A method for analyzing fault characteristics and line protection adaptability of a wind turbine generator system

Abstract

The application discloses a kind of wind generating set fault characteristic and line protection adaptability analysis method, including the following analysis steps: S1, current and voltage at grid-connected point are detected collection;S2, grid fault type is monitored;S3, determine the control target of wind generating set converter in the process of fault ride-through, and calculate the negative sequence current reference value of converter;S4, according to grid-connected point voltage standard unit, determine the current reference value priority principle that current grid fault should follow;S5, based on current current reference value priority principle, the standard unit value of each current reference value is sequentially calculated;S6, after the difference between the positive and negative sequence current reference values calculated and the actual values corresponding thereto respectively, after PI control link, feedforward compensation and coordinate transformation, generate three-phase positive and negative modulation wave, obtain final modulation wave after summation;The application can quickly respond to grid fault or disturbance, and guarantee that grid operation is stable and reliable.

Description

Technical Field

[0001] This invention belongs to the field of wind turbine grid connection technology, specifically relating to a method for analyzing the fault characteristics of wind turbines and the adaptability of line protection. Background Technology

[0002] Wind energy is gaining increasing attention as a sustainable green energy source. Among them, direct-drive permanent magnet wind turbines have advantages such as high efficiency, low noise, and long lifespan because they eliminate the gearbox, which has a high failure rate in doubly-fed wind turbines. As the installed capacity of wind power generation in regional power grids increases, the impact of wind farms on the safe and stable operation of the power grid is becoming more and more apparent. When grid faults or disturbances cause voltage fluctuations at the grid connection point of wind farms, improper response measures by wind turbines will exacerbate grid fluctuations and may even lead to large-scale grid paralysis, resulting in incalculable losses.

[0003] Therefore, in order to solve the above problems, it is necessary to develop a method for analyzing the fault characteristics of wind turbine generator sets and the adaptability of line protection. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for analyzing the fault characteristics and line protection adaptability of wind turbine generator sets, so as to quickly respond to power grid faults or disturbances and ensure the stable and reliable operation of the power grid.

[0005] The objective of this invention is achieved as follows: a method for analyzing the fault characteristics and line protection adaptability of wind turbine generator sets, comprising the following analysis steps:

[0006] S1. Detect and collect current and voltage data at the grid connection point of the direct-drive permanent magnet wind turbine generator set;

[0007] S2. Monitor the types of power grid faults based on the detection data, and determine whether the power grid voltage drops symmetrically or asymmetrically under the current fault type.

[0008] S3. Determine the control target of the wind turbine generator converter during the fault ride-through process and calculate the reference value of the negative sequence current of the converter.

[0009] S4. Based on the per-unit voltage value at the grid connection point, determine the current reference value priority principle that should be followed for the current grid fault, including the active current priority principle and the reactive current priority principle.

[0010] S5. Based on the priority principle of the current current reference value, calculate the per-unit value of each current reference value in sequence.

[0011] S6. After subtracting the calculated positive and negative sequence current reference values ​​from their corresponding actual values, the three-phase positive and negative modulation waves are generated through PI control, feedforward compensation, and coordinate transformation. The final modulation wave of the wind turbine generator converter is obtained by summing the positive and negative modulation waves.

[0012] Furthermore, in step S2, the power grid faults include three-phase short-circuit faults, two-phase short-circuit faults, and single-phase ground faults. Specifically, the determination of whether a three-phase short-circuit fault or a two-phase short-circuit fault has occurred is based on the line voltage at the grid connection point, and the determination of whether a single-phase ground fault has occurred is based on the phase voltage at the grid connection point.

[0013] Furthermore, in step S2, the grid voltage drops symmetrically when a three-phase short-circuit fault occurs, and drops asymmetrically when a two-phase short-circuit fault or a single-phase ground fault occurs.

[0014] Furthermore, the control objectives in step S3 include: ① suppressing grid-connected negative sequence current; ② suppressing reactive power second harmonic oscillation at the grid connection point; ③ suppressing active power second harmonic oscillation at the grid connection point.

