A method and system for grid-connected control of a wind turbine generator system

Abstract

The application relates to a grid-connected control method and system of a wind turbine generator set. The grid-connected control method comprises: acquiring a grid voltage signal, extracting a fundamental component from the grid voltage signal, and estimating a grid fundamental electrical parameter based on the fundamental component; preliminarily matching a voltage parameter output by a regulating unit with the grid fundamental electrical parameter, and judging whether a preliminary grid-connected condition is satisfied based on a result of the preliminary matching; after the preliminary grid-connected condition is satisfied, acquiring a first voltage instantaneous value output by the regulating unit, a second voltage instantaneous value output by the grid, and a connecting loop electrical parameter, and predicting a grid-connected inrush current peak value based on the first voltage instantaneous value, the second voltage instantaneous value, and the connecting loop electrical parameter; comparing the grid-connected inrush current peak value with a preset safety current threshold value; and when the grid-connected inrush current peak value exceeds the preset safety current threshold value, closing a main circuit breaker and switching a working mode of a power converter to a current slope control mode.

Description

Technical Field

[0001] This application relates to the field of energy management, and in particular to a grid-connected control method and system for wind turbine generators. Background Technology

[0002] Grid connection of wind turbine generators is crucial for ensuring the stable operation of the power system. It requires precise matching of the generator's output voltage, frequency, phase, and other electrical parameters with the real-time state of the power grid. This process primarily relies on the phase-locked loop (PLL) phase-tracking technology of the control system to avoid instantaneous surges during grid connection. However, in areas with dense industrial loads, the complex grid environment presents significant challenges to grid connection control, potentially accelerating equipment aging and triggering operational risks.

[0003] Specifically, in such areas, large industrial users periodically switch on and off high-power nonlinear loads, causing the grid voltage waveform to deviate from the ideal sine wave, resulting in continuous harmonic distortion and instantaneous voltage fluctuations. Traditional phase-locked loop (PLL) phase estimation algorithms are mainly optimized for ideal sine wave or low-harmonic environments. In high-interference scenarios where the total harmonic distortion rate of the grid exceeds 5%, they are unable to effectively filter out high-order harmonic interference, resulting in continuous phase tracking errors and frequency jitter, leading to unstable output phase and frequency signals.

[0004] This signal instability directly affects the accuracy of the pre-grid synchronization check: the control system must strictly compare the phase difference, frequency difference, and amplitude difference between the generating unit and the grid, and only allow grid connection if the difference is within the preset threshold. However, in a high harmonic environment, the fluctuation of the phase-locked loop signal can easily cause the system to momentarily exceed the threshold when approaching the synchronization point, resulting in frequent interruptions of grid connection attempts; or although the preset threshold may be barely met, the actual synchronization accuracy is insufficient. Due to the instantaneous voltage difference between the generating unit and the grid, the current rises sharply in a short period of time, generating an inrush current far exceeding the design expectation at the moment of grid connection.

[0005] Frequent grid interruptions and excessive inrush currents can cause significant physical stress on the power electronic equipment inside the generating units. In particular, the IGBT modules in the converter will experience enormous electrical stress due to the inrush current, leading to instantaneous temperature rise of the chips and mechanical stress on the bonding wires. Furthermore, equipment condition monitoring data shows that the health of power devices is deteriorating at a rate far exceeding normal levels. If the current grid connection strategy continues, a large number of generating units will be shut down in the coming months due to the failure of core converter components, resulting not only in substantial power generation losses but also incurring high maintenance costs. Summary of the Invention

[0006] This application provides a grid-connected control method and system for wind turbine generator sets, which at least solves the problems in the prior art where, when wind turbine generator sets are connected to the grid in a complex grid environment, the non-ideal grid voltage waveform and severe harmonic interference lead to phase tracking errors and frequency jitter in the phase-locked loop, resulting in frequent interruptions of grid connection attempts, excessive grid connection inrush current, severe stress on power electronic equipment, accelerated equipment aging, and increased operational risks.

[0007] In a first aspect, this application provides a grid-connected control method for a wind turbine generator set, which is applied to the wind turbine generator set, wherein the wind turbine generator set includes at least a regulating unit, a main circuit breaker, and a power converter, and includes the following steps:

[0008] Acquire the grid voltage signal, extract the fundamental frequency component from the grid voltage signal, and estimate the fundamental frequency electrical parameters of the grid based on the fundamental frequency component;

[0009] The voltage parameters output by the regulating unit are initially matched with the fundamental electrical parameters of the power grid, and based on the results of the initial matching, it is determined whether the initial grid connection conditions are met.

