Subsynchronous oscillation suppression method and system for flexible HVDC transmission system of wind farm

Abstract

The application discloses a method for suppressing subsynchronous oscillation of a flexible DC power transmission system of a wind farm, comprising the following steps: obtaining data information of the flexible DC power transmission system of a target wind farm; calculating voltage and current data information of d-axis and q-axis of the flexible DC power transmission system of the target wind farm; calculating a temporary value of a compensated virtual voltage component of d-axis and q-axis of the flexible DC power transmission system of the target wind farm and performing amplitude limiting processing to obtain a final value of the compensated virtual voltage of d-axis and q-axis of the flexible DC power transmission system of the target wind farm; calculating d-axis and q-axis components of an output voltage reference value of the flexible DC power transmission system of the target wind farm; performing coordinate inverse transformation on the obtained data information and performing corresponding control to complete the suppression of the subsynchronous oscillation of the flexible DC power transmission system of the target wind farm. The application further discloses a system for implementing the method for suppressing subsynchronous oscillation of the flexible DC power transmission system of the wind farm. The application not only realizes the suppression of the subsynchronous oscillation of the flexible DC power transmission system of the wind farm, but also has higher reliability, better accuracy and lower cost.

Description

Technical Field

[0001] This invention belongs to the field of electrical automation, and specifically relates to a method and system for suppressing subsynchronous oscillations in flexible DC transmission systems for wind farms. Background Technology

[0002] With economic and technological development and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and daily life, bringing endless convenience. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] Currently, an increasing number of wind power systems are being integrated into the power grid and generating electricity; therefore, ensuring the absorption of electricity from wind farms has become a crucial task for the power system. Modular multilevel converter-based high-voltage direct current (MMC-HVDC) technology has become one of the effective technical solutions for transmitting wind power. However, both wind farms and MMC-HVDC systems rely on power electronic equipment for grid connection, and the interaction between them may pose a risk of subsynchronous oscillations, which could seriously affect the safe and stable operation of the power system.

[0004] Currently, the main suppression schemes for this type of subsynchronous oscillation include additional equipment schemes and control parameter optimization schemes. While additional equipment schemes have been extensively studied in suppressing subsynchronous / supersynchronous oscillations, they are costly. Control parameter optimization schemes do not alter the original control structure; they only improve the system's local damping characteristics by adjusting the converter station's control parameters, without involving additional hardware investment, making them more suitable for upgrading existing power plants. However, excessively tuning control parameters with the goal of eliminating or weakening the negative damping characteristics of equipment often makes it difficult to coordinate dynamic performance such as wind farm power command tracking and low-voltage fault ride-through. Furthermore, in practical engineering, factors such as pre-tuned original control parameters, the ability to adjust only offline, and limited adjustable range all limit the optimization effect of this type of scheme, resulting in relatively low reliability and accuracy. Summary of the Invention

[0005] One of the objectives of this invention is to provide a highly reliable, accurate, and low-cost method for suppressing subsynchronous oscillations in flexible DC transmission systems for wind farms.

[0006] The second objective of this invention is to provide a system for implementing the subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms.

[0007] The subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms provided by this invention includes the following steps:

[0008] S1. Obtain data information about the flexible DC transmission system of the target wind farm;

[0009] S2. Based on the data obtained in step S1, and using Park coordinate transformation, calculate the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis.

[0010] S3. Based on the data obtained in step S2, and using the phase compensation scheme, calculate the temporary values ​​of the virtual voltage components of the flexible DC transmission system of the target wind farm after compensation for the d-axis and q-axis.

[0011] S4. Perform amplitude limiting processing on the data information obtained in step S3 to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation;

[0012] S5. Based on the data obtained in step S4, calculate the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm;

[0013] S6. Perform coordinate inverse transformation on the data information obtained in step S5 to obtain the three-phase voltage reference value of the flexible DC transmission system of the target wind farm and perform corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm.

[0014] Step S1, which involves acquiring data information about the flexible DC transmission system of the target wind farm, specifically includes the following steps:

[0015] The acquired data information of the flexible DC transmission system of the target wind farm includes the instantaneous A-phase current on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous current and C-phase instantaneous current The instantaneous voltage of phase A on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous voltage and C-phase instantaneous voltage And the phase-locked loop output phase value of the flexible DC converter station in the flexible DC transmission system of the target wind farm. .

