Transient overvoltage evaluation method for grid-connected wind power system considering dynamic characteristics of generator unit

Abstract

The application discloses a kind of wind power grid-connected system transient overvoltage evaluation methods considering unit dynamic characteristics, it is related to new energy grid-connected technology field.The method first establishes the wind turbine model considering grid following control and low voltage ride through dynamics, deduces the dynamic constraint condition of reactive current support coefficient;Second, construct the equivalent admittance of unit during fault and embed system original admittance matrix, obtain the modified system impedance matrix;Further based on dynamic constraint condition, the reactive current support coefficient value is revised and impedance matrix is updated, the transient voltage increment caused by unit injection current during fault is calculated;Finally, traverse fault scene output evaluation result.The application realizes decoupling solution with linear network by converting the nonlinear dynamics of unit into equivalent admittance, while significantly improving the calculation efficiency, effectively describes the dynamic mechanism such as direct current bus voltage constraint, and guarantees the accuracy of transient overvoltage evaluation.

Description

Technical Field

[0001] This invention relates to the field of new energy grid-connected power supply or distribution technology, and more specifically, to a transient overvoltage assessment method for wind power grid-connected systems that takes into account the dynamic characteristics of the generating units. Background Technology

[0002] Driven by the global energy transition and the "dual carbon" goal, wind power, as a core component of clean energy, is experiencing a trend of increasing grid-connected capacity. Large-scale wind power clusters have become a typical technological feature of the evolution of new power systems. Unlike traditional synchronous generators that connect directly to the grid via rotating electromagnetic fields, modern wind turbines generally use voltage source converters (VSCs) to interface with the grid. Their dynamic response characteristics are dominated by power electronic control strategies, and their physical mechanisms in scenarios such as fault ride-through and power regulation differ fundamentally from those of traditional units. When a power system encounters an AC-side short-circuit fault, wind turbines need to activate the Low Voltage Ride-Through (LVRT) control strategy to inject reactive power to support the recovery of grid voltage. However, during the recovery phase after the fault is cleared, due to the inherent 20-40 millisecond delay in switching from LVRT control mode to normal operation mode, the turbines will continuously inject excessive reactive power into the grid. This can easily lead to transient overvoltage (TOV) after interacting with inductive components of the system. This phenomenon has become a key technical bottleneck that threatens the insulation safety of equipment and can even cause system voltage collapse.

[0003] Existing transient overvoltage assessment methods can be mainly divided into two categories: one is based on electromagnetic transient simulation, which uses tools such as PSCAD / EMTDC and BPA to perform detailed modeling of the system, achieving high assessment accuracy. However, the computational load is enormous when traversing multiple nodes and multiple fault types, making it difficult to meet the needs of engineering practice for rapid assessment. The other is based on analytical models, which improves computational efficiency through simplification methods such as Thevenin equivalence and impedance matrices. However, most of these methods ignore the dynamic response characteristics of wind turbines, such as DC bus voltage fluctuations, phase-locked loop dynamic characteristics, and LVRT switching delays, leading to significant assessment errors and making them unsuitable for high-proportion wind power grid-connected scenarios. The root cause of these problems is that existing methods cannot effectively characterize the dynamic interaction mechanism of strongly nonlinear coupled equipment within wind farms. Furthermore, when facing the traversal analysis of multi-node fault scenarios in large-scale power systems, conventional exhaustive methods suffer from the curse of computational dimensionality and efficiency bottlenecks, failing to meet the dual demands of real-time performance and accuracy in engineering practice. Therefore, constructing a transient overvoltage assessment method system that fully considers the dynamic characteristics of the unit and has both decoupling analysis capability and computational efficiency is of great theoretical value and practical significance for ensuring the safe grid-connected operation of large wind power clusters. Summary of the Invention

[0004] The present invention provides a transient overvoltage assessment method for wind power grid-connected systems that considers the dynamic characteristics of the unit, so as to balance the accuracy of the assessment model and the efficiency of calculation, and solve the problem of difficult overvoltage risk assessment for large-scale wind power grid-connected systems.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for assessing transient overvoltage in a wind power grid-connected system considering the dynamic characteristics of the generating unit includes the following steps:

[0007] S1. Establish a transient steady-state equivalent model of the wind turbine considering the grid following control strategy and low voltage ride-through dynamics, and derive the dynamic constraint conditions for the reactive current support coefficient k based on the dynamic equation of the DC bus voltage of the unit converter.