[0015] Furthermore, the reference value of the negative sequence current of the converter in the control target ① in step S3 is expressed as: The reference value for the negative sequence current of the converter in control objective ② is expressed as follows: The reference value for the negative sequence current of the converter in control objective ③ is expressed as follows: .

[0016] Furthermore, the selection of the current reference value priority principle in step S4 includes the following principles: ① When the voltage per unit value at the grid connection point is... When the active current priority principle is adopted; ② When the per-unit voltage at the grid connection point drops symmetrically to When the reactive current priority principle is adopted; ③ When the per-unit voltage at the grid connection point drops asymmetrically to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted; ④ When the per-unit value of the grid connection point voltage drops to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted.

[0017] Furthermore, in step S5, under the active current priority principle, the per-unit value order of each current reference value is as follows: ① Obtain the positive sequence active current component according to the outer loop constant voltage control, and limit its amplitude to obtain... Set the positive sequence reactive current reference value. The initial value is 0. Based on the outer loop voltage control, the positive sequence active current reference value is... In the formula: This is a reference value generated by the outer loop voltage control without limiting. For symbolic functions, ① To limit the amplitude; ② Calculate the corresponding values ​​according to the selected control target. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ③ Determine the reference value of positive sequence reactive current based on the residual current capacity of the converter. In the formula: For outer loop power control or directly given an unlimited reactive power reference value.

[0018] Furthermore, in step S5, under the reactive current priority principle, the per-unit value of each current reference value is taken in the following order: ① Set the positive sequence active current reference value. The initial value is 0. Based on grid-connected reactive power requirements, the positive sequence reactive current reference value is... for: In the formula: ① Represents the per-unit voltage value at the grid connection point of the wind farm; ② Calculate the corresponding values ​​according to the selected control objectives. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ③ Determine the reference value of the positive sequence active current based on the residual current capacity of the converter. In the formula: This is used for outer-loop power control or to directly provide an unlimited active power reference value.

[0019] Furthermore, the PI control loop in step S6 adopts dual closed-loop PI control.

[0020] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] (1) By detecting and collecting the current and voltage at the grid connection point of the direct-drive permanent magnet wind turbine generator, the grid fault type can be monitored based on the detection data, which facilitates rapid response to grid faults or disturbances and ensures stable and reliable grid operation.

[0022] (2) By performing positive and negative sequence decomposition on the collected voltage and current data, the positive and negative sequence components under the dq coordinate are obtained, and the angular velocity and phase angle of the positive sequence voltage component are calculated. Then, according to the grid connection standard requirements, the negative sequence current control target and the current limit of the converter, the reference value of the current sequence component is determined. After subtracting the positive and negative sequence current reference values ​​from their corresponding actual values, the three-phase positive and negative modulation waves are generated after passing through the PI control loop, feedforward compensation and coordinate transformation. The final modulation wave of the converter can be obtained by summing them. This can effectively avoid the power oscillation of the wind turbine fed into the grid and ensure the safe operation of the grid. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0025] like Figure 1 As shown, a method for analyzing the fault characteristics and line protection adaptability of wind turbine generator sets includes the following analysis steps:

[0026] S1. Detect and collect the current and voltage at the grid connection point of the direct-drive permanent magnet wind turbine generator set.

[0027] S2. Monitor the types of power grid faults based on the detection data, and determine whether the power grid voltage drops symmetrically or asymmetrically under the current fault type.

[0028] Preferably, in step S2, the power grid faults include three-phase short-circuit faults, two-phase short-circuit faults, and single-phase ground faults. Specifically, the determination of whether a three-phase short-circuit fault or a two-phase short-circuit fault has occurred is based on the line voltage at the grid connection point, and the determination of whether a single-phase ground fault has occurred is based on the phase voltage at the grid connection point.

[0029] Preferably, in step S2, the grid voltage drops symmetrically when a three-phase short-circuit fault occurs, and drops asymmetrically when a two-phase short-circuit fault or a single-phase ground fault occurs.

