotor side compensation current instruction ; S300, dynamic gain adjustment: When the system is initially running, the gain Set to , provide compensation current when the system starts and when sudden oscillation occurs. During system operation, according to the suppression rate of S500 feedback As well as the target magnetic field amplitude, the gain Dynamically adjust to generate new gain coefficients , and Passed to S200 for command generation for the next control cycle; S400, current injection and feedforward decoupling: the compensation current instruction Convert it into a control signal and inject it into the system, superimpose it on the rotor-side converter current loop reference value, calculate the feedforward decoupling voltage to eliminate the dq axis current coupling, and compensate for subsynchronous oscillation; S500, suppression verification and strategy switching: After 200ms of compensation current injection, the air gap magnetic field sensor array is used again to measure the amplitude of the subsynchronous component of the air gap magnetic field and calculate the suppression rate. , a hierarchical control strategy is executed according to the inhibition rate.

2. The method for suppressing subsynchronous oscillation of 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 three-axis 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 group of sensors contains three mutually perpendicular Hall elements of X, Y, and Z, which are used to synchronously collect the vector components of the air gap magnetic field in three-dimensional space. The sampling frequency of the Hall sensor is set to 20kHz, and the collected original magnetic field signal is input into the bandpass filter to output a pure subsynchronous frequency band magnetic field signal. The filtered signal is subjected to 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 in the spectrum and defined as the subsynchronous oscillation dominant frequency. , and extract the amplitude corresponding to the frequency and phase angle ,in, represents the intensity of the subsynchronous frequency component in the air gap magnetic field, Indicates the phase information of this component.

3. The method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system according to claim 2, characterized in that: In the S100 air gap magnetic field monitoring and feature extraction, the execution logic of signal redundancy check and exception handling is as follows: For the magnetic field signal collected by the sensor, obtain three sets of sub-synchronous characteristic parameters 、 , , 、 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 failure and signal abnormality, 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 judgment, but the amplitude consistency error of the three sets of data is ≥5%, the three sets of data are weighted and the weights are dynamically allocated according to the size of the data deviation, that is, the weight coefficient ,in, For the Deviation of group data from the mean, final amplitude , the final phase .

4. The method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system according to claim 1, characterized in that: In the S200 rotor compensation current command generation, the expression of the compensation current function is: ,in, is the dynamic gain coefficient, which is used to adjust the compensation current. is the mutual inductance coefficient between the stator and rotor, which is used to reflect the degree of electromagnetic coupling between the stator and rotor, and convert the air gap magnetic field strength into the corresponding current instruction size. is the subsynchronous oscillation frequency, is the time variable, By introducing The phase shift makes the generated compensation current anti-phase with the subsynchronous component of the air gap magnetic field, which is used to generate a reverse magnetic field on the rotor side to offset the subsynchronous oscillation of the air gap magnetic field and suppress the subsynchronous oscillation.

5. The method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system according to claim 1, characterized in that: In the S300 dynamic gain adjustment, the gain The dynamic adjustment is based on Update, where is the updated gain coefficient, is the gain coefficient before updating, is the amplitude of the subsynchronous component of the air gap magnetic field currently measured, It is the power frequency magnetic flux density under rated working conditions of the fan, indicating the magnetic field strength of the motor when it is running stably. The target magnetic field amplitude is used to suppress the subsynchronous magnetic field component to 0.5% of the power frequency magnetic density, and set the gain limit protection and the upper and lower gain limits: , , when the calculated When forced to Assigned to ,when When , the value is .

6. The method for suppressing subsynchronous oscillation of a doubly-fed grid-connected system according to claim 1, characterized in that: The S400 current injection and feedforward decoupling are used to convert the rotor compensation current command generated by S200 into Convert from the stationary coordinate system to the rotor rotating dq coordinate system, and decompose the current instruction in the stationary coordinate system into two mutually perpendicular d-axis and q-axis compensation current components in the dq coordinate system. , and add it to the current loop reference value of the rotor-side converter 、 , used to control the rotor-side converter to output the corresponding compensation current, and at the same time, by calculating and injecting the feedforward decoupling voltage ,in, 、 are the feedforward decoupling voltages of the d-axis and q-axis respectively, is the slip angular velocity, which indicates the difference between the motor speed and the synchronous speed. is the magnetic leakage coefficient of the motor, which indicates the degree of magnetic leakage of the motor. is the rotor inductance, 、 are the compensation current components converted to the dq coordinate system respectively.

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

8. The method for suppressing subsynchronous oscillation of 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 specifically as follows: First level effect processing: When When the current gain is maintained The control parameters of the feedforward decoupling remain unchanged to maintain the stable operation of the system. At the same time, the effective control parameters under the current working conditions are stored in the historical database; Secondary effect processing: When , for the gain coefficient Perform dynamic adjustment and recalculate the rotor compensation current command and inject new compensation current through S400; Three-level effect processing: When , a 2-fold frequency auxiliary signal is added to the original compensation current, that is, Frequency component, the auxiliary signal amplitude is set to 30%-50% of the current compensation current amplitude.

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