[0016] Step S2, which involves calculating the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis based on the data obtained in step S1 and using Park coordinate transformation, specifically includes the following steps:

[0017] Based on the data obtained in step S1, and using the Park coordinate transformation, the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis are calculated, and expressed as follows:

[0018] In the formula The d-axis voltage of the flexible DC transmission system of the target wind farm; The q-axis voltage of the flexible DC transmission system of the target wind farm; The d-axis current of the flexible DC transmission system of the target wind farm; Let q be the q-axis current of the flexible DC transmission system of the target wind farm.

[0019] Step S3, which involves calculating the temporary virtual voltage components of the flexible DC transmission system of the target wind farm after compensation based on the data obtained in step S2 and the phase compensation scheme, specifically includes the following steps:

[0020] Based on the phase compensation scheme, the temporary values ​​of the virtual voltage components on the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation are calculated using the following formula:

[0021] In the formula The temporary value of the virtual voltage component on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The temporary value of the q-axis virtual voltage component after compensation for the flexible DC transmission system of the target wind farm; The steady-state component of the set phase compensation parameter; The set gain coefficient; To take the phase angle function; j is the imaginary unit; t represents time t.

[0022] Step S4 involves performing amplitude limiting processing on the data information obtained in step S3 to obtain the final virtual voltage values ​​of the flexible DC transmission system of the target wind farm after compensation on the d-axis and q-axis. Specifically, this includes the following steps:

[0023] The data obtained in step S3 is subjected to amplitude limiting processing using the following formula to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation:

[0024] In the formula The final value of the virtual voltage on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The final value of the q-axis virtual voltage after compensation for the flexible DC transmission system of the target wind farm; The set voltage limit value.

[0025] Step S5, which involves calculating the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm based on the data obtained in step S4, specifically includes the following steps:

[0026] The reference value of AC current for the flexible DC transmission system of the target wind farm is calculated using the following formula:

[0027] In the formula The d-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The q-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop proportionality coefficient of the flexible DC transmission system for the target wind farm; The AC voltage d-axis reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop integral coefficient of the flexible DC transmission system for the target wind farm; The AC voltage q-axis reference value for the flexible DC transmission system of the target wind farm;

[0028] Based on the AC current reference value of the flexible DC transmission system of the target wind farm, the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm are calculated using the following formula:

[0029] In the formula The d-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The q-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The current inner loop proportionality coefficient of the flexible DC transmission system of the target wind farm; The current inner loop integral coefficient of the flexible DC transmission system of the target wind farm; The angular frequency of the power grid; The equivalent inductance on the AC side of the flexible DC converter station in the flexible DC transmission system of the target wind farm.

[0030] Step S6 involves performing an inverse coordinate transformation on the data information obtained in step S5 to obtain the three-phase voltage reference values ​​of the flexible DC transmission system of the target wind farm and performing corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm. Specifically, this includes the following steps:

[0031] The data obtained in step S5 is transformed inversely to represent the following:

[0032] In the formula The reference value for the A-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the B-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the C-phase output voltage of the flexible DC transmission system of the target wind farm;

[0033] According to the obtained , and The system controls the flexible DC transmission system of the target wind farm to suppress the subsynchronous oscillation of the flexible DC transmission system of the target wind farm.

[0034] This invention also provides a system for implementing the subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms, comprising a data acquisition module, a coordinate transformation module, a primary calculation module, a secondary calculation module, a reference calculation module, and an oscillation suppression module; the data acquisition module, coordinate transformation module, primary calculation module, secondary calculation module, reference calculation module, and oscillation suppression module are connected in series; the data acquisition module is used to acquire data information of the flexible DC transmission system of the target wind farm and upload the data information to the coordinate transformation module; the coordinate transformation module is used to calculate the voltage and current data information of the d-axis and q-axis of the flexible DC transmission system of the target wind farm based on the received data information and the acquired data information, and based on the Park coordinate transformation, and upload the data information to the primary calculation module; the primary calculation module is used to calculate the voltage and current data information of the flexible DC transmission system of the target wind farm based on the received data information and the acquired data information, and based on the phase compensation scheme, based on the phase compensation scheme, and based on the acquired data information. The system calculates the temporary values ​​of the compensated virtual voltage components on the d-axis and q-axis of the flexible DC transmission system of the target wind farm and uploads the data to the secondary calculation module. The secondary calculation module performs amplitude limiting on the received data to obtain the final compensated virtual voltage values ​​on the d-axis and q-axis of the flexible DC transmission system of the target wind farm, and uploads the data to the reference calculation module. The reference calculation module calculates the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm based on the received data and uploads the data to the oscillation suppression module. The oscillation suppression module performs inverse coordinate transformation on the received data to obtain the three-phase voltage reference value of the flexible DC transmission system of the target wind farm and performs corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm.