[0008] S2. Based on the aforementioned equivalent model of the wind turbine's transient steady state, the equivalent admittance of the wind turbine during the fault period is constructed by decomposing the injected current into a linear component and a constant offset component. ;

[0009] S3. Constructing the original admittance matrix Y of the wind power grid-connected system based on the nodal voltage method. orig and the equivalent admittance By embedding the corresponding wind turbine grid connection node into the original admittance matrix, the admittance matrix is ​​corrected to obtain the corrected admittance matrix. And the corrected admittance matrix Inverse the system impedance matrix Z. mod ;

[0010] S4. Based on the dynamic constraints, dynamically correct the reactive current support coefficient k, and update the equivalent admittance using the corrected reactive current support coefficient. and the system impedance matrix Z mod Complete the system impedance matrix Z mod Dynamic correction;

[0011] S5. Utilizing the dynamically corrected system impedance matrix Z mod Calculate the transient voltage increment ΔU caused by the injected current of the wind turbine during the fault period. TOV ;

[0012] S6. Traverse all preset fault scenarios of all nodes in the wind power grid-connected system, based on the transient voltage increment ΔU TOV The system determines and outputs the maximum transient overvoltage level, corresponding fault location, and risk level, thus completing the transient overvoltage assessment.

[0013] Furthermore, in step S1, the method for establishing the equivalent model of the wind turbine's transient steady state includes:

[0014] Treating the wind turbine as a voltage source converter, the output current of the unit during the transient period is expressed as:

[0015]

[0016] in, This refers to the unit's output current during the transient period. This refers to the rated capacity of the wind turbine generator set; This is the maximum allowable current of the converter; The imaginary unit; Reference command for reactive current components in a synchronous rotating coordinate system;

[0017] The reactive current component reference command The following relationship must be satisfied:

[0018]

[0019] in, This is the voltage at the grid connection point of the wind turbine.

[0020] Furthermore, in step S2, the equivalent admittance of the wind turbine during the fault period... The derivation process is as follows: Based on the current characteristics in low voltage ride-through mode, the unit injection current during the fault period is equivalent to a current source related to the voltage deviation at the grid connection point, and then the equivalent admittance is obtained. ,in This is the equivalent reactance of the unit.

[0021] Furthermore, in step S3, the specific method for correcting the admittance matrix is ​​as follows:

[0022] For each wind turbine grid connection node i, its equivalent admittance is superimposed onto the self-admittance element of the corresponding node in the original admittance matrix, i.e. , where i=1,2,...,h; h is the total number of wind turbine grid connection nodes; For the corrected admittance matrix The element in the i-th row and i-th column; Y is the original admittance matrix orig The element in the i-th row and i-th column; Let be the equivalent admittance of the i-th wind turbine unit;

[0023] Corrected admittance matrix With the system impedance matrix Z mod Satisfying Relationship: .

[0024] Furthermore, in step S1, the method for establishing the dynamic constraint conditions for the reactive current support coefficient k includes:

[0025] The following dynamic equation for the DC bus capacitor voltage is established:

[0026]

[0027] in, This is the DC bus capacitance value; This is the DC bus voltage; This is the derivative of the DC bus voltage with respect to time. This refers to the voltage at the grid connection point. This refers to the active current component; Input mechanical power to the wind turbine;

[0028] Then, the dynamic constraint conditions for the reactive current support coefficient k are established:

[0029]

[0030] Furthermore, in step S4, the specific formula for dynamically correcting the reactive current support coefficient k is as follows:

[0031]

[0032] in, 1.5 represents the corrected reactive current support coefficient for the i-th wind turbine unit; 1.5 and 3 are the lower and upper limits of the reactive current coefficient specified in the standard, respectively. This represents the maximum value of the dynamic component of the DC current. Let be the voltage at the grid connection point of the i-th generating unit.