[0030] S3. Determine the control target of the wind turbine generator converter during the fault ride-through process and calculate the reference value of the negative sequence current of the converter.

[0031] Preferably, the control objectives in step S3 include: ① suppressing grid-connected negative sequence current; ② suppressing reactive power second harmonic oscillation at the grid connection point; ③ suppressing active power second harmonic oscillation at the grid connection point.

[0032] Specifically, when the grid voltage is asymmetrical, the complex power output of the converter is expressed as follows: In the formula: , Decomposing the complex power expression into active and reactive power parts, we have: In the formula: , Active power reactive power The average value, , for The amplitude of the second harmonic oscillation component, , for The amplitude of the second harmonic oscillation component.

[0033] In the dq coordinate system , , , , , The expression is: In the formula: , These represent the components of the grid voltage on the d-axis and q-axis, respectively. , These represent the components of the grid current on the d-axis and q-axis, respectively. , These represent the positive-order components and the negative-order components, respectively.

[0034] In step S3, if the control objective ① is to suppress the negative sequence component of the converter output current, then the reference value for the negative sequence current of the converter is expressed as: In control objective ②, to suppress fluctuations in output reactive power, the following settings are set: , For a given value, ,neglect , and taking into account Then, in the dq coordinate system , , , , , From the expression, the reference value of the negative sequence current of the converter can be expressed as: In control objective ③, to suppress fluctuations in output active power, the following settings are set: , For a given value, ,neglect , and taking into account Then, in the dq coordinate system , , , , , From the expression, the reference value of the negative sequence current of the converter can be expressed as: .

[0035] S4. Based on the per-unit voltage value at the grid connection point, determine the current reference value priority principle that should be followed for the current grid fault, including the active current priority principle and the reactive current priority principle.

[0036] Preferably, the selection of the current reference value in step S4 includes the following principles: ① When the voltage per unit value at the grid connection point is... When the active current priority principle is adopted; ② When the per-unit voltage at the grid connection point drops symmetrically to When the reactive current priority principle is adopted; ③ When the per-unit voltage at the grid connection point drops asymmetrically to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted; ④ When the per-unit value of the grid connection point voltage drops to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted.

[0037] S5. Based on the priority principle of the current reference value, calculate the per-unit value of each current reference value in sequence.

[0038] Preferably, in step S5, under the active current priority principle, the per-unit value of each current reference value is taken in the following order: ① Obtain the positive sequence active current component according to the outer loop constant voltage control, and limit its amplitude to obtain... Set the positive sequence reactive current reference value. The initial value is 0. Based on the outer loop voltage control, the positive sequence active current reference value is... In the formula: This is a reference value generated by the outer loop voltage control without limiting. For symbolic functions, ① To limit the amplitude; ② Calculate the corresponding values ​​according to the selected control target. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ③ Determine the reference value of positive sequence reactive current based on the residual current capacity of the converter. In the formula: For outer loop power control or directly given an unlimited reactive power reference value.

[0039] Preferably, in step S5, under the reactive current priority principle, the per-unit value of each current reference value is taken in the following order: ① Set the positive sequence active current reference value. The initial value is 0. Based on grid-connected reactive power requirements, the positive sequence reactive current reference value is... for: In the formula: ① Represents the per-unit voltage value at the grid connection point of the wind farm; ② Calculate the corresponding values ​​according to the selected control objectives. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ③ Determine the reference value of the positive sequence active current based on the residual current capacity of the converter. In the formula: This is used for outer-loop power control or to directly provide an unlimited active power reference value.

[0040] S6. After subtracting the calculated positive and negative sequence current reference values ​​from their corresponding actual values, and then passing them through a PI control loop, feedforward compensation, and coordinate transformation, a three-phase positive and negative modulation wave is generated. , The final modulation wave of the wind turbine generator converter is obtained by summing the positive and negative modulation waves.