[0035] The method and system for suppressing subsynchronous oscillations in flexible DC transmission systems for wind farms provided by this invention not only achieves suppression of subsynchronous oscillations in flexible DC transmission systems for wind farms by performing dynamic phase compensation on the control process of the flexible DC transmission system for wind farms, but also has higher reliability, better accuracy, and lower cost. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0037] Figure 2 This is a control block diagram of the method of the present invention.

[0038] Figure 3 This is a schematic diagram of the voltage vector change trajectory of the method of the present invention.

[0039] Figure 4 This is a schematic diagram illustrating the subsynchronous oscillation suppression effect of an embodiment of the method of the present invention.

[0040] Figure 5 This is a schematic diagram of the functional modules of the system of the present invention. Detailed Implementation

[0041] like Figure 1 The diagram shown is a flowchart of the method of the present invention: The subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms disclosed in this invention includes the following steps:

[0042] In practice, multiple wind farms first converge to the AC bus via transmission lines, then are stepped up to the 500kV AC transmission line, and finally connected to the flexible DC transmission system for grid connection after being stepped down by a converter transformer. The flexible DC converter station uses constant AC voltage and frequency control (V / F) to maintain the stability of the point of common coupling (PCC). The grid-side converter (GSVSC) control system of the wind turbines adopts dual closed-loop vector control (constant DC voltage and constant reactive power), and phase-locked loop directional LCL filter capacitor voltage;

[0043] S1. Obtain data information about the flexible DC transmission system of the target wind farm; specifically including the following steps:

[0044] The acquired data information of the flexible DC transmission system of the target wind farm includes the instantaneous A-phase current on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous current and C-phase instantaneous current The instantaneous voltage of phase A on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous voltage and C-phase instantaneous voltage And the phase-locked loop output phase value of the flexible DC converter station in the flexible DC transmission system of the target wind farm. ;

[0045] S2. Based on the data obtained in step S1, and using Park coordinate transformation, calculate the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis; specifically including the following steps:

[0046] Since proportional-integral controllers can only achieve steady-state error control of DC quantities, three-phase VSCs are generally used to control AC quantities in a synchronous rotating coordinate system. This requires converting the acquired instantaneous three-phase voltages into DC quantities through Park coordinate transformation.

[0047] Based on the data obtained in step S1, and using the Park coordinate transformation, the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis are calculated, and expressed as follows:

[0048] In the formula The d-axis voltage of the flexible DC transmission system of the target wind farm; The q-axis voltage of the flexible DC transmission system of the target wind farm; The d-axis current of the flexible DC transmission system of the target wind farm; The q-axis current of the flexible DC transmission system of the target wind farm;

[0049] S3. Based on the data obtained in step S2, and using the phase compensation scheme, calculate the temporary virtual voltage components of the flexible DC transmission system of the target wind farm after compensation for the d-axis and q-axis; specifically including the following steps:

[0050] The control block diagram of the present invention is as follows: Figure 2 As shown; Figure 2 The black part represents the existing control module, and the red part represents the control module added by the present invention.

[0051] exist Figure 2 middle, For constant AC voltage controller, , This is the proportionality coefficient. The integral coefficient; It is a current inner loop controller. , This is the proportionality coefficient. The integral coefficient;

[0052] Compensation voltage d-axis component and the q-axis component of the compensation voltage The results are obtained from cross-coupling calculations, corresponding to the real and imaginary parts of the calculation result, respectively; differential coupling calculations can be expressed as... ,in These are phase compensation parameters;

[0053] The trajectory of the voltage complex vector after cross-coupling calculation in the dq coordinate system is as follows: Figure 3 As shown; when When positive, complex vector Compared to Rotate counterclockwise In radians, the initial phase θ of the actual voltage complex vector increases to... Conversely, when When negative, complex vector Compared to Rotate clockwise radians, at which point the initial phase decreases to Based on the principle of the above cross-coupling strategy, virtual phase parameters can be flexibly designed in the control system to meet the requirements for improving the impedance characteristics of the converter.