[0033] Furthermore, in step S5, for any evaluation node i, its transient voltage increment for:

[0034]

[0035] in, The corrected system impedance matrix Z mod The mutual impedance element between node i and fault point f; The change in injected current at fault point f is denoted as .

[0036] Furthermore, the change in injected current at fault point f The calculations take into account the voltage drop at the moment of fault occurrence; and the mechanism of the transient voltage increment includes the control hysteresis effect during the fault recovery phase, which manifests as the injected current into the unit after the fault is cleared. satisfy:

[0037]

[0038] in, This is the time to clear the fault; Delay for switching to low voltage ride-through mode; This refers to the unit's output current during the fault. This refers to the grid connection point current under normal operating conditions.

[0039] Furthermore, the preset fault scenario is a three-phase symmetrical metallic grounding fault, and under this fault scenario, the change in injected current at fault point f is... The calculation formula is:

[0040]

[0041] in, The self-impedance of the fault point f in the original impedance matrix of the system; The mutual impedance between fault point f and node i; Let be the change in current at node i; and n be the total number of nodes in the system.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] (1) This invention achieves linear decoupling of nonlinear dynamic characteristics, balancing accuracy and efficiency. By establishing a unit model that considers grid following control and low-voltage ride-through dynamics, this invention derives the dynamic constraints for the reactive current support coefficient k and transforms the strong nonlinear dynamic characteristics of the wind turbine into an equivalent admittance form embedded in the system's original admittance matrix. This method decouples the unit's dynamic model from the grid's linear network equations, preserving accurate descriptions of key dynamic mechanisms (DC voltage constraints, reactive power priority strategy) and avoiding significant errors in traditional analytical models. Furthermore, it replaces the iterative solution of the time-domain differential equations of the entire system with matrix operations, overcoming the computational efficiency bottleneck faced by traditional electromagnetic transient simulations and making it suitable for rapid evaluation of large-scale systems.

[0044] (2) The introduction of dynamic constraints on the DC bus voltage enhances the model's adaptability to operating conditions. This invention does not use a fixed reactive current coefficient, but rather derives a dynamic correction formula for the reactive current support coefficient k based on the dynamic power balance equation of the DC bus capacitor voltage. This formula comprehensively considers multiple factors such as the converter's maximum allowable current, the rate of change of DC voltage, and mechanical power input, and can adaptively adjust the value of k according to the actual operating conditions during a fault (such as voltage drop depth and energy imbalance degree). This effectively avoids overestimation or underestimation of the reactive current support due to neglecting converter capacity limitations, significantly improving the physical accuracy of the evaluation results.

[0045] (3) When calculating the transient voltage increment, this invention fully considers the inherent delay (usually 20~40ms) in the switching from low voltage ride-through mode to normal operation mode after fault clearance. By quantitatively evaluating the interaction between the high reactive current continuously injected by the unit and the inductive components of the system during this period, this invention can accurately capture the peak value of "temporary overvoltage" that often overlooked by traditional methods and appears at the moment of fault recovery, providing a more reliable theoretical basis for insulation coordination and risk prevention and control of wind power grid-connected systems.

[0046] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, embodiments of the present invention are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1This is a schematic diagram of the transient overvoltage assessment method for wind power grid-connected systems provided in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0050] This invention provides a transient overvoltage assessment method for wind power grid-connected systems that considers the dynamic characteristics of the generator unit. This method constructs a refined equivalent model of the wind turbine generator unit, introduces dynamic constraints on DC bus voltage to correct the reactive current support coefficient, and combines impedance matrix correction technology to achieve rapid solution of multi-node fault scenarios.