[0041] Preferably, the PI control stage in step S6 adopts dual closed-loop PI control.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for analyzing the fault characteristics and line protection adaptability of wind turbine generator sets, characterized in that: The analysis includes the following steps: S1. Detect and collect current and voltage data at the grid connection point of the direct-drive permanent magnet wind turbine generator set; S2. Monitor the types of power grid faults based on the detection data, and determine whether the power grid voltage drops symmetrically or asymmetrically under the current fault type. S3. Determine the control target of the wind turbine generator converter during the fault ride-through process and calculate the reference value of the negative sequence current of the converter. S4. Based on the per-unit voltage value at the grid connection point, determine the current reference value priority principle that should be followed for the current grid fault, including the active current priority principle and the reactive current priority principle. S5. Based on the priority principle of the current current reference value, calculate the per-unit value of each current reference value in sequence. S6. After subtracting the calculated positive and negative sequence current reference values ​​from their corresponding actual values, the three-phase positive and negative modulation waves are generated through PI control, feedforward compensation, and coordinate transformation. The final modulation wave of the wind turbine generator converter is obtained by summing the positive and negative modulation waves.

2. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: In step S2, the power grid faults include three-phase short-circuit faults, two-phase short-circuit faults, and single-phase ground faults. Specifically, the determination of whether a three-phase short-circuit fault or a two-phase short-circuit fault has occurred is based on the line voltage at the grid connection point, and the determination of whether a single-phase ground fault has occurred is based on the phase voltage at the grid connection point.

3. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: In step S2, the grid voltage drops symmetrically when a three-phase short-circuit fault occurs, and drops asymmetrically when a two-phase short-circuit fault or a single-phase ground fault occurs.

4. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: The control objectives in step S3 include: ① suppressing grid-connected negative sequence current; ② suppressing reactive power second harmonic oscillation at the grid connection point; ③ suppressing active power second harmonic oscillation at the grid connection point.

5. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 4, characterized in that: The reference value of the negative sequence current of the converter in control target ① in step S3 is expressed as follows: The reference value for the negative sequence current of the converter in control objective ② is expressed as follows: The reference value for the negative sequence current of the converter in control objective ③ is expressed as follows: .

6. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: The selection of the current reference value priority principle in step S4 includes the following principles: ① When the voltage per unit value at the grid connection point is... When the active current priority principle is adopted; ② When the per-unit voltage at the grid connection point drops symmetrically to When the reactive current priority principle is adopted; ③ When the per-unit voltage at the grid connection point drops asymmetrically to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted; ④ When the per-unit value of the grid connection point voltage drops to When a load shedding circuit is connected in parallel on the DC side, the reactive current priority principle shall be adopted.

7. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: In step S5, under the active current priority principle, the per-unit value order of each current reference value is as follows: ① Obtain the positive sequence active current component according to the outer loop constant voltage control, and limit its amplitude to obtain... ; Set positive sequence reactive current reference value The initial value is 0. Based on the outer loop voltage control, the positive sequence active current reference value is... In the formula: This is a reference value generated by the outer loop voltage control without limiting. For symbolic functions, ① To limit the amplitude; ② Calculate the corresponding values ​​according to the selected control target. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ; ③ Determine the reference value of positive sequence reactive current based on the residual current capacity of the converter. In the formula: For outer loop power control or directly given an unlimited reactive power reference value.

8. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: In step S5, under the reactive current priority principle, the per-unit value of each current reference value is taken in the following order: ① Set the positive sequence active current reference value. The initial value is 0. Based on grid-connected reactive power requirements, the positive sequence reactive current reference value is... for: In the formula: ① Represents the per-unit voltage value at the grid connection point of the wind farm; ② Calculate the corresponding values ​​according to the selected control objectives. , And by limiting the current, a new negative sequence current reference value is obtained: , In the formula: ; ③ Determine the reference value of the positive sequence active current based on the residual current capacity of the converter. In the formula: This is used for outer-loop power control or to directly provide an unlimited active power reference value.

9. The method for analyzing the fault characteristics and line protection adaptability of a wind turbine generator set according to claim 1, characterized in that: In step S6, the PI control loop adopts dual closed-loop PI control.

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