[0054] In most existing studies, converter station control strategies typically employ fixed control parameters. While parameter optimization methods are easy to implement, their main drawback is that they may reduce the dynamic performance of the system during normal operation, such as affecting the low-voltage ride-through capability of the wind turbine. In practical engineering scenarios, problems such as pre-set original control parameters, the ability to adjust only offline, and limited parameter adjustment range also exist, all of which limit the effectiveness of parameter tuning. Therefore, this invention introduces the AC current phase as a dynamic compensation term in the virtual phase compensation stage, adjusting the phase compensation parameters... Designed for ;

[0055] Based on the phase compensation scheme, the temporary values ​​of the virtual voltage components on the d-axis and q-axis of the flexible DC transmission system of the target wind farm can be directly calculated using the following formula:

[0056] In the formula The temporary value of the virtual voltage component on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The temporary value of the q-axis virtual voltage component after compensation for the flexible DC transmission system of the target wind farm; The steady-state component of the set phase compensation parameter; The set gain coefficient; To take the phase angle function; j is the imaginary unit; t represents time t;

[0057] S4. Perform amplitude limiting processing on the data information obtained in step S3 to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation; specifically including the following steps:

[0058] The subsynchronous oscillation suppression method proposed in this invention belongs to a type of supplementary active damping control strategy. Its function in actual operation is not for power conversion and control; rather, it is used during system faults or high-power disturbances. and There may be large instantaneous values ​​that affect the system's operating characteristics, thus requiring them to be limited.

[0059] Therefore, the data obtained in step S3 is subjected to amplitude limiting processing using the following formula to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation:

[0060] In the formula The final value of the virtual voltage on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The final value of the q-axis virtual voltage after compensation for the flexible DC transmission system of the target wind farm; The voltage limit value is set, and the limit value is generally taken as 2% to 10% of the rated voltage, with 5% recommended.

[0061] S5. Based on the data obtained in step S4, calculate the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm; specifically including the following steps:

[0062] The control equations for the outer voltage loop in the existing flexible DC converter station control system can be expressed as follows:

[0063] The final values ​​of the phase-compensated d-axis and q-axis voltages are input into the control system of the flexible DC converter station, replacing the uncompensated d-axis and q-axis voltages in the outer voltage loop controller. The reference value of the AC current of the flexible DC transmission system of the target wind farm is then calculated using the following formula:

[0064] In the formula The d-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The q-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop proportionality coefficient of the flexible DC transmission system for the target wind farm; The AC voltage d-axis reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop integral coefficient of the flexible DC transmission system for the target wind farm; The AC voltage q-axis reference value for the flexible DC transmission system of the target wind farm;

[0065] Based on the AC current reference value of the flexible DC transmission system of the target wind farm, the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm are calculated using the following formula:

[0066] In the formula The d-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The q-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The current inner loop proportionality coefficient of the flexible DC transmission system of the target wind farm; The current inner loop integral coefficient of the flexible DC transmission system of the target wind farm; The angular frequency of the power grid; The equivalent inductance on the AC side of the flexible DC converter station in the flexible DC transmission system of the target wind farm;

[0067] S6. Perform inverse coordinate transformation on the data obtained in step S5 to obtain the three-phase voltage reference values ​​of the flexible DC transmission system of the target wind farm and perform corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm; specifically including the following steps:

[0068] The data obtained in step S5 is transformed inversely to represent the following:

[0069] In the formula The reference value for the A-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the B-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the C-phase output voltage of the flexible DC transmission system of the target wind farm;

[0070] According to the obtained , and The system controls the flexible DC transmission system of the target wind farm to suppress the subsynchronous oscillation of the flexible DC transmission system of the target wind farm.

[0071] The effects of the present invention will be further illustrated below with reference to an embodiment:

[0072] Electromagnetic transient simulation verification of the subsynchronous oscillation suppression effect of MMC-receiving wind farms was carried out. The simulation results are as follows: Figure 4 As shown in the figure, when the active power generated by the wind farm jumps from 0.5 pu to 0.7 pu, the introduction of AC current phase feedback... Under parameter control, the oscillation suppression process is significantly accelerated, and the resulting overshoot is significantly reduced; when the active power further jumps from 0.7 pu to 1 pu, a fixed parameter is then used. The system becomes unstable due to parameter instability and induces new subsynchronous oscillations, while the phase of the alternating current is introduced. Under parameter control, the system can still maintain a stable active power output. Therefore, the results shown in the figure verify the correctness of the proposed oscillation suppression method and parameter design.