[0051] like Figure 1 As shown, the method in this embodiment includes the following steps:

[0052] S1. Establish a transient steady-state equivalent model of the wind turbine considering the grid following control strategy and low voltage ride-through dynamics, and derive the dynamic constraint conditions for the reactive current support coefficient k based on the dynamic equation of the DC bus voltage of the unit converter.

[0053] This invention focuses on wind turbine generators employing a grid-following (GF) control strategy. The core control structure consists of a phase-locked loop (PLL), a power outer loop, and a current inner loop. The PLL synchronizes the generator with the grid by tracking the voltage phase at the grid connection point. The power outer loop uses a constant active power (P) - constant reactive power (Q) control mode, outputting d-axis and q-axis current reference commands to the current inner loop. The current inner loop adjusts the converter valve-side potential through a proportional-integral (PI) regulator, enabling rapid tracking of the output current to the reference commands, ultimately completing the power closed-loop control.

[0054] Under steady-state operation, the unit output current is:

[0055]

[0056] in, For the grid connection point current phasor; This refers to the rated capacity of the wind turbine generator set; and They are respectively Current components along the d-axis (active) and q-axis (reactive) in a synchronous rotating coordinate system; It is the imaginary unit.

[0057] According to GB / T 36995-2018 "Test Procedure for Low Voltage Ride-Through Capability of Wind Turbine Generators", the low voltage ride-through capability of wind turbine generators must meet the following core requirements: when the grid connection point voltage drops to 0.9 pu or above, the generator should maintain normal operation; when the voltage drops to between 0.2 and 0.9 pu, the generator should continue to operate and inject reactive power to support voltage recovery; when the voltage drops below 0.2 pu, the generator should continue to operate for at least 0.15 seconds and inject the maximum possible reactive power. Therefore, when the grid connection point voltage Upcc drops below 0.9 pu, the generator should immediately switch to low voltage ride-through (LVRT) mode, and the control strategy should switch from "constant active power - constant reactive power" mode to "reactive power priority - overcurrent protection" mode, prioritizing reactive power injection to support grid voltage recovery. During a fault, to achieve rapid tracking of the grid voltage phase, the PLL switches to fast tracking mode, increasing the dynamic response speed by increasing the proportional coefficient of the PI regulator. At this time, the response time of the inner current loop is still in the millisecond range, much shorter than the fault duration (typically tens to hundreds of milliseconds). Therefore, the reactive current reference command in LVRT mode... The rules for determining the value are as follows:

[0058]

[0059] Where k is the reactive current support coefficient; The voltage at the grid connection point of the wind turbine; I max 0.9 is the maximum allowable current of the converter (usually taken as 1.1~1.5 pu); 0.9 is the per-unit value of the voltage start-up threshold for low voltage ride-through mode.

[0060] To ensure converter safety, the output current must meet the amplitude constraint, i.e., the active current command. It should meet the following requirements:

[0061]

[0062] Therefore, the current phasor injected by the wind turbine into the grid during the fault (i.e., the output current of the unit during the transient period) It can be represented as:

[0063]

[0064] Furthermore, to derive the dynamic constraints on the k-value, the dynamic mechanism of the DC bus voltage needs to be analyzed. The DC bus capacitor of the wind turbine converter is a key component for maintaining system power balance, and its voltage dynamic characteristics directly affect the unit's operational stability and current output capability. According to the power balance principle, the DC bus capacitor voltage... The dynamic equation is:

[0065]

[0066] in, This is the DC bus capacitance value; i is the derivative of the DC bus voltage with respect to time; dc,in and i dc,out These are the DC bus input and output currents, respectively; P e The output power (P) of the AC side of the converter e =U pcc i d ); To input mechanical power to the wind turbine.

