Multi-source coordinated current phase regulation based wind power grid-connected distance protection method and system

Abstract

This invention discloses a multi-source coordinated current phase regulation method and system for wind power grid-connected distance protection, belonging to the field of power system relay protection technology. It includes: a fault type identification strategy based on sequence voltage phase characteristics to distinguish between single-phase grounding faults, phase-to-phase faults, and two-phase grounding faults; a remote grid phase reconstruction method based on negative sequence voltage inverse inference to quickly obtain the phase angle of the remote negative sequence current; and a unified phase angle optimization framework to establish an analytical mapping relationship between the positive sequence current phase angle of the wind farm and the phase angle of the remote negative sequence current, wherein a same-phase control strategy is used for single-phase grounding faults, and an anti-phase control strategy is used for phase-to-phase faults. This invention effectively solves the technical problem of traditional distance protection failure caused by converter-type wind farms, reducing the apparent reactance measurement error from 15%-25% to less than 2%, and improving the reliability of zone one protection from 65%-75% to 98.5%. It exhibits excellent robustness and scalability under weak grid conditions and various fault types.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology. Specifically, it relates to a wind power grid-connected distance protection method and system based on multi-source coordinated current phase adjustment, which is particularly suitable for improving the reliability of transmission line distance protection in high-penetration converter-type renewable energy grid-connected scenarios. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the accelerated global energy transition, wind power installed capacity continues to grow, and the penetration rate of wind farms in power transmission systems is constantly increasing. Unlike traditional synchronous generators, wind turbine generators (WTGs) connect to the grid through power electronic converter interfaces, becoming an important part of the modern power grid, but at the same time fundamentally changing the traditional fault current characteristics. Due to the limitations of semiconductor device ratings, converter-interfaced renewable energy (CIRES) has a limited short-circuit current (typically 1.0-2.0 per unit), while the short-circuit current of synchronous generators can reach 5-10 per unit. The converter control system actively adjusts the current amplitude and phase to meet grid regulations such as low-voltage ride-through, resulting in time-varying impedance characteristics during faults.

[0004] Distance protection remains a primary protection solution for transmission systems due to its minimal communication requirements and high reliability. However, traditional distance relays designed for synchronous generator-dominated grids may become unreliable or lose selectivity when applied to converter-interfaced renewable energy grids with high penetration rates. The unconventional fault behavior of converter-interfaced renewable energy sources undermines the fundamental assumption that measured impedance accurately reflects the electrical distance of the fault, potentially leading to increased clearing time, reduced selectivity, or protection maloperation / failure to operate.

[0005] The existing technical solutions mainly have the following technical problems: (1) Limitations of the adaptive impedance compensation method: Existing technology calculates the equivalent impedance of the wind farm in real time and adjusts the relay setting. However, this method requires frequent adjustments and is difficult to adapt to rapid fluctuations in wind power output. More importantly, it is designed for a single fault type and lacks versatility.

[0006] (2) Scalability bottleneck of centralized coordinated protection: Existing technologies use a centralized coordinated controller to collect information from each wind farm and centrally calculate the optimal control strategy, but its computational complexity is O(n^2). 3 It can only handle 3-5 wind farms, has poor scalability, and is highly dependent on communication reliability.

[0007] (3) Incompleteness of single fault type control strategy: Existing technologies design specific current control strategies for single-phase ground faults or phase-to-phase faults respectively, lack a unified processing framework, and do not fully consider the impact of zero-sequence current on the judgment of protection zone in two-phase ground faults.

[0008] (4) Insufficient robustness under weak grid conditions: Under weak grid conditions with low short-circuit ratio (SCR), the apparent impedance measurement error of traditional distance protection can exceed 20%, and the protection reliability is reduced from 85-90% in normal grid to 65-75%.

[0009] (5) Lack of handling two-phase grounding faults: Existing methods lack effective measures to deal with the zero-sequence current coupling effect of two-phase grounding faults such as ABG, BCG, and CAG, resulting in inherent phase deviations in the compensation coefficients and affecting the accuracy of protection zone judgment.

[0010] In summary, existing technologies are insufficient to simultaneously meet the comprehensive requirements of large-scale wind power grid-connected systems in terms of protection accuracy, fault type coverage, scalability, and robustness, necessitating a new coordinated control method. Summary of the Invention

[0011] The technical problem this invention aims to solve is: how to design a distance protection method that can achieve high precision, high reliability, and strong robustness in large-scale wind power grid-connected systems, while also possessing good scalability and real-time performance. Specifically, it includes: (1) How to establish a unified phase angle control framework applicable to single-phase ground fault (AG), phase-to-phase fault (AB) and two-phase ground fault (ABG) to cover more than 90% of asymmetrical fault types in power systems; (2) How to reduce the apparent reactance measurement error from 15%-25% in the traditional method to less than 2%, and improve the reliability of Zone 1 protection from 65%-75% to more than 98%; (3) How to reduce the computational complexity of multi-wind farm coordinated optimization, from the existing centralized method's O(n) 3 The computation time is reduced to O(n), supporting collaborative optimization of 10-15 wind farms; (4) How to maintain stable protection performance and achieve strong robustness under weak grid conditions (SCR=1.3) and different power factors (0.8-1.0).

[0012] To address the aforementioned technical problems, this invention provides a distance protection method and system for wind power grid-connected systems based on multi-source coordinated current phase regulation, comprising the following technical solutions: Technical Solution 1: Unified Phase Angle Control Framework A unified phase angle control framework is provided to eliminate distance protection measurement errors caused by converter-type wind farms. Its key feature is that by establishing a precise phase angle relationship between the positive-sequence current of the wind farm and the negative-sequence current at the far end, the imaginary part of the additional impedance in the apparent impedance measured by the relay during asymmetrical faults approaches zero. Specifically, it includes: (1) Single-phase ground fault in-phase control strategy: When AG (phase A ground), BG (phase B ground), or CG (phase C ground) faults occur, the phase angle of the positive sequence current in the wind farm is set to be equal to the phase angle of the negative sequence current at the far end. ; By configuring the positive-sequence current and the negative-sequence current in phase, the compensation coefficient M of the grounding impedance relay measurement is adjusted. ag The phase angle approaches zero, thus achieving decoupling of the imaginary part of the influence of grounding resistance.

[0013] (2) Phase-to-phase fault reverse control strategy: When AB, BC, or CA faults occur, the phase angle of the positive sequence current of the non-faulted phase is set to differ from the phase angle of the negative sequence current at the far end by 180 degrees. ; By utilizing the inherent anti-phase characteristics of positive and negative sequence currents during phase-to-phase faults, the compensation coefficient M measured by the phase-to-phase impedance relay is adjusted. ab The phase angle is zero.

[0014] (3) Rotational compensation strategy for two-phase ground fault protection zone: When ABG (AB phase ground), BCG (BC phase ground), or CAG (CA phase ground) faults occur, the same reverse-phase control as for inter-phase faults is adopted, and the protection zone of the circular impedance characteristic (Mho type) distance relay is rotated 14 degrees clockwise: θ rot = 14°; The rotation angle is based on the half-angle compensation principle, which symmetrically distributes the maximum 28-degree phase deviation caused by zero-sequence current coupling, reducing the maximum error on one side to 14 degrees.