[0010] After the initial grid connection conditions are met, the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit are obtained. Based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit, the peak value of the grid connection inrush current is predicted.

[0011] The peak value of the grid-connected inrush current is compared with the preset safe current threshold. When the peak value of the grid-connected inrush current exceeds the preset safe current threshold, the main circuit breaker is closed, and at the instant the main circuit breaker is closed, the operating mode of the power converter is switched to the current slope control mode.

[0012] In the current slope control mode, the power converter injects current into the power grid at a preset current slope until grid connection is completed.

[0013] Optionally, predicting the peak grid-connected inrush current based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit includes:

[0014] After the initial grid connection conditions are met, before the main circuit breaker is closed, a weak current pulse is injected into the power grid, and the instantaneous response of the first voltage and the instantaneous response of the first current at the grid connection point are measured.

[0015] Based on the weak current pulse, the first voltage instantaneous response, and the first current instantaneous response, the first transient equivalent impedance of the power grid is identified;

[0016] The electrical parameters of the connection circuit are updated based on the first transient equivalent impedance, and the peak value of the grid-connected inrush current is predicted by combining the first instantaneous voltage value and the second instantaneous voltage value.

[0017] Optionally, in the current slope control mode, the power converter injects current into the grid at a preset current slope until grid connection is completed, including:

[0018] In the current slope control mode, the power converter periodically injects weak current disturbances into the grid and measures the second voltage instantaneous response and the second current instantaneous response at the grid connection point.

[0019] Based on the weak current disturbance, the second voltage instantaneous response, and the second current instantaneous response, the second transient equivalent impedance of the power grid and its rate of change are estimated.

[0020] Based on the weak current disturbance, the second transient equivalent impedance and its rate of change, the voltage trend at the grid connection point is predicted.

[0021] When the voltage trend exceeds the preset safe voltage limit, the current injection slope is reduced to the first injection slope.

[0022] The power converter generates a reference current command based on the first injection slope and adjusts the output current to track the reference current command until grid connection is completed.

[0023] Optionally, in the current slope control mode, the power converter periodically injects weak current disturbances into the power grid, including:

[0024] In the current slope control mode, the power converter periodically injects weak current disturbances with preset frequency characteristics into the power grid;

[0025] The grid disturbance voltage signal and grid disturbance current signal at the grid connection point are collected synchronously, and frequency domain analysis is performed on the grid disturbance voltage signal and the grid disturbance current signal.

[0026] Extract the voltage response component and current response component corresponding to the frequency characteristics of the weak current disturbance;

[0027] The second transient equivalent impedance of the power grid is estimated based on the voltage response component and the current response component.

[0028] Optionally, predicting the voltage trend at the grid connection point based on the weak current disturbance, the second transient equivalent impedance, and its rate of change includes:

[0029] The current weak current disturbance is decomposed into multiple frequency components, which include a fundamental component and several harmonic components.

[0030] Obtain the second transient equivalent impedance of the power grid to each frequency component, and calculate the instantaneous voltage contribution of each frequency component to the voltage at the grid connection point.

[0031] The instantaneous voltage contribution of each frequency component is superimposed to obtain the overall instantaneous waveform of the grid connection point voltage;

[0032] Analyze the overall instantaneous waveform and predict the voltage trend at the grid connection point based on the analysis results.

[0033] Optionally, the analysis of the overall instantaneous waveform and the prediction of the grid connection point voltage trend based on the analysis results include:

[0034] Identify all instantaneous voltage peaks in the overall instantaneous waveform and sort all the instantaneous voltage peaks by time;

[0035] For each instantaneous voltage peak after time sorting, the product of its amplitude and duration is calculated to obtain the stress contribution of a single peak.

[0036] By summing up all the stress contributions, the cumulative stress assessment value of the power device for the overall instantaneous waveform is obtained;

[0037] A prediction model is constructed based on the cumulative stress assessment value and the preset cumulative stress threshold, and the voltage trend at the grid connection point is predicted based on the prediction model.