[0067] P e =U pcc i d Substituting into the above equation and rearranging, we get:

[0068]

[0069] During fault ride-through, new energy generating units are required to prioritize reactive current output. However, this control strategy may lead to power imbalance between the grid-side converter and the rotor-side converter. To ensure DC bus voltage stability, it is necessary to limit the reactive current of the grid-side converter. d =i df Substitution The constraints for the reactive current command can be obtained by rearranging the data:

[0070]

[0071] The aforementioned Substituting into the above equation, the dynamic constraint condition for the reactive current support coefficient k is derived as follows:

[0072]

[0073] The above equation shows that the value of k is not only related to the voltage drop depth at the grid connection point, but also subject to the combined constraints of dynamic factors such as the DC bus voltage change rate, mechanical power input, and the maximum allowable current of the converter. When the DC bus voltage change rate increases, the upper limit of k will decrease to avoid converter overcurrent; conversely, when the DC bus voltage is stable, k can take a larger value to enhance the voltage support effect. By introducing this dynamic constraint, this paper can achieve dynamic correction of the value of k, thereby improving the accuracy of the evaluation model.

[0074] S2. Based on the aforementioned equivalent model of the wind turbine's transient steady state, the equivalent admittance of the wind turbine during the fault period is constructed by decomposing the injected current into a linear component and a constant offset component. .

[0075] In an inductively dominated network, voltage amplitude and reactive power are strongly coupled. The more surplus reactive power during fault recovery, the more severe the temporary overvoltage. During steady-state operation of renewable energy units, they must generate a certain amount of reactive power to support the grid connection voltage while simultaneously generating active power. Since this paper primarily focuses on the severity of overvoltage, it can be assumed that the units operate under light load conditions during steady-state operation, and that all renewable energy capacity is used to provide reactive power support during faults. .

[0076] Will Substitution The current injected into the new energy system during the fault period can be obtained as follows:

[0077]

[0078] Combination We can obtain:

[0079]

[0080] Assume the rated voltage of the power grid before the fault is U. grid =1.0pu, define the grid connection point voltage deviation ΔU=U pcc -U grid =U pcc -1, then 0.9-U pcc =-(ΔU+0.1). Substituting into the above equation and simplifying, we get:

[0081]

[0082] The injected current during a fault can be decomposed into a linear component related to the voltage deviation and a constant offset component. Furthermore, the equivalent admittance of the wind turbine during a fault can be obtained:

[0083]

[0084] In the formula: The equivalent reactance of the unit is used to simplify the dynamic characteristics of the wind turbine and correct the system impedance matrix for global analysis.

[0085] S3. Constructing the original admittance matrix Y of the wind power grid-connected system based on the nodal voltage method. orig and the equivalent admittance By embedding the corresponding wind turbine grid connection node into the original admittance matrix, the admittance matrix is ​​corrected to obtain the corrected admittance matrix. And the corrected admittance matrix Inverse the system impedance matrix Z. mod .

[0086] First, construct the original admittance matrix Y of the wind power grid-connected system.orig (The dimension is n×n, where n is the number of nodes).

[0087] The original admittance matrix Y orig This paper only characterizes the electrical characteristics of the inherent components of the power grid and does not consider the dynamic effects of wind turbines. Therefore, the equivalent admittance Y of the wind turbines proposed in this paper needs to be considered. eq,i This is embedded within the system to correct the admittance matrix. The specific correction strategy is as follows: for each wind turbine grid connection node i (i=1,2,...,h; h is the number of wind turbine grid connection nodes), its equivalent admittance Y is... eq,i The self-admittance elements are superimposed onto the corresponding nodes of the original admittance matrix. The self-admittance elements of the corrected admittance matrix satisfy:

[0088]

[0089] in, This refers to the element in the i-th row and i-th column of the corrected admittance matrix; This represents the element in the i-th row and i-th column of the original admittance matrix; Let be the equivalent admittance of the i-th wind turbine.

[0090] Subsequently, the modified admittance matrix is ​​inverted to obtain the system impedance matrix, which includes the dynamic characteristics of the wind turbine: This matrix contains the impact of the dynamic characteristics of the wind turbine on the system impedance.

[0091] S4. Based on the dynamic constraints, dynamically correct the reactive current support coefficient k, and update the equivalent admittance using the corrected reactive current support coefficient. and the system impedance matrix Z mod Complete the system impedance matrix Z mod Dynamic correction.