[0015] Technical Solution 2: Remote Negative Sequence Current Phase Reverse Inference Method A method for inferring the phase of a remote negative-sequence current is provided to quickly acquire the phase information of the negative-sequence current on the remote power grid side without the need for remote communication. The method is characterized by using local measurements from a distance protection relay and line parameters for reverse calculation. Specifically, it includes: (1) Phase inference based on negative sequence voltage: using the negative sequence voltage measured at the relay terminal and line negative sequence impedance Z SL2 The phase angle of the negative sequence current at the far end is calculated in reverse by using the impedance voltage drop: ; (2) Fast response characteristics: This reverse inference method avoids remote communication delay and shortens the response time to 5-10ms, which meets the fast response requirements of relay protection.

[0016] Technical Solution 3: Phase Angle Reverse Mapping Current Reference Value Generation Method A method for generating a phase angle reverse mapping current reference value is disclosed, used to quickly convert a target phase angle into a converter dq-axis current reference value. Its key feature is the use of an analytical reverse-mapping algorithm to avoid the delay accumulation of traditional PI controllers. Specifically, it includes: (1) Formula for inverse calculation of dq-axis current: Based on the phase angle of the target positive sequence current The reference value of reactive current I for low voltage ride-through requirements 1qref Calculate the reference value for the direct-axis current: ; Where θ 1v This is the positive sequence voltage phase angle detected by the phase-locked loop.

[0017] (2) Equal-phase proportional normalization limiting: When the total amplitude of the current reference value exceeds the converter capacity limit I max When using a normalization factor The d-axis and q-axis currents are scaled synchronously and proportionally to ensure that the phase angle remains strictly unchanged after limiting, with a phase angle error of less than 2.5%.

[0018] Technical Solution 4: Distributed Consistency Multi-Wind Farm Coordination and Optimization Mechanism A distributed consensus multi-wind farm coordination optimization mechanism is proposed for phase angle collaborative optimization when multiple wind farms are connected to the grid. Its key feature is the use of a distributed consensus algorithm combined with local gradient optimization to achieve rapid convergence. Specifically, it includes: (1) Neighborhood coordination network construction: Each wind farm forms a communication graph G=(V,E). When the electrical distance between two wind farms is less than a preset threshold, a neighborhood relationship is established.

[0019] (2) Hybrid iterative update strategy: Each wind farm updates according to the synchronization period T coord Phase angle is updated every 10ms. ,in =0.1-0.2 is the consistency step size. =0.01-0.1 represents the local optimization weight.

[0020] (3) Factors affecting weight allocation: weight The allocation is based on the proportion of fault current amplitude of each wind farm, with priority given to optimizing wind farms that contribute the most current.

[0021] (4) Fast convergence: The algorithm converges to the global optimum within 5-10 iterations (50-100ms), with a computational complexity of O(n).

[0022] (5) Communication fault tolerance mechanism: Set communication timeout threshold T timeout =100ms, automatically switch to local control mode when communication is interrupted to ensure that a single point of failure does not affect the overall system performance.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Unified technical framework: Establish a unified phase angle mathematical relationship applicable to three types of asymmetrical faults: AG, AB, and ABG, covering more than 90% of fault types in power systems, and solving the problem that existing technologies lack universality for single fault types.

[0024] 2. Superior protection accuracy: Compared with traditional low voltage ride-through control methods, the apparent reactance measurement error is reduced from 15%-25% to less than 2%, with an accuracy improvement of 7-12 times; the reliability of Zone 1 protection is improved from 65%-75% to 98.5%, an improvement of 23-33 percentage points; and the reliability of Zone 2 protection reaches 99.2%.

[0025] 3. Strong robustness: Error <3% under weak power grid conditions (SCR=1.3), compared to >20% with traditional methods; Error fluctuation <1% within the power factor range of 0.8-1.0; Tolerance for ±10% measurement error of line parameters, adaptable to complex power grid environments.

[0026] 4. Excellent scalability: The distributed coordination framework supports collaborative optimization of 10-15 wind farms, which is 3-5 times better than the existing centralized methods limited to 3-5 units. The convergence time is 50-100ms, and the computational complexity is reduced from O(n^2) to O(n^2). 3 The value decreases to O(n).

[0027] 5. Real-time and fast response: Single-cycle control response time is 20-40ms, and the computational cost is <2ms / cycle (existing methods are 5-10ms), meeting the requirement of power system primary equipment protection to operate within 100ms.

[0028] 6. Excellent compatibility: Compliant with IEEE1547 and IEC61400-21 international power grid regulations, it can be implemented through software upgrades on existing Mho type, quadrilateral characteristic, lens type and other distance relays without hardware modification, reducing implementation costs by more than 80%.

[0029] 7. Fast convergence characteristics: The distributed consensus algorithm converges to the global optimum within 5-10 iterations, which is 5-8 times faster than the gradient descent method. The communication fault tolerance mechanism ensures that a single point of failure does not affect the overall system performance.

[0030] The present invention is superior to the prior art in terms of protection accuracy, reliability, fault coverage, adaptability to weak power grids, and multi-source coordination ability, especially having significant advantages in the scenario of high-penetration wind power grid connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In the drawings: FIG. 1 is a schematic diagram of the topology structure of a wind power grid connection system and the configuration of distance protection. The figure shows a typical grid connection topology in which a wind farm WF is connected to an equivalent power source S of the power grid through a step-up transformer and a transmission line L12. A distance protection relay R12 is installed at the outlet bus of the wind farm, and its protection range covers the transmission line L12. In the figure, F represents the grounding fault point on the line, which is located at a distance of p (0 < p < 1) of the total line length from the relay R12. The injected current I. on the wind farm side is also marked in the figure. W , the injected current I. on the grid side S , the measured voltage U. of the relay R , and the measured current I. R and the reference directions of, where the measured current . The protection range of Zone 1 is set to 85% of the line length, and the protection range of Zone 2 is set to 120% of the line length.

[0032] Figure 2 is a schematic diagram of the equivalent circuit principle of a single-phase grounding fault (phase A grounding). In the figure, the symmetric component method is used to decompose the asymmetric fault into three independent networks of positive sequence, negative sequence, and zero sequence, and the three sequence networks are connected in series at the fault point. The positive sequence current on the wind farm side, the positive sequence current on the grid side, the negative sequence current <着 on the grid side, and the zero sequence current are shown in the figure. Z W1 , Z S1 respectively represent the positive sequence equivalent impedances on the wind farm side and the grid side, and Z L1 represents the positive sequence impedance of the line from the fault point to the relay. The grounding impedance R g is located between the fault point and the ground. The generation position of the additional impedance Z is also marked in the figure. This additional impedance is caused by the phase difference between the wind farm current and the grid current and is the root cause of the measurement error of the distance protection.

[0033] Figure 3 is a diagram showing the relationship between the impedance locus and the protection zone under a single-phase grounding fault. In the figure, the horizontal axis represents the resistance R (unit: Ω), the vertical axis represents the reactance X (unit: Ω), and the origin O is the relay installation position. The circular area is the protection zone of Zone 1 of the circular impedance characteristic (Mho type) relay, and the end point of its diameter corresponds to the line end impedance Z LThe figure shows the impedance trajectories in two cases: (1) The dashed trajectory indicates that when using traditional low voltage ride-through control, the measured impedance at 90% of the line length deviates from the protection zone, which may cause the protection to fail to operate; (2) The solid trajectory indicates that after using the phase angle control strategy of the present invention, the measured impedance is stably maintained within the protection zone, and the impedance trajectory extends along the resistance axis (the imaginary part of the additional impedance is zero), which verifies the effectiveness of the method of the present invention.