[0038] Optionally, predicting the grid connection point voltage trend based on the accumulated stress assessment value and a preset accumulated stress threshold includes:

[0039] Real-time monitoring of harmonic components of weak injected current disturbances;

[0040] When multiple harmonic components are detected to undergo abrupt changes, the dynamic adjustment of the prediction model parameters is triggered.

[0041] Based on the dynamically adjusted prediction model, combined with the cumulative stress assessment value and the preset cumulative stress threshold, the voltage trend at the grid connection point is predicted.

[0042] Secondly, this application provides a grid-connected control system for a wind turbine generator set, the system comprising:

[0043] The signal acquisition module is used to acquire the grid voltage signal, extract the fundamental component from the grid voltage signal, and estimate the fundamental electrical parameters of the grid based on the fundamental component.

[0044] The matching judgment module is used to perform a preliminary matching between the voltage parameters output by the regulating unit and the fundamental electrical parameters of the power grid, and to determine whether the preliminary grid connection conditions are met based on the results of the preliminary matching.

[0045] The instantaneous value prediction module is used to obtain the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit after the initial grid connection conditions are met, and to predict the peak value of the grid connection inrush current based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit.

[0046] The operating mode switching module is used to compare the peak value of the grid-connected inrush current with a preset safe current threshold; when the peak value of the grid-connected inrush current exceeds the preset safe current threshold, the main circuit breaker is closed, and at the instant the main circuit breaker is closed, the operating mode of the power converter is switched to the current slope control mode.

[0047] A current slope control module is used to inject current into the power grid at a preset current slope in the current slope control mode until grid connection is completed.

[0048] Thirdly, this application provides a computer device including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method described in the first aspect.

[0049] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0050] Compared with related technologies, the grid connection control method and system for wind turbine generators provided in this application have at least the following technical advantages:

[0051] Before grid connection, the system acquires the grid voltage signal and extracts the fundamental component to estimate the grid fundamental electrical parameters. These parameters are then preliminarily matched with the voltage parameters output by the regulating unit to determine the initial grid connection conditions. Once the initial grid connection conditions are met, the system further acquires the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connecting circuit. Based on these parameters, the peak value of the grid connection inrush current is predicted. When the predicted peak value of the grid connection inrush current exceeds a preset safe current threshold, the system switches the power converter's operating mode to current slope control mode at the instant the main circuit breaker is closed. In this mode, current is injected into the grid at a preset current slope until grid connection is complete.

[0052] In summary, this application accurately predicts the peak value of the grid connection inrush current, identifying potential excessive inrush risks in advance. Furthermore, when an excessive inrush current is predicted, it intelligently switches to a current slope control mode, smoothly injecting current into the grid with a controlled current slope. This reduces the electrical stress on the internal power electronic equipment (especially the power devices in the converter) of the wind turbine generator during grid connection. This not only avoids frequent grid connection attempt interruptions, reduces equipment wear, and extends the service life of power devices, but also reduces the risk of downtime due to equipment aging and high maintenance costs, ultimately improving the grid connection reliability, safety, and economy of wind turbine generators in complex grid environments.

[0053] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0054] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0055] Figure 1 This is a flowchart illustrating a grid-connected control method for a wind turbine generator set according to an exemplary embodiment.

[0056] Figure 2 This is a partial flowchart illustrating step S3 according to an exemplary embodiment.

[0057] Figure 3 This is a flowchart illustrating step S5 according to an exemplary embodiment.

[0058] Figure 4 This is a partial flowchart illustrating step S51 according to an exemplary embodiment.

[0059] Figure 5 This is a flowchart illustrating step S52 according to an exemplary embodiment.

[0060] Figure 6 This is a flowchart illustrating step S524 according to an exemplary embodiment.

[0061] Figure 7 This is a block diagram illustrating a grid-connected control system for a wind turbine generator set according to an exemplary embodiment. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0063] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0064] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0065] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application refers to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. The terms "first," "second," and "third" used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0066] In related technologies, frequent grid interruptions and excessive inrush currents can cause significant physical stress to the power electronic equipment inside the generating unit. In particular, the IGBT modules in the converter will experience enormous electrical stress due to the inrush current, leading to instantaneous temperature rise of the chip and mechanical stress on the bonding wires. Furthermore, equipment status monitoring data shows that the health of power devices is deteriorating at a rate far exceeding normal levels. If the current grid connection strategy continues, a large number of generating units will be shut down in the coming months due to the failure of core converter components, resulting not only in large-scale power generation losses but also incurring high maintenance costs.