[0092] To improve evaluation accuracy, the k value needs to be corrected based on standard specifications and dynamic constraints. Define the dynamic components of the DC current. for:

[0093]

[0094] Based on the constraints derived in step S1 and the reactive current coefficient range (1.5~3.0) specified in national standard GB / T 19963.1-2021, the correction formula for the k value is as follows:

[0095]

[0096] in, is the corrected reactive current support coefficient for the i-th wind turbine unit; The maximum value of the dynamic component of the DC current is determined by the wind turbine parameters and operating conditions. Let be the voltage at the grid connection point of the i-th unit; 1.5 and 3 are the lower and upper limits of the reactive current coefficient, respectively.

[0097] Using the calculated renew And recalculate Z mod This completes the dynamic correction of the system impedance matrix.

[0098] S5. Utilizing the dynamically corrected system impedance matrix Z mod Calculate the transient voltage increment ΔU caused by the injected current of the wind turbine during the fault period. TOV .

[0099] Suppose a three-phase symmetrical metallic ground fault occurs at fault node f, and the voltage change at the fault point is: The change in injected current at fault point f The calculation formula is:

[0100]

[0101] in, The self-impedance of the fault point f in the original impedance matrix of the system; The mutual impedance between fault point f and node i; Let be the change in current at node i (for non-faulty new energy nodes). ); n is the total number of system nodes.

[0102] Based on the corrected impedance matrix, the transient voltage increment at node i can be arbitrarily evaluated. The calculation formula is:

[0103]

[0104] in, The corrected system impedance matrix Z mod The mutual impedance element between node i and fault point f.

[0105] When a fault causes a voltage drop at the grid connection point, the renewable energy source will enter low-voltage recovery mode, sending a large amount of reactive power support voltage to the external system via a switching current command. However, due to the influence of voltage detection and judgment processes, there is a delay of approximately 20-40 ms in the reactive power control switching of the renewable energy source. Therefore, immediately after the fault is cleared, the low-voltage recovery current of the renewable energy source cannot be withdrawn in time, and the unit continues to inject reactive current into the system, causing a temporary overvoltage lasting for tens of milliseconds. That is, the mechanism of this transient voltage increment also includes the control hysteresis effect during the fault recovery phase. After the fault is cleared, due to the delay in LVRT mode switching... (Approximately 20~40ms), unit injected current It manifests as:

[0106]

[0107] in, This is the time to clear the fault; This refers to the unit's output current during the fault. This represents the grid connection point current under normal operating conditions. The transient voltage increment ΔU calculated in this step... TOV This reflects the overvoltage risk during this period.

[0108] S6. By traversing the preset fault scenarios of all nodes in the wind power grid-connected system through a computer program, based on the transient voltage increment ΔU TOV The system determines and outputs the maximum transient overvoltage level, the corresponding fault location, and the risk level, ultimately completing the transient overvoltage assessment.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assessing transient overvoltage in a wind power grid-connected system considering the dynamic characteristics of the generating unit, characterized in that, Includes the following steps: S1. Establish a transient steady-state equivalent model of the wind turbine considering the grid-following control strategy and low-voltage ride-through dynamics, and derive the dynamic constraint conditions for the reactive current support coefficient k based on the dynamic equation of the DC bus voltage of the unit converter: The following dynamic equation for the DC bus capacitor voltage is established: in, This is the DC bus capacitance value; This is the DC bus voltage; This is the derivative of the DC bus voltage with respect to time. This refers to the voltage at the grid connection point. This refers to the active current component; Input mechanical power to the wind turbine; Then, the dynamic constraint conditions for the reactive current support coefficient k are established: in, This is the maximum allowable current of the converter; S2. Based on the aforementioned equivalent model of the wind turbine's transient steady state, the equivalent admittance of the wind turbine during the fault period is constructed by decomposing the injected current into a linear component and a constant offset component. ; S3. Constructing the original admittance matrix Y of the wind power grid-connected system based on the nodal voltage method. orig and the equivalent admittance By embedding the corresponding wind turbine grid connection node into the original admittance matrix, the admittance matrix is ​​corrected to obtain the corrected admittance matrix. And the corrected admittance matrix Inverse the system impedance matrix Z. mod ; S4. Based on the dynamic constraints, dynamically correct the reactive current support coefficient k, and update the equivalent admittance using the corrected reactive current support coefficient. and the system impedance matrix Z mod Complete the system impedance matrix Z mod Dynamic correction; S5. Utilizing the dynamically corrected system impedance matrix Z mod Calculate the transient voltage increment ΔU caused by the injected current of the wind turbine during the fault period. TOV ; S6. Traverse all preset fault scenarios of all nodes in the wind power grid-connected system, based on the transient voltage increment ΔU TOV The system determines and outputs the maximum transient overvoltage level, corresponding fault location, and risk level, thus completing the transient overvoltage assessment.