[0034] Figure 4 A schematic diagram illustrating the technical principle of eliminating the imaginary part of the additional impedance. This diagram uses a layered structure to show the core technical logic of the invention: the first layer (problem layer) points out the fundamental problem of abnormal fault current phase caused by wind farm converter control; the second layer explains that this problem causes the relay-measured apparent impedance to contain the imaginary part of the additional impedance. X; The third layer (analysis layer) reveals that the additional impedance phase angle is determined by the positive sequence current phase angle of the wind farm. Phase angle ∠ with the far-end negative sequence current The difference determines the phase angle control strategy; the fourth layer (strategy layer) displays a unified phase angle control strategy for the three types of faults: AG faults use in-phase control ( ), AB faults are controlled by inverse phase control ( The ABG fault is handled by reverse phase control combined with 14° protection zone rotation compensation; the fifth layer (effect layer) shows that the above strategy makes the imaginary part of the additional impedance approach zero, and finally achieves the technical effect of apparent reactance error <2% and zone one protection reliability 98.5%.

[0035] Figure 5 A flowchart illustrating the implementation of a multi-source coordinated current phase regulation method is provided. The complete control flow is shown: First, the fault type is identified by real-time monitoring of three-phase voltage and current and sequence voltage phase analysis. Then, the corresponding phase angle control strategy is selected based on the fault type (AG fault with equal phase angles, AB fault with a 180-degree phase difference, ABG fault with rotating protection zone). Next, the sequence current is extracted through symmetrical component transformation, the phase angle of the far-end negative sequence current is calculated, and the target positive sequence current phase angle is set. Then, the dq-axis current reference value is calculated, and proportional scaling is performed when it exceeds the converter current limit. For multi-wind farm scenarios, a distributed consensus coordination algorithm is used. Finally, the control signal is output through converter dq-axis decoupling control. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] Where there is no conflict, the embodiments and features described in this application may be combined with each other.

[0040] like Figure 5 As shown, the system of the present invention includes a fault detection module, a phase angle calculation module, a current reference value generation module, a current control module, a distributed coordination module, and a protection zone compensation module. The modules work in coordination to achieve high-precision distance protection for the wind power grid-connected system.

[0041] Example 1: Current Phase Adjustment in Single-Phase Ground Faults This embodiment provides a specific method for adjusting the current phase when a phase-A grounding (AG) fault occurs in transmission line L12.

[0042] System parameter settings: (1) Grid voltage: 120kV (effective value of line voltage); (2) Transmission line length: 200km; (3) Positive sequence impedance: 0.035 + j0.352 Ω / km; (4) Zero-sequence impedance: 0.105 + j1.40 Ω / km; (5) Short-circuit ratio (SCR): 3.0; (6) Wind farm capacity: 10MW (5×2MW units).

[0043] Fault setting: The fault location is at 40% of the line (80km from R12 relay), and the grounding resistance is R. g =5Ω.

[0044] Specific implementation steps: Step 1: Fault Detection By monitoring the three-phase voltage, it was found that the voltage of phase A dropped to 0.42 per unit, while the voltages of phases B and C were basically normal, indicating that the fault was a ground fault in phase A.

[0045] Step 2: Sequence component extraction Symmetrical component transformation is used to extract the positive and negative sequence current components, and the sliding DFT algorithm is used to calculate the positive sequence current of phase A of the wind farm within one period (20ms). and the negative sequence current of phase A on the grid side .

[0046] Step 3: Phase inference of the negative sequence current at the far end Based on the negative sequence voltage measured at relay R12 The phase angle of the far-end negative sequence current is calculated to be -100° using the formula:

[0047] Step 4: Setting the positive sequence current phase angle Based on the in-phase control strategy for single-phase ground faults ∠ =∠ The target phase angle of the positive sequence current of the wind farm is set to -100°.

[0048] Step 5: Calculation of current reference value Given the reactive current reference value I 1qref =0.8 per unit (meets LVRT requirements), phase-locked loop detection voltage phase θ 1v =0°, calculate the d-axis current reference value as I 1dref =0.8 / tan( 100° 0° 90°) = 0.6 per unit value.

[0049] Step 6: Current Limiting Check Total reference current amplitude If the per-unit value is less than 1.2 per-unit value (converter heat capacity limit), no limiting is required.

[0050] Step 7: Converter control execution Precise phase angle adjustment is achieved through dq axis decoupling control, with a control response time of 20-40ms.

[0051] Implementation results: Simulation results show that the positive sequence current phase angle of the wind farm after implementing this method is [value missing]. Phase angle with the negative sequence current on the grid side All converge to -100°, with compensation coefficient M. ag The phase angle is close to 0°, so that the additional impedance contains only the resistive component. The measured apparent reactance is 27.63Ω, the actual line reactance is 28.14Ω, and the error is only 0.51Ω (1.8%). The impedance trajectory is stably maintained within the protection range of Zone 1 (85% of the line length).

[0052] Comparative example: When using traditional fault ride-through control, without phase adjustment, the apparent reactance error reaches 4.5Ω (16%), and the impedance trajectory deviates from the protection zone, which may lead to protection failure or delayed operation.

[0053] Example 2: Current Phase Adjustment for Phase-to-Phase Faults This embodiment provides a current phase adjustment method when an AB phase-to-phase fault occurs in transmission line L12.

[0054] The system parameters are the same as in Example 1, the fault is set at 40% of the line, and the fault resistance R g =5Ω.

[0055] Specific implementation steps: Step 1: Fault Detection A voltage drop was detected in phases A and B, while the voltage in phase C was normal, indicating a fault between phases A and B.

[0056] Step 2: Sequence component extraction Phase-to-phase faults do not generate zero-sequence current; only positive and negative sequence components are extracted: positive sequence current of phase C in a wind farm. and the negative sequence current of phase C on the grid side .

[0057] Step 3: Determine the phase angle relationship Based on the derivation of the AB phase-to-phase fault, the required phase relationship is:

[0058] Step 4: Phase inference of the far-end negative sequence current Utilizing the negative sequence voltage of phase C Sum sequence impedance Z SL2 Calculations yielded .

[0059] Step 5: Setting the positive sequence current phase angle The target phase angle is 80° 180° = 100°.

[0060] Step 6: Current Reference Value Calculation and Control Using the same calculation and control process as in Example 1, I was obtained. 1dref =0.6 per unit value, I 1qref =0.8 per unit value.

[0061] Implementation results: Simulation results show that: phase angle and 180° 100°, perfect match; compensation coefficient M abThe phase angle is close to 0°; the measured apparent reactance is 28.42Ω, the actual line reactance is 28.14Ω, and the error is only 1.0%; under near-end faults (0.5% of line length) and far-end faults (90% of line length), the impedance trajectory remains within the correct protection zone; under weak grid conditions (SCR=1.3) and different pre-fault power factors (0.8-1.0), the protection reliability remains above 95%, verifying the robustness of the method.

[0062] Example 3: Rotating Compensation for Protection Zones in Two-Phase Ground Faults This embodiment provides a rotating compensation method for the protected area of ​​an ABG two-phase ground fault. The system parameters are the same as in Embodiment 1, with the fault location at 40% of the line length.