[0067] Based on the above, embodiments of the present invention provide a grid-connected control method and system for wind turbine generator sets, which will be described in detail below with reference to specific embodiments and accompanying drawings.

[0068] Example 1

[0069] This invention provides a grid-connected control method for wind turbine generator sets. Figure 1 This is a flowchart illustrating a grid-connected control method for a wind turbine generator set according to an exemplary embodiment. Figure 1As shown, this method is applied to wind turbine generator sets, which typically include a rotor, transmission system, generator, regulating unit, power converter, and control system. The regulating unit is responsible for regulating the voltage and frequency output of the generator to meet grid connection requirements; the main circuit breaker serves as the electrical connection switch between the generator set and the grid, controlling grid connection and disconnection operations; the power converter is the core component for energy conversion and control between the wind turbine generator set and the grid, converting the alternating current output from the generator into alternating current that meets grid requirements and offering multiple operating modes. The method includes the following steps:

[0070] S1. Acquire the grid voltage signal, extract the fundamental component from the grid voltage signal, and estimate the fundamental electrical parameters of the grid based on the fundamental component;

[0071] In this embodiment, the grid voltage signal refers to the voltage waveform data collected from the grid side, which includes the fundamental component and possible harmonic components. The grid fundamental electrical parameters refer to parameters such as the amplitude, frequency, and phase of the grid fundamental voltage. The connection circuit electrical parameters refer to parameters such as the impedance and reactance of the connection lines between the wind turbine generator and the grid. In practical applications, the grid voltage signal is collected in real time by voltage sensors installed at the grid connection point. To extract the fundamental component from the collected grid voltage signal, various signal processing techniques can be employed. For example, digital filters, such as low-pass or band-pass filters, can be used to filter out higher harmonics and noise, thereby obtaining a relatively pure fundamental voltage signal. Furthermore, phase-locked loop (PLL) technology can be used to accurately extract the fundamental component by tracking the fundamental frequency and phase of the grid voltage. Based on the extracted fundamental component, the grid's fundamental electrical parameters, such as the effective value, frequency, and phase angle of the fundamental voltage, can be estimated.

[0072] S2. Perform a preliminary matching between the voltage parameters output by the regulating unit and the fundamental electrical parameters of the power grid, and determine whether the preliminary grid connection conditions are met based on the results of the preliminary matching.

[0073] In this embodiment, the voltage parameters output by the regulating unit, including its amplitude, frequency, and phase, are obtained through the unit's internal measurement system. Preliminary matching involves comparing these unit output parameters with previously estimated grid fundamental electrical parameters. For example, the amplitude difference, frequency difference, and phase difference between the unit voltage and the grid voltage can be calculated. Determining preliminary grid connection conditions typically involves setting a series of preset grid connection thresholds. When these differences are all within their respective threshold ranges, the preliminary grid connection conditions are considered met. For example, the amplitude difference may be less than a certain percentage, the frequency difference less than a certain Hertz value, and the phase difference less than a certain angle value. If these conditions are not met, the regulating unit will continue to adjust its output parameters until the preliminary grid connection conditions are met.

[0074] S3. After the initial grid connection conditions are met, obtain the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit. Based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit, predict the peak value of the grid connection inrush current.

[0075] In this embodiment, the first and second instantaneous voltage values ​​are acquired in real time at the grid connection point using a high-precision synchronous sampling device. Electrical parameters of the connection loop, such as the resistance and inductance of the connecting lines, are obtained through pre-measurement or system design parameters. The method for predicting the peak grid-connection inrush current in this application is based on circuit theory. For example, at the moment of grid connection, the main circuit breaker closes, and an instantaneous voltage difference may exist between the generating unit and the grid. This voltage difference will drive current to flow through the connection loop. Using Ohm's law and Kirchhoff's laws, combined with the impedance characteristics of the connection loop, the inrush current that may be generated at the moment of grid connection can be calculated. Specifically, an equivalent circuit model can be established, treating the generating unit and the grid as two voltage sources, and the connection loop as an impedance. Then, the instantaneous rate of change of current due to the voltage difference at the moment of grid connection is calculated, thereby predicting the peak value of the inrush current.