2. The method according to claim 1, characterized in that, In step S1, the method for establishing the equivalent model of the wind turbine's transient steady state includes: Treating the wind turbine as a voltage source converter, the output current of the unit during the transient period is expressed as: in, This refers to the unit's output current during the transient period. This refers to the rated capacity of the wind turbine generator set; The imaginary unit; Reference command for reactive current components in a synchronous rotating coordinate system; The reactive current component reference command The following relationship must be satisfied: in, This is the voltage at the grid connection point of the wind turbine.

3. The method according to claim 2, characterized in that, In step S2, the equivalent admittance of the wind turbine during the fault period The derivation process is as follows: Based on the current characteristics in low voltage ride-through mode, the unit injection current during the fault period is equivalent to a current source related to the voltage deviation at the grid connection point, and then the equivalent admittance is obtained. ,in This is the equivalent reactance of the unit.

4. The method according to claim 3, characterized in that, In step S3, the specific method for correcting the admittance matrix is ​​as follows: For each wind turbine grid connection node i, its equivalent admittance is superimposed onto the self-admittance element of the corresponding node in the original admittance matrix, i.e. , where i=1,2,...,h; h is the total number of wind turbine grid connection nodes; For the corrected admittance matrix The element in the i-th row and i-th column; Y is the original admittance matrix orig The element in the i-th row and i-th column; Let be the equivalent admittance of the i-th wind turbine unit; Corrected admittance matrix With the system impedance matrix Z mod Satisfying Relationship: .

5. The method according to claim 4, characterized in that, In step S4, the specific formula for dynamically correcting the reactive current support coefficient k is as follows: in, 1.5 represents the corrected reactive current support coefficient for the i-th wind turbine unit; 1.5 and 3 are the lower and upper limits of the reactive current coefficient specified in the standard, respectively. This represents the maximum value of the dynamic component of the DC current. Let be the voltage at the grid connection point of the i-th generating unit.

6. The method according to claim 5, characterized in that, In step S5, for any evaluation node i, its transient voltage increment for: in, The corrected system impedance matrix Z mod The mutual impedance element between node i and fault point f; The change in injected current at fault point f is denoted as .

7. The method according to claim 6, characterized in that, Change in injected current at fault point f The calculations take into account the voltage drop at the moment of fault occurrence; and the mechanism of the transient voltage increment includes the control hysteresis effect during the fault recovery phase, which manifests as the injected current into the unit after the fault is cleared. satisfy: in, This is the time to clear the fault; Delay for switching to low voltage ride-through mode; This refers to the unit's output current during the fault. This refers to the grid connection point current under normal operating conditions.

8. The method according to claim 7, characterized in that, The preset fault scenario is a three-phase symmetrical metallic grounding fault. Under the preset fault scenario, the change in injected current at fault point f is... The calculation formula is: in, The self-impedance of the fault point f in the original impedance matrix of the system; The mutual impedance between fault point f and node i; Let be the change in current at node i; and n be the total number of nodes in the system.

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