[0063] Fault setting: Grounding resistance R g =10Ω, interphase resistance R f =5Ω.

[0064] Specific implementation steps: Step 1: Fault Detection A voltage drop was detected in both phases A and B, along with a grounding current (zero-sequence current), indicating a two-phase grounding fault (ABG).

[0065] Step 2: Sequence component extraction Symmetrical component transformation is used to extract positive-sequence, negative-sequence, and zero-sequence current components, and the ratio of zero-sequence to negative-sequence current is analyzed (in this example, the ratio is approximately 0.25, which is less than 0.3).

[0066] Step 3: Determine the phase angle relationship The same anti-phase control strategy as for inter-phase faults is adopted:

[0067] Step 4: Rotation compensation of the protected area Due to the zero-sequence current coupling effect, the compensation coefficient M ag2 There is an inherent phase angle deviation of approximately 28°. To minimize the maximum deviation, a 14° clockwise rotation of the protection zone (half-angle compensation principle) is adopted. This rotation angle is determined based on Monte Carlo simulation statistics within the grounding resistance range of 0-40Ω.

[0068] Step 5: Current Reference Value Calculation and Control Perform the same dq-axis current reference value calculation and converter control process as in Examples 1 and 2.

[0069] Implementation results: Simulation results of the rotation compensation strategy for the protected area show that: ① Without rotational compensation, the inherent phase angle deviation of the compensation coefficient is about 28°, causing the measured impedance to deviate from the protection zone; ② After rotating the 14° protection zone clockwise, the impedance trajectory deviation angle decreased from 28° to less than 3°; ③ The measured apparent reactance is 28.03Ω, while the actual line reactance is 28.14Ω, with a relative error of 0.39%. ④ Zone 1 protection action time is 35ms, and Zone 2 protection reliable action is after a delay of 300ms; ⑤ Under different combinations of grounding resistance (5-50Ω) and phase-to-phase resistance (2-20Ω), the protection reliability reaches over 97%; The effectiveness of the geometric compensation principle (rotation angle is half the phase deviation angle) has been verified.

[0070] Example 4: Phase Control of DFIG Type Wind Turbine This embodiment provides a phase angle control scheme for a doubly-fed induction generator (DFIG) type unit. The DFIG stator is directly connected to the grid, and the stator current phase angle is indirectly controlled through a rotor-side converter. The adjustment capability is limited by the capacity of the rotor-side converter (30% of the rated capacity).

[0071] System parameter settings: The system voltage and line parameters are the same as in Example 1. The DFIG wind farm has a capacity of 10MW (5×2MW units) and the rotor-side converter capacity is 30% of the rated capacity.

[0072] Specific implementation steps: Step 1: Fault Detection and Sequence Component Extraction The same method as in Example 1 was used to detect a phase A ground fault and extract the stator-side positive sequence current. and grid-side negative sequence current .

[0073] Step 2: Establishing the relationship between stator current phase angle and rotor current DFIG stator current phase angle ∠ With rotor current The relationship is: , Where s is the slip ratio, L m L s L r These are mutual inductance, stator inductance, and rotor inductance, respectively.

[0074] Step 3: Target Phase Angle Setting Based on the in-phase control strategy for single-phase ground faults, the target phase angle of the stator positive sequence current is set. .

[0075] The capacity of the DFIG rotor-side converter is limited to 30% of the rated capacity. When the rotor current demand exceeds the limit, the same equal-phase proportional normalization strategy as in Example 1 is used for limiting.

[0076] Step 5: Slip Frequency Compensation Because the DFIG rotor speed is asynchronous, the rotor current frequency is the slip frequency sf. s (where f) s (For the grid frequency), slip compensation needs to be added to the rotor-side control. The slip rate s is usually in the range of -0.3 to +0.3.

[0077] Step 6: Coordination of grid-side converters The grid-side converter is controlled in the same manner as in Example 1, providing partial reactive power support and DC bus voltage stability.

[0078] Implementation results: Simulation results show that after implementing this method, DFIG-type wind farms exhibit the following results: ①The phase angle of the stator positive sequence current converges to -95°, with a deviation from the target value of less than 5°; ②The apparent reactance error is 2.8%, which is slightly higher than that of the full-power converter type (1.8%), but still far better than the 15%-25% of the traditional method; ③ The rotor-side converter current utilization rate reached 85%, which did not exceed the capacity limit; ④ The control response time is 30-50ms, which is slightly slower than the 20-40ms of the full-power converter type, mainly due to the additional delay of stator-rotor coupling; ⑤ The protection reliability remains above 96% under different slip rates (-0.2 to +0.2).

[0079] This embodiment shows that the method of the present invention is applicable to DFIG type wind turbines. It indirectly controls the stator current phase angle through the rotor-side converter. Although the accuracy and response speed are slightly lower than those of the full-power converter type, it can still ensure the reliable operation of the distance protection.

[0080] Example 5: Robustness Verification under Weak Power Grid Conditions This embodiment verifies the protection performance under weak grid conditions (Short-circuit ratio SCR=1.3).

[0081] System parameter modification: By increasing the equivalent grid impedance, the short-circuit ratio is reduced from 3.0 to 1.3, and the positive sequence voltage drops to 0.42 per unit, which is higher than the phase-locked loop operating threshold of 0.1 per unit.

[0082] Fault type: Phase A ground fault, fault location 40% of line length.

[0083] Implementation results: Simulation results show the following performance under weak grid conditions: ① The measured apparent reactance is 27.89Ω, while the actual line reactance is 28.14Ω, with a relative error of 0.89%. ② At different fault locations (0.5%-90% of the line length from the relay), the error range is 0.5%-1.2%, with an average error of 0.78%; ③ Compared with the error of more than 20% in traditional fault ride-through methods under weak power grids, the error of this invention is reduced by more than 95%; ④ The phase-locked loop (PLL) can still operate stably when the voltage drops to 0.1 per unit, with a phase error of less than ±2 degrees; this verifies the phase angle relationship. The theoretical conclusions, which are independent of grid impedance, are highly robust.

[0084] Example 6: Protection reliability verification under different pre-fault power factors This embodiment verifies the protection reliability and robustness under different pre-fault power factor conditions.

[0085] System parameters: Same as in Example 1, wind farm capacity 10MW, transmission line 200km, fault location 40% of line length.

[0086] Power factor setting: By adjusting the active and reactive power output of the wind farm, the power factor before the fault can be set to 0.80, 0.85, 0.90, 0.95 and 1.0 (lagging), respectively, covering the common operating range of wind farms.

[0087] Fault type: Tested using phase A ground fault, grounding resistance R g =10Ω.

[0088] Specific implementation process: (1) Under different power factors, the initial operating state of the wind farm is as follows: Power factor 0.80: active power 8MW, reactive power 6Mvar (lagging); Power factor 0.90: active power 9MW, reactive power 4.36Mvar (lagging); Power factor 0.95: active power 9.5MW, reactive power 3.12Mvar (lagging); Power factor 1.0: active power 10MW, reactive power 0Mvar (pure active power).

[0089] (2) After the fault occurs, phase angle control is performed according to the method of the present invention, and the target phase angle is set to the phase angle of the far-end negative sequence current; (3) Low voltage ride-through control requires injecting reactive power support according to the degree of voltage drop, and I is calculated according to LVRT requirements under all power factors. 1qref ; (4) Calculate I using the dq back-calculation algorithm 1dref And perform a current limiting check.