[0073] The solution of this invention can effectively suppress oscillations after the system experiences subsynchronous oscillations. Continuing to employ this strategy can effectively reduce the risk of subsynchronous oscillations. This solution is relatively simple, requiring no additional external hardware circuitry. It only needs to generate a compensation voltage by performing phase compensation on the d-axis and q-axis voltages of the flexible DC converter station, without excessive algorithmic operations, and has the advantage of being easy to implement.

[0074] like Figure 5The diagram shows the functional modules of the system of this invention: The system disclosed in this invention, which implements the subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms, includes a data acquisition module, a coordinate transformation module, a primary calculation module, a secondary calculation module, a reference calculation module, and an oscillation suppression module; these modules are connected in series. The data acquisition module acquires data information of the flexible DC transmission system of the target wind farm and uploads the data information to the coordinate transformation module. The coordinate transformation module calculates the voltage and current data of the flexible DC transmission system of the target wind farm based on the received and acquired data information, using Park coordinate transformation, and uploads the data information to the primary calculation module. The primary calculation module calculates the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis based on the received and acquired data information, using phase transformation. The compensation scheme calculates the temporary values ​​of the compensated virtual voltage components on the d-axis and q-axis of the flexible DC transmission system of the target wind farm, and uploads the data to the secondary calculation module. The secondary calculation module performs amplitude limiting processing on the received data to obtain the final compensated virtual voltage values ​​on the d-axis and q-axis of the flexible DC transmission system of the target wind farm, and uploads the data to the reference calculation module. The reference calculation module calculates the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm based on the received data, and uploads the data to the oscillation suppression module. The oscillation suppression module performs inverse coordinate transformation on the received data to obtain the three-phase voltage reference value of the flexible DC transmission system of the target wind farm and performs corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm.

Claims

1. A method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms, comprising the following steps: S1. Obtain data information about the flexible DC transmission system of the target wind farm; S2. Based on the data obtained in step S1, and using Park coordinate transformation, calculate the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis. S3. Based on the data obtained in step S2, and using the phase compensation scheme, calculate the temporary values ​​of the virtual voltage components of the flexible DC transmission system of the target wind farm after compensation for the d-axis and q-axis. S4. Perform amplitude limiting processing on the data information obtained in step S3 to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation; S5. Based on the data obtained in step S4, calculate the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm; S6. Perform coordinate inverse transformation on the data information obtained in step S5 to obtain the three-phase voltage reference value of the flexible DC transmission system of the target wind farm and perform corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm.

2. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 1, characterized in that... Step S1, which involves acquiring data information about the flexible DC transmission system of the target wind farm, specifically includes the following steps: The acquired data information of the flexible DC transmission system of the target wind farm includes the instantaneous A-phase current on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous current and C-phase instantaneous current The instantaneous voltage of phase A on the AC side of the three-phase converter in the flexible DC transmission system of the target wind farm. Phase B instantaneous voltage and C-phase instantaneous voltage And the phase-locked loop output phase value of the flexible DC converter station in the flexible DC transmission system of the target wind farm. .

3. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 2, characterized in that... Step S2, which involves calculating the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis based on the data obtained in step S1 and using Park coordinate transformation, specifically includes the following steps: Based on the data obtained in step S1, and using the Park coordinate transformation, the voltage and current data of the flexible DC transmission system of the target wind farm along the d-axis and q-axis are calculated, and expressed as follows: In the formula The d-axis voltage of the flexible DC transmission system of the target wind farm; The q-axis voltage of the flexible DC transmission system of the target wind farm; The d-axis current of the flexible DC transmission system of the target wind farm; Let q be the q-axis current of the flexible DC transmission system of the target wind farm.

4. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 3, characterized in that... Step S3, which involves calculating the temporary virtual voltage components of the flexible DC transmission system of the target wind farm after compensation based on the data obtained in step S2 and the phase compensation scheme, specifically includes the following steps: Based on the phase compensation scheme, the temporary values ​​of the virtual voltage components on the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation are calculated using the following formula: In the formula The temporary value of the virtual voltage component on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The temporary value of the q-axis virtual voltage component after compensation for the flexible DC transmission system of the target wind farm; The steady-state component of the set phase compensation parameter; The set gain coefficient; To take the phase angle function; j is the imaginary unit; t represents time t.

5. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 4, characterized in that... Step S4 involves performing amplitude limiting processing on the data information obtained in step S3 to obtain the final virtual voltage values ​​of the flexible DC transmission system of the target wind farm after compensation on the d-axis and q-axis. Specifically, this includes the following steps: The data obtained in step S3 is subjected to amplitude limiting processing using the following formula to obtain the final virtual voltage values ​​of the d-axis and q-axis of the flexible DC transmission system of the target wind farm after compensation: In the formula The final value of the virtual voltage on the d-axis after compensation for the flexible DC transmission system of the target wind farm; The final value of the q-axis virtual voltage after compensation for the flexible DC transmission system of the target wind farm; The set voltage limit value.

6. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 5, characterized in that... Step S5, which involves calculating the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm based on the data obtained in step S4, specifically includes the following steps: The reference value of AC current for the flexible DC transmission system of the target wind farm is calculated using the following formula: In the formula The d-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The q-axis component of the AC current reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop proportionality coefficient of the flexible DC transmission system for the target wind farm; The AC voltage d-axis reference value for the flexible DC transmission system of the target wind farm; The voltage outer loop integral coefficient of the flexible DC transmission system for the target wind farm; The AC voltage q-axis reference value for the flexible DC transmission system of the target wind farm; Based on the AC current reference value of the flexible DC transmission system of the target wind farm, the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm are calculated using the following formula: In the formula The d-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The q-axis component of the output voltage reference value of the flexible DC transmission system of the target wind farm; The current inner loop proportionality coefficient of the flexible DC transmission system of the target wind farm; The current inner loop integral coefficient of the flexible DC transmission system of the target wind farm; The angular frequency of the power grid; The equivalent inductance on the AC side of the flexible DC converter station in the flexible DC transmission system of the target wind farm.

7. The method for suppressing subsynchronous oscillations in a flexible DC transmission system for wind farms according to claim 6, characterized in that... Step S6 involves performing an inverse coordinate transformation on the data information obtained in step S5 to obtain the three-phase voltage reference values ​​of the flexible DC transmission system of the target wind farm and performing corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm. Specifically, this includes the following steps: The data obtained in step S5 is transformed inversely to represent the following: In the formula The reference value for the A-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the B-phase output voltage of the flexible DC transmission system of the target wind farm; The reference value for the C-phase output voltage of the flexible DC transmission system of the target wind farm; According to the obtained , and The system controls the flexible DC transmission system of the target wind farm to suppress the subsynchronous oscillation of the flexible DC transmission system of the target wind farm.

8. A system for implementing the subsynchronous oscillation suppression method for flexible DC transmission systems in wind farms as described in any one of claims 1 to 7, characterized in that... It includes a data acquisition module, a coordinate transformation module, a primary calculation module, a secondary calculation module, a reference calculation module, and an oscillation suppression module; the data acquisition module, coordinate transformation module, primary calculation module, secondary calculation module, reference calculation module, and oscillation suppression module are connected in series; the data acquisition module is used to acquire data information of the flexible DC transmission system of the target wind farm and upload the data information to the coordinate transformation module; The coordinate transformation module is used to calculate the voltage and current data of the flexible DC transmission system of the target wind farm based on the received data and the acquired data, and to upload the data to the primary calculation module. The primary calculation module calculates the temporary values ​​of the compensated d-axis and q-axis virtual voltage components of the flexible DC transmission system of the target wind farm based on the received and obtained data and a phase compensation scheme, and uploads the data to the secondary calculation module. The secondary calculation module performs amplitude limiting processing on the received data to obtain the final compensated d-axis and q-axis virtual voltage values ​​of the flexible DC transmission system of the target wind farm, and uploads the data to the reference calculation module. The reference calculation module calculates the d-axis and q-axis components of the output voltage reference value of the flexible DC transmission system of the target wind farm based on the received and obtained data, and uploads the data to the oscillation suppression module. The oscillation suppression module is used to perform coordinate inverse transformation on the received data information to obtain the three-phase voltage reference value of the flexible DC transmission system of the target wind farm and perform corresponding control to complete the subsynchronous oscillation suppression of the flexible DC transmission system of the target wind farm.

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