[0076] S4. Compare the peak value of the grid-connected inrush current with the preset safe current threshold; when the peak value of the grid-connected inrush current exceeds the preset safe current threshold, close the main circuit breaker, and at the instant the main circuit breaker closes, switch the operating mode of the power converter to the current slope control mode.

[0077] In this embodiment, the current slope control mode is a special operating mode of the power converter. In this mode, the rate of change of the converter's output current is strictly controlled to avoid sudden current changes. The safe current threshold is set comprehensively based on the withstand capability of the power devices in the wind turbine generator power converter and the grid's requirements for inrush current. It is the maximum allowable inrush current value preset by the withstand capabilities of both the power converter and the grid. If the predicted peak inrush current is lower than the safe current threshold, the main circuit breaker is directly closed to complete grid connection in the traditional manner. If the predicted peak inrush current exceeds the safe current threshold, it indicates that direct grid connection may damage the equipment or cause disturbance to the grid. In this case, the system adopts a more cautious strategy: at the instant the main circuit breaker closes, the power converter's operating mode immediately switches from voltage control mode or other pre-synchronization modes to current slope control mode. It is important to note that this switch is instantaneous, effectively controlling the current from the initial stage of its rise.

[0078] S5. In the current slope control mode, the power converter injects current into the power grid at a preset current slope until grid connection is completed.

[0079] In this embodiment, under the current slope control mode, the power converter no longer attempts to maintain a fixed output voltage, but instead strictly controls the rate of change of its output current. The preset current slope is a calculated and optimized value that ensures a smooth current rise, thus avoiding large surges. The power converter gradually increases the current injected into the grid according to the preset current slope until it reaches the unit's rated output current or the stable current level required for grid connection. During this process, the control system continuously monitors the voltage and current at the grid connection point to ensure the smoothness of the grid connection process. Grid connection is considered complete when the current injection reaches a stable state and all grid connection conditions are met.

[0080] The technical solution described in the above embodiments, through the synergistic effect of the aforementioned steps, effectively addresses the problem of large grid connection impacts for wind turbine generators in complex grid environments. First, by acquiring the grid voltage signal and extracting the fundamental component, the fundamental electrical parameters of the grid are estimated. This step ensures accurate perception of the grid status and avoids phase tracking errors and frequency jitter that may occur with traditional phase-locked loops in harmonic environments. Second, the voltage parameters output by the regulating unit are initially matched with the fundamental electrical parameters of the grid, and preliminary grid connection conditions are determined. After the preliminary grid connection conditions are met, a prediction mechanism for the peak grid connection inrush current is introduced. By acquiring the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connecting circuit, the peak grid connection inrush current is predicted based on real-time data. Potential impact risks are anticipated before grid connection, allowing for preventative measures. When the predicted peak grid connection inrush current exceeds a preset safe current threshold, the system no longer blindly connects directly to the grid but instead changes its strategy: at the instant the main circuit breaker is closed, the operating mode of the power converter is switched to current slope control mode.

[0081] In current slope control mode, the power converter injects current into the grid at a preset current slope until grid connection is complete. By injecting current gradually, excessive electrical stress on the power electronic equipment (especially power devices) inside the wind turbine generator can be avoided, extending equipment life and reducing the risk of equipment failure and downtime caused by inrush current. Compared to traditional direct grid connection or voltage control modes, current slope control mode can effectively limit the rise rate of grid connection current and reduce the peak value of grid connection inrush current. At the same time, this controlled current injection method also reduces disturbance to the grid, improving the stability and reliability of the grid connection process.

[0082] In summary, the embodiments described above in this application achieve adaptability to complex power grid environments and effective suppression of grid connection impacts. By introducing peak grid connection inrush current prediction, this application enables the system to identify risks in advance. When a high impact risk is predicted, the system intelligently switches to current slope control mode to actively limit the current rise rate, thereby solving the problem of excessive grid connection impacts. This not only improves the success rate of grid connection but also enhances the operational reliability and equipment lifespan of wind turbine generators under complex power grid conditions.

[0083] In one possible design, Figure 2 This is a partial flowchart illustrating step S3 according to an exemplary embodiment. (Refer to the attached diagram.) Figure 2 In step S3, predicting the peak value of the grid-connected inrush current based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit includes:

[0084] S31. After the initial grid connection conditions are met, before the main circuit breaker is closed, a weak current pulse is injected into the power grid, and the instantaneous response of the first voltage and the instantaneous response of the first current at the grid connection point are measured.