[0090] Implementation results: Verification results under different pre-fault power factors show: ① Power factor 0.80; apparent reactance error 0.92%; Zone 1 protection reliability 98.2%; ② Power factor 0.85; apparent reactance error 0.85%; Zone 1 protection reliability 98.5%; ③ Power factor 0.90; apparent reactance error 0.78%; Zone 1 protection reliability 98.7%; ④ Power factor 0.95; apparent reactance error 0.71%; Zone 1 protection reliability 98.9%; ⑤ Power factor 1.0: apparent reactance error 0.68%, zone one protection reliability 99.1%; The error fluctuation range across the entire power factor range (0.80-1.0) is only 0.24%, with a standard deviation of 0.09%, demonstrating extremely strong robustness. Under all power factors, the protection action time is within the range of 20-40ms, which meets the fast response requirements of relay protection; Compared with traditional methods, which can have an error of 8%-12% at low power factor (0.80), the error of this invention is reduced by more than 90%.

[0091] Verification Conclusion: This embodiment verifies the adaptability of the method of the present invention to pre-fault operating conditions. The core of the phase angle control strategy is to establish a unified phase relationship between the positive-sequence current of the wind farm and the negative-sequence current at the far end, which is independent of the pre-fault power factor and depends only on the fault type and grid parameters. This characteristic makes the method reliable under a wide range of power factor operating conditions in wind farms, meeting the complex operating requirements of actual power grids.

[0092] Example 7: Multi-source coordinated distributed optimization This embodiment provides a distributed coordination method for three wind farms (each 10MW).

[0093] System configuration: The three wind farms are located at distances of 50km, 120km and 180km from the fault point, respectively, and are connected via the IEC61850 GOOSE communication protocol or fiber optic network.

[0094] Coordination algorithm parameters: Communication synchronization period: 10ms (GPS synchronization); Consistency step size: =0.15; Local optimization weight: Impact weight: allocated according to the proportion of fault current amplitude of each wind farm.

[0095] Specific implementation steps: (1) Initialization: Each wind farm independently calculates the initial target phase angle based on local voltage measurements, resulting in a phase inconsistency of 15°-20°; (2) Distributed iteration: Each wind farm k adjusts its phase angle according to the update formula:

[0096] (3) Convergence criterion: When the phase angle change between two adjacent iterations is less than 0.5°, convergence is considered achieved; (4) Communication fault tolerance: If the communication link fails for more than 100ms, the wind farm will automatically switch to local control mode.

[0097] Implementation results: Simulation results of multi-source coordinated optimization show that: Without coordination, each wind farm is controlled independently, with an apparent reactance error of 8.3% and a phase angle deviation of 12.5°. After adopting distributed consensus coordination, the apparent reactance error was reduced to 2.1%, a reduction of approximately 75%. The phase angle deviation of the three wind farms converged from 12.5° to within 3.2°, improving consistency; The convergence time is 45ms (3 wind farms), and theoretical analysis and simulation verification show that it can be extended to 10-15 wind farms with a convergence time of 60-70ms. The reliability of protection in Zone 1 improved from 87.3% (without coordination) to 98.5%, an increase of 11.2 percentage points. The reliability of Zone 2 protection improved from 92.1% to 99.2%; Communication fault tolerance mechanism test: When the communication link fails, each wind farm automatically switches to local control mode within 100ms, and the protection reliability remains above 90%.

[0098] Based on the verification results of the above embodiments, the method of the present invention is superior to the prior art in terms of protection accuracy, reliability, fault coverage, adaptability to weak power grids, and multi-source coordination capability. As shown in Table 1, the apparent reactance error is reduced to below 2%, the reliability of Zone 1 protection reaches 98.5%, and the reliability of Zone 2 protection reaches 99.2%. Table 1: Comparison of the present invention with existing technologies

[0099] The main technical parameters involved in this invention are shown in the table below: Table 2: Main Technical Parameters

[0100] Application scenarios: This invention is applicable to the following main application scenarios, and provides specific system parameters and expected performance indicators for each scenario: Scenario 1: Grid-connected power transmission system for large-scale wind power bases Application conditions: Multiple wind farms (total capacity 100-500MW) transmit power to the load center through long-distance transmission lines (50-300km), grid short-circuit ratio SCR=2.0-5.0, voltage level 110-220kV.

[0101] System Configuration: Number of wind farms: 3-10, capacity of each farm: 10-50MW; Transmission lines: positive sequence impedance 0.03-0.04+j0.3-0.4Ω / km, zero sequence impedance 0.1-0.15+j1.2-1.6Ω / km; Communication method: Fiber optic communication or IEC 61850 GOOSE, communication latency <10 milliseconds; Relay protection: Circular impedance characteristic (Mho type) distance protection, Zone 1 range 85% of line length, Zone 2 range 120% of line length.

[0102] Expected performance metrics: Apparent reactance measurement error: <2% (15-25% for traditional methods); Zone 1 protection reliability: >98% (65-75% for traditional methods); Zone 2 protection reliability: >99% (traditional methods 80-85%); Control response time: 20-40ms (meets relay protection requirements); Distributed coordination convergence time: 50-100ms; Fault types covered: AG / BG / CG, AB / BC / CA, ABG / BCG / CAG.

[0103] Scenario 2: Offshore wind power cluster grid connection system Application conditions: Offshore wind farms use a multi-stage power transmission system consisting of submarine cables (20-80km) and onshore transmission lines (50-150km). The capacitive current is large, and single-phase grounding faults and phase-to-phase faults occur frequently.

[0104] System Configuration: Offshore wind farm capacity: 50-300MW (10-20 wind farms); Submarine cable: Cross-linked polyethylene (XLPE) insulation, positive sequence impedance 0.02-0.03+j0.1-0.15Ω / km; Capacitive current: The capacitive current of a single-phase ground fault can reach 50-200A; Voltage levels: 35kV (in-situ power collection), 110-220kV (grid-connected power transmission).

[0105] Expected performance metrics: Submarine cable segment protection accuracy: error <3% (after compensation for submarine cable capacitance effect); Protection accuracy for land-based power lines: error <2%; Suppression of capacitor current effects: Phase angle control can compensate for ±5° phase shift caused by capacitor current; System reliability: Single wind farm protection reliability >95% during communication interruption; Applicable grounding resistance range: 0-50Ω (seawater grounding impedance is usually <5Ω).

[0106] Scenario 3: Wind power grid connection system in areas with weak power grids Application conditions: Areas with weak power grid structure (such as parts of Northwest and North China), short-circuit ratio (SCR) = 1.3-2.5, large voltage fluctuations, and significant errors in traditional distance protection.

[0107] System Configuration: Short-circuit ratio: SCR = 1.3-2.5 (weak grid); Grid impedance: The equivalent impedance is relatively large, with an X / R ratio of 5-15; Voltage drop: During a fault, the voltage may drop to 0.2-0.5 per unit.

[0108] Phase-locked loop configuration: Enhanced phase-locked loop, operating voltage threshold of 0.1 per unit. Expected performance indicators: When SCR=1.3, the error is <3% (compared to >20% for traditional methods, representing an improvement of over 85%). Phase-locked loop stability: Phase error < ±2° when voltage drops to 0.1 pu; Robustness protection: SCR error variation <1% within the range of 1.3-5.0; Voltage recovery support: Reactive current injection meets the requirements of power grid regulations (I q ≥1.5 (0.9-U)); Subsynchronous oscillation suppression: Phase angle control does not introduce negative damping.

[0109] Scenario 4: Wind-Solar-Storage Multi-Energy Complementary System Application conditions: New power systems that include various converter-type power sources such as wind power, photovoltaics, and energy storage, with high complexity of multi-source coordinated control.

[0110] System Configuration: Wind power capacity: 50-200MW; Photovoltaic capacity: 30-150MW; Energy storage capacity: 10-50MW / 20-100MWh; Coordination levels: station-level coordination (10-millisecond cycle) + system-level coordination (100-millisecond cycle).

[0111] Expected performance metrics: Multi-source phase angle consistency: After convergence, the phase angle deviation of each power source is <3°; Energy storage fast response: Energy storage response time is 5-10 milliseconds, assisting in phase adjustment of wind and solar power; Coordination and optimization effect: The overall apparent impedance error of the system is <1.5% (2-3% for single power supply optimization); Communication fault tolerance: System error <2.5% when communication is interrupted in one of the three power supplies; Adaptability to daytime fluctuations: Photovoltaic output changes from 0-100%, with stable protection accuracy.

[0112] Scenario 5: Power Grid Upgrade and Transformation Application conditions: The upgrade is implemented through software upgrades based on existing relay protection equipment, without the need for hardware replacement, and is suitable for the retrofitting of existing wind farms.

[0113] System Configuration: Protection devices: Retain existing circular impedance characteristics (Mho type) or polygonal distance relays; Fan controller: Upgrade the fan control software and add a phase angle control module; Communication network: Utilize existing SCADA systems or IEC61850 networks; Upgrade Costs: Software upgrade cost per wind turbine < 20% of hardware replacement cost. Expected Performance Indicators: Protection accuracy after modification: error reduced from 10-20% before modification to <2%; Implementation period: <2 weeks for a single wind farm (software upgrade + on-site commissioning); Compatibility: Compatible with mainstream wind turbine brands (Vestas, Siemens Gamesa, Goldwind, Envision, etc.); Return on investment: Reduces losses from false triggering / failure to trigger protection; payback period <1 year. Scalability: Supports the addition of wind farms in the future, with adaptive adjustment of the coordination algorithm.

[0114] This invention also includes a strategy for smoothly switching back to normal operation mode from fault-crossing mode after fault clearance, specifically including: (1) Fault clearing detection: When the negative sequence voltage amplitude drops to less than 10% of the positive sequence voltage and the voltage recovers to more than 0.9 per unit, the fault is determined to be cleared.

[0115] (2) Smooth phase angle transition: An exponential decay strategy is adopted to reduce the current phase angle from the fault crossing target value θ. LVRT Transition to normal operating target value θ normal θ(t)=θ normal +(θ LVRT -θ normal )·e -t / τ .

[0116] The time constant τ = 50ms ensures a transition time of approximately 200ms, thus preventing overcurrent protection from malfunctioning due to sudden current changes.

[0117] (3) Active power recovery: In accordance with the requirements of the power grid regulations, the active power shall be restored to the pre-fault level at a rate not exceeding 10% / s, and the d-axis current reference value shall increase linearly.

[0118] in t is the reference value of the d-axis current before the fault, and t is the time (in seconds) after the fault is cleared.

[0119] (4) Distributed coordinated exit: In the scenario of multiple wind farms, after each wind farm detects that the fault has been cleared, it broadcasts an exit signal and switches to normal operation mode in parallel, and the coordination algorithm is suspended.

[0120] This invention provides a distance protection method for wind power grid-connected systems based on multi-source coordinated current phase regulation. By establishing a unified phase angle relationship between the positive-sequence current of the wind farm and the negative-sequence current at the far end, it achieves effective protection against single-phase grounding faults, phase-to-phase faults, and two-phase grounding faults. Compared with traditional methods, this invention has advantages such as high protection accuracy, strong robustness, good scalability, and good real-time performance. It maintains good protection performance under various operating conditions, including weak grid conditions, different power factors, and multiple wind farms connected to the grid. This invention complies with current power grid regulations and can be implemented based on existing relay protection equipment, providing a reliable and efficient distance protection solution for wind power grid-connected transmission systems.

[0121] The core technical principle of this invention is: by precisely adjusting the phase angle of the output current of the wind farm converter, the imaginary part of the additional impedance in the apparent impedance measured by the relay during asymmetrical faults approaches zero, thereby ensuring that the measured reactance accurately reflects the actual fault distance and maintaining the reliability of distance protection.

[0122] 1. Root cause analysis of the problem In traditional synchronous generators, the amplitude and phase of the fault current during asymmetrical faults are mainly determined by the grid impedance characteristics, making them predictable. However, wind farms are connected to the grid via converters, and the fault current is affected by the control strategy. Its phase angle may deviate from the phase of the grid current, causing the apparent impedance measured by the relay to include the imaginary part of the additional impedance, thus deviating the measured impedance from the actual fault location.

[0123] The phase angle of the additional impedance is determined by the phase difference between the positive-sequence current of the wind farm and the negative-sequence current at the far end. When the phase angles of the two are matched in a specific relationship, the additional impedance contains only a resistive component, and the imaginary part is zero, thereby eliminating interference with distance protection.

[0124] Figure 4 This diagram illustrates the core technical principle of the invention, clearly depicting the complete logic chain from the mechanism of additional impedance generation to phase angle control to eliminate the imaginary part. From Figure 4 It can be seen that the core of this invention lies in: establishing the positive sequence current phase angle of the wind farm. Phase angle with the far-end negative sequence current The precise mathematical relationship between them allows for the setting of differentiated phase angle control strategies for different fault types (AG faults have equal phase angles, AB faults have a 180-degree phase difference, and ABG faults use 14-degree protection zone rotation compensation), eliminating the imaginary part of the additional impedance, and enabling the reactance component of the relay measured impedance to accurately reflect the actual fault distance, thereby achieving the reliability of distance protection during wind farm fault crossing.

[0125] 2. Unified phase angle control strategy This invention establishes a unified phase angle control framework for three common types of asymmetric faults: (1) Single-phase ground fault (AG, BG, CG): It can be seen from the theoretical derivation that when the phase angle of the positive sequence current of the wind farm is equal to the phase angle of the negative sequence current at the far end, the condition is satisfied. = The phase angle of the additional impedance compensation coefficient measured by the grounding impedance relay is zero. At this time, the additional impedance M ag R g It contains only a resistance component and does not affect the accuracy of reactance measurement.

[0126] (2) Phase-to-phase faults (AB, BC, CA): Phase-to-phase faults do not generate zero-sequence current. By analyzing the measurement characteristics of the phase-to-phase impedance relay, it is deduced that when the phase angle of the positive-sequence current of the non-faulted phase (such as phase C in case of AB fault) differs from the phase angle of the negative-sequence current at the far end by 180 degrees, the zero-sequence current is satisfied. = -180°, the phase angle of the phase impedance compensation coefficient is zero, ensuring that the additional impedance contains only the resistive component.