[0085] In this embodiment, a weak current pulse refers to a current signal with a small amplitude and short duration, intended to detect the real-time electrical characteristics of the power grid without causing significant disturbance. This weak current pulse can be a square wave, a sine wave, or any other preset waveform, and its amplitude is typically much smaller than the rated output current of the wind turbine generator, for example, it can be set to 0.1% to 0.5% of the rated current. The first voltage instantaneous response and the first current instantaneous response refer to the instantaneous changes in voltage and current generated at the grid connection point after the power grid receives the weak current pulse. These response signals are measured and acquired in real time using high-precision sensors.

[0086] S32. Based on the weak current pulse, the first voltage instantaneous response, and the first current instantaneous response, identify the first transient equivalent impedance of the power grid;

[0087] In this embodiment, the equivalent impedance of the power grid at the grid connection point is calculated using an injected weak current pulse and the measured instantaneous responses of the first voltage and the first instantaneous current, through a specific algorithm (e.g., frequency response analysis based on Fourier transform, system identification algorithm, or least squares method). This first transient equivalent impedance can reflect the dynamic electrical characteristics of the power grid at the moment of grid connection in real time, including its resistance, inductance, and other parameters.

[0088] S33. Update the electrical parameters of the connection circuit based on the first transient equivalent impedance, and predict the peak value of the grid-connected inrush current by combining the first instantaneous voltage value and the second instantaneous voltage value.

[0089] In this embodiment, the identified first transient equivalent impedance is used to correct or replace the original electrical parameters of the connection circuit, so that the model parameters used to predict the peak value of the grid-connected inrush current are closer to the actual operating state of the power grid.

[0090] The technical solution of the above embodiment accurately identifies the real-time first transient equivalent impedance of the power grid by actively injecting a weak current pulse into the power grid before the main circuit breaker closes and measuring the instantaneous response of the power grid to the pulse in real time. The first transient equivalent impedance reflects the actual dynamic electrical characteristics of the power grid at the grid connection point. Compared with preset or static connection circuit electrical parameters, it can more realistically characterize the current state of the power grid. Subsequently, the identified first transient equivalent impedance is used to update the connection circuit electrical parameters, so that the subsequent prediction of the peak grid-connected inrush current can be based on a more accurate power grid model. This solves the problem of prediction deviation caused by relying solely on static parameters, improves the prediction accuracy of the peak grid-connected inrush current, and avoids prediction errors caused by inaccurate parameters.

[0091] In one example, when a wind turbine is preparing to connect to the grid, before the initial grid connection conditions are met and the main circuit breaker is closed, the control system injects a very small, short-duration current pulse into the grid. For example, this pulse could be a square or sine wave with an amplitude of only 0.1% to 0.5% of the rated current and a duration of several milliseconds. Simultaneously, voltage and current sensors at the grid connection point synchronously acquire the grid's first instantaneous voltage and current responses to this weak current pulse. Subsequently, a digital signal processor processes the acquired response signals using Fourier transform or a system identification algorithm to accurately calculate the grid's first transient equivalent impedance at the current moment. For example, algorithms such as least squares or Kalman filtering can be used, combined with the injected current pulse and the measured voltage and current responses, to identify the grid's equivalent impedance model. Once the first transient equivalent impedance is obtained, this impedance value is used to update the electrical parameters of the connected circuits in real time, such as updating the equivalent values ​​of line impedance or transformer impedance. Finally, by combining the updated electrical parameters of the connection circuit with the instantaneous values ​​of the first voltage output from the regulating unit and the second voltage output from the grid, a more accurate prediction of the grid-connected inrush current peak can be made. If the predicted peak value is within the safety threshold, the main circuit breaker is allowed to close, and the grid connection process continues.

[0092] In one possible design, Figure 3 This is a flowchart illustrating step S5 according to an exemplary embodiment. (Refer to the attached document.) Figure 3 Step S5 includes:

[0093] S51. In the current slope control mode, the power converter periodically injects weak current disturbances into the grid and measures the second voltage instantaneous response and the second current instantaneous response at the grid connection point.

[0094] In this embodiment, the weak current disturbance is a small-amplitude current signal superimposed on the main injected current, with an amplitude much smaller than the main injected current, to avoid significantly affecting the normal operation of the power grid. The instantaneous electrical behavior of the power grid under this disturbance is obtained by measuring the instantaneous response of the second voltage and the second instantaneous response of the second current at the grid connection point.