[0127] (3) Two-phase ground fault (ABG, BCG, CAG): Two-phase ground faults simultaneously contain zero-sequence and negative-sequence currents. Theoretical analysis and simulation verification show that even using the same phase angle relationship as inter-phase faults, the compensation coefficient M of the grounding loop impedance is... ag2 The phase angle is still ∠M ag2 ≈28°, resulting in reactance error X=|M ag2 |R g sin(∠M ag2 ).

[0128] This invention employs a protected area rotation compensation strategy, rotating the protected area of ​​the Mho-type distance relay clockwise by 14 degrees. This angle is selected based on the half-angle compensation principle. Using the half-angle θ of the maximum phase angle deviation rot =∠M ag2 Using / 2=28° / 2=14° as the rotation angle, the angle error is symmetrically distributed, reducing the maximum phase angle error from 28 degrees to 14 degrees, and keeping the measured impedance within the correct protection zone.

[0129] 3. Distributed multi-source coordination mechanism When multiple wind farms operate simultaneously on the grid, the current phase angles of each wind farm need to be coordinated and optimized to minimize the overall apparent impedance error of the system. This invention employs a distributed consensus algorithm: (1) Each wind farm forms a communication network and exchanges phase angle information only with neighboring wind farms; (2) Each wind farm performs two optimization objectives simultaneously: (a) through neighborhood consistency terms (a) Coordinate with neighboring wind farms; (b) Through local gradient terms Optimize local apparent impedance error; (3) The iterative update formula is: θ k [n+1]=θ k [n]+ (Consistency term - α gradient term), where =0.1-0.2 is the consistency step size, and α=0.01-0.1 is the local optimization weight; (4) Influence weight w k The allocation is based on the proportion of fault current amplitude of each wind farm, with priority given to optimizing wind farms that contribute the most current. (5) The algorithm converges to the global optimum within 5-10 iterations (50-100ms), and the communication fault tolerance mechanism ensures that it automatically switches to the local control mode when a single point of failure occurs.

[0130] 4. Rapid control implementation This invention employs dq-axis control based on a synchronous rotating coordinate system, and derives the d-axis current reference value from the target phase angle:

[0131] This reverse algorithm directly establishes the mapping relationship between the phase angle and the dq current, avoiding the delay of traditional PI controllers, with a control response time of 20-40ms. When the total current amplitude exceeds the converter capacity limit, an equal-phase proportional normalization strategy is adopted to ensure that the phase angle remains strictly unchanged after limiting, thereby achieving the distance protection accuracy requirements.

[0132] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A wind power grid-connected distance protection method with multi-source coordinated current phase regulation, characterized in that, Includes the following steps: S1: Construct a fault type identification strategy based on sequence voltage phase characteristics. By collecting the three-phase voltage and current of the transmission line, calculate the positive sequence, negative sequence and zero sequence voltage components, and use the phase difference characteristics between the negative sequence voltage and the zero sequence voltage to determine the fault type. The fault types include single-phase grounding fault, phase-to-phase fault and two-phase grounding fault. S2: Construct a remote power grid phase reconstruction method based on inverse inference of negative sequence voltage, utilizing the negative sequence voltage locally measured by the distance protection relay. and line negative sequence impedance Z SL2 The negative sequence current phase angle on the remote grid side is obtained by reverse calculation using impedance voltage drop. ; S3: Construct a unified phase angle optimization framework. Based on the identified fault types and the optimization objective of zero phase angle for the apparent impedance compensation coefficient, establish the positive sequence current phase angle of the wind farm. Phase angle with the far-end negative sequence current The parsing mapping relationship between them: For single-phase ground faults (AG, BG, CG), establish an in-phase control strategy. By configuring the positive-sequence current and the negative-sequence current in phase, the compensation coefficient M of the grounding impedance relay measurement is adjusted. ag The phase angle approaches zero, thus achieving decoupling of the imaginary part from the influence of grounding resistance; For phase-to-phase faults (AB, BC, CA), an anti-phase control strategy is established. By utilizing the inherent phase difference between the positive and negative sequence currents during phase-to-phase faults, the compensation coefficient M measured by the phase-to-phase impedance relay is adjusted. ab The phase angle is zero, eliminating the influence of grounding resistance on the phase-to-phase distance measurement; For two-phase ground faults (ABG, BCG, CAG), a hybrid strategy combining reverse-phase control and rotating compensation of the protected area is established, and settings are configured. In response to the inherent ±14-degree phase deviation introduced by zero-sequence current coupling, a compensation mechanism of rotating the protection zone of the Mho type relay clockwise by 14 degrees is adopted. This rotation angle is determined by statistical analysis of the phase angle of the compensation coefficient within the range of 0-40Ω of grounding resistance, so that the positive and negative deviations are symmetrically distributed, and the maximum error on one side is reduced from 28 degrees to 14 degrees. S4: Construct an analytical generation strategy for current reference values ​​based on phase angle inverse mapping, and generate the target positive-sequence current phase angle. The reference value of reactive current I for low voltage ride-through requirements 1qref The direct-axis current reference value is directly calculated using the inverse analytical algorithm of the synchronous rotating coordinate system dq transformation: in, The positive sequence voltage phase angle detected by the phase-locked loop; S5: Construct an equal-phase proportional normalized current limiting optimization strategy, when the total amplitude of the current reference value is... Exceeding the converter's thermal capacity limit I max When defining the normalization factor The d-axis and q-axis currents are scaled proportionally in sync. and ; S6: Construct a distributed phase angle optimization mechanism for multi-wind farm collaboration. When multiple wind farms are connected to the grid, a neighborhood coordination network is established based on the communication graph topology, and a hybrid iterative strategy combining consensus algorithm and local gradient optimization is adopted. Each wind farm operates according to a preset synchronization period T. coord Phase angle updated every 10ms Driven by both neighborhood information sharing and local cost minimization, the overall apparent impedance measurement error of the system converges rapidly.

2. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to claim 1, characterized in that, The process of constructing the in-phase control strategy for single-phase grounding faults in step S3 includes: Establish an analytical expression for the apparent impedance compensation coefficient of the grounding impedance relay: ， By performing complex field decomposition on the compensation coefficients, their imaginary part is expressed as... ; For a phase A ground fault, the positive sequence current phase angle of the wind farm is set to satisfy... By utilizing the phase synchronization mechanism of positive and negative sequence currents, the first term of the imaginary part of the compensation coefficient is made zero. Combined with the characteristics of the remote power grid current, the sum of the imaginary parts approaches zero, i.e. Im(Mag)≈0, ensuring that the additional impedance caused by the grounding resistance contains only the resistive component Rg, thereby achieving the decoupling and elimination of reactance measurement deviation. For B-phase grounding and C-phase grounding faults, respectively set and This enables a unified control framework for all faulty phases.

3. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to claim 1 or 2, characterized in that, The process of constructing the anti-phase control strategy for inter-phase faults in step S3 includes: Establish an analytical expression for the apparent impedance compensation coefficient of the phase-to-phase impedance relay: ； Based on the inherent anti-phase characteristics of positive-sequence current and negative-sequence current during phase-to-phase faults, i.e. The optimal phase configuration of the positive sequence current of the non-faulty phase is derived. For an A / B phase-to-A fault, the phase angle of the positive sequence current in the non-faulty C phase is set to satisfy... Phase synchronization is constructed by utilizing the anti-phase characteristics of positive and negative sequence currents, making the imaginary part of the compensation coefficient zero, i.e., Im(M ab =0, eliminating the influence of grounding resistance on phase-to-phase distance protection measurements; For phase-to-phase faults (BC and CA), the positive sequence current phase angles of the non-faulty phases A and B are controlled respectively, and the settings are... and The 180-degree phase difference originates from the opposite energy flow direction of the positive-sequence system and the negative-sequence system during phase-to-phase faults. Here, subscripts 1 and 2 represent the positive-sequence component and the negative-sequence component, respectively, W represents the wind farm side, and S represents the grid side.

4. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to any one of claims 1-3, characterized in that, The process of constructing the rotating compensation mechanism for the protection zone in step S3 for a two-phase ground fault includes: For a two-phase ground fault (ABG), the phase coupling effect introduced by the zero-sequence current in the grounding loop is analyzed. Although a configuration is set... The compensation factor M of the grounding loop impedance can be increased. ag2 The amplitude is minimized, but the nonlinear coupling between the zero-sequence current and the positive and negative-sequence currents causes an inherent deviation in the phase angle of the compensation coefficient; By performing Monte Carlo simulation statistical analysis on the compensation coefficient within the grounding resistance range of 0-40Ω, the probability distribution range of the phase angle deviation was determined to be ∠M. ag2 The deviation peak is approximately 28 degrees, which originates from the impedance angle difference between the zero-sequence network and the positive-sequence network. Construct a protected area rotation compensation strategy for Mho-type distance relays, rotating the protected area characteristic curve clockwise by θ. rot =14°, this rotation angle is half the angle of the maximum phase deviation. Based on the principle of symmetry, the positive and negative deviations are evenly distributed on both sides of the boundary of the protected area after rotation, reducing the maximum error on one side from 28 degrees to 14 degrees. The same 14-degree rotation angle is used for both BCG and CAG two-phase ground faults. This unified compensation angle is determined by Monte Carlo simulation based on the similar coupling characteristics of zero-sequence current in different two-phase ground faults and is applicable to the ground resistance range of 0-40Ω. The rotation of the protected area is achieved by modifying the impedance angle parameter in the characteristic equation of the Mho-type relay, specifically by changing the original measured impedance Z. relay Replace with Z relay ·e j14 Alternatively, the measured impedance can be rotated by -14° in a digital relay before being compared with the protection characteristics.

5. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to any one of claims 1-4, characterized in that, The calculation of the current reference value in the synchronously rotating coordinate system in step S4 includes: Based on the relationship between the phase angle and the dq current, the time-domain expression for the positive-sequence current of phase A is: ； From the target phase angle The formula for calculating the d-axis current reference value is as follows: 。 6. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to claim 5, characterized in that, The specific implementation of the equal phase ratio normalization strategy in step S5 is as follows: When the total amplitude of the current reference value is detected When, define the normalization factor k lim = I max / I total ; Simultaneously, the d-axis and q-axis current reference values ​​are scaled proportionally: ； This proportional scaling strategy ensures that the current phase angle remains strictly unchanged after limiting, that is: ； The converter thermal capacity limitation I max The value range is 1.2-1.5 per unit. The lower limit of this range, 1.2pu, is determined based on the design margin of the rated current of the converter, and the upper limit, 1.5pu, is determined based on the short-time overload capability of the IGBT junction temperature not exceeding 125℃ and the 10-second thermal time constant. Under the limiting conditions, the phase angle error is less than 2.5%.

7. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to any one of claims 1-6, characterized in that, When multiple wind farms are connected to the grid, the iterative update strategy of the distributed consensus algorithm in step S6 is as follows: Define a communication graph G = (V, E), where V represents N wind farm nodes and E represents a communication link. A neighborhood relationship is established when the electrical distance between two wind farms k and j is less than a preset communication distance threshold (j∈N). k ; Each wind farm synchronizes according to the preset synchronization period T coord =10ms iteration update phase angle: in The consistency step size is set between 0.1 and 0.2, and this range is determined based on a trade-off between convergence speed and stability. When the value is less than 0.1, convergence is too slow. Oscillations are possible when the value is greater than 0.2; The weight is set to local optimization and ranges from 0.01 to 0.

1. This range ensures that global consistency dominates while retaining local optimization capabilities. The weights are uniform neighborhood weights; Local cost function Influence weight The allocation is based on the proportion of fault current amplitude, with priority given to optimizing wind farms that contribute the most current. When the phase angle changes in adjacent iterations |θ k [n+1]-θ k When [n]|<0.5°, it is considered converged. The convergence time is 50-100ms. This time range is determined based on the synchronization period of 10ms and the number of iterations of 5-10.

8. The wind power grid-connected distance protection method with multi-source coordinated current phase regulation according to claim 7, characterized in that, The fault tolerance mechanism of the distributed consensus algorithm includes: Set the communication timeout threshold T timeout =100ms, when wind farm k does not receive a response from neighboring node j∈N within 10 consecutive synchronization cycles. k When the phase angle information is obtained, the communication link (k, j) is determined to be interrupted; When communication is interrupted, wind farm k automatically selects from its neighborhood set N. k Remove node j from the list and recalculate the neighborhood weights. This allows the algorithm to continue converging; When all communication links of wind farm k are interrupted |N k When |=0, it automatically switches to local control mode, based solely on local gradients. Optimize its own phase angle; After communication is restored, wind farm k automatically rejoins the distributed coordination, employing an exponential smoothing strategy. Used to avoid abrupt changes in phase angle.

9. A distance protection system for a wind power grid-connected system with multi-source coordinated current phase regulation, employing the wind power grid-connected distance protection method with multi-source coordinated current phase regulation as described in any one of claims 1-8, characterized in that, include: The fault detection module is configured to monitor the three-phase voltage and current of the transmission line in real time and determine the fault type by the sequence voltage phase relationship; The phase angle calculation module is configured to determine the phase angle relationship between the positive sequence current of the wind farm and the negative sequence current at the far end based on the fault type, and to infer the far end phase using the negative sequence voltage and line sequence impedance measured at the relay terminal. The current reference value generation module is configured to calculate the d-axis and q-axis current reference values ​​based on the synchronous rotating coordinate system back-calculation algorithm, according to the target phase angle and reactive current reference value, and perform equal phase proportional normalization processing when the converter capacity limit is exceeded. The current control module is configured to use a dq axis decoupling control strategy to convert the current reference value into a converter PWM control signal with a response time of 20-40ms. The distributed coordination module is configured to achieve distributed consistency optimization among multiple wind farms through a communication network, with a synchronization period of 10ms, and uses GPS or IEEE1588 precision time protocol to ensure ±1ms synchronization accuracy. The protection zone compensation module is configured to rotate the protection zone of the Mho type distance relay 14 degrees clockwise when a two-phase ground fault is detected, in order to compensate for the inherent phase angle deviation caused by the zero-sequence current.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the distance protection method for wind power grid-connected systems with multi-source coordinated current phase regulation as described in any one of claims 1-8. The storage medium stores: The fault type discrimination data structure includes the positive sequence voltage amplitude threshold, the phase difference range between the negative sequence voltage and the zero sequence voltage, and the corresponding fault type mapping table. The phase angle control parameter data structure includes the phase angle relationship coefficients corresponding to each fault type, the rotation angle of the protection zone, and the calculation parameters of the dq axis current; Distributed coordination configuration data structure, including communication graph topology adjacency matrix and consistency step size. Local optimization weights Synchronization period T coord and communication timeout threshold T timeout .

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