[0095] S52. Based on the weak current disturbance, the second voltage instantaneous response, and the second current instantaneous response, estimate the second transient equivalent impedance of the power grid and its rate of change;

[0096] In this embodiment, estimating the second transient equivalent impedance of the power grid and its rate of change allows for real-time monitoring of the grid's dynamic impedance characteristics. The second transient equivalent impedance reflects the equivalent impedance of the power grid at a specific frequency or time scale, while its rate of change indicates the speed and trend of impedance changes.

[0097] S53. Based on the weak current disturbance, the second transient equivalent impedance and its rate of change, predict the voltage trend at the grid connection point;

[0098] In this embodiment, the voltage trend at the grid connection point is predicted to anticipate whether the voltage at the grid connection point will exceed the safe range. By combining the currently injected weak current disturbance, the real-time impedance of the power grid and its changing trend, a predictive model for the grid connection point voltage is constructed to simulate the possible trajectory of the grid connection point voltage over a future period.

[0099] S54. When the voltage trend exceeds the preset safe voltage limit, reduce the current injection slope to the first injection slope.

[0100] In this embodiment, when the voltage trend exceeds the preset safe voltage upper limit, the injection current rate is actively adjusted to suppress further voltage increases, thereby avoiding overvoltage at the grid connection point. The preset safe voltage upper limit is a threshold set according to grid operation specifications and equipment tolerance; the first injection slope is a smaller slope than the current injection slope, used to slow down the current injection rate.

[0101] S55. The power converter generates a reference current command based on the first injection slope and adjusts the output current to track the reference current command until grid connection is completed.

[0102] In this embodiment, this step ensures that the power converter can accurately inject current into the grid according to the adjusted slope, thereby achieving effective control of the grid connection point voltage.

[0103] The technical solution of the above embodiment achieves real-time perception of the dynamic characteristics of the power grid by introducing periodic weak current disturbances in the current slope control mode. Specifically, firstly, by injecting weak current disturbances and measuring the corresponding instantaneous voltage and current responses, the second transient equivalent impedance of the power grid and its rate of change are dynamically estimated, enabling the system to accurately predict the voltage trend at the grid connection point based on this information and the current weak current disturbances. Secondly, when it is predicted that the voltage trend at the grid connection point may exceed the preset safe voltage limit, the system can respond promptly by reducing the current injection slope to the first injection slope, actively slowing down the current injection rate, thereby effectively suppressing further increases in the grid connection point voltage. This dynamic adjustment mechanism allows the power converter to flexibly adjust the grid connection strategy according to the real-time conditions of the power grid, avoiding voltage overshoot or overvoltage problems that may occur due to fixed-slope injection current, thus solving the voltage fluctuation risk that may occur when the power grid dynamically changes in the basic scheme.

[0104] In one possible design, Figure 4 This is a partial flowchart illustrating step S51 according to an exemplary embodiment. (Refer to the attached diagram.) Figure 4 In step S51, the step of periodically injecting a weak current disturbance into the power grid in the current slope control mode includes:

[0105] S511. In the current slope control mode, the power converter periodically injects weak current disturbances with preset frequency characteristics into the power grid.

[0106] In this embodiment, the weak current disturbance with preset frequency characteristics refers to the superposition of one or more small current signals of specific frequencies when the power converter injects current into the power grid. These preset frequency characteristics are selected based on the characteristics of the power grid, noise distribution, or specific harmonic frequencies that need to be focused on. The purpose is to improve the recognition of the power grid response signal in a complex power grid environment by injecting signals of known frequencies, thereby obtaining the dynamic characteristics of the power grid more accurately.

[0107] S512. Synchronously acquire grid disturbance voltage signals and grid disturbance current signals at the grid connection point, and perform frequency domain analysis on the grid disturbance voltage signals and the grid disturbance current signals;

[0108] In this embodiment, frequency domain analysis involves processing the acquired grid disturbance voltage and current signals. Processing methods include Fourier transform (e.g., Fast Fourier Transform, FFT) or other spectral analysis methods to convert the time-domain signals into frequency-domain signals. This separates the voltage and current components corresponding to the frequency characteristics of the injected weak current disturbance, eliminating the influence of other frequency noise and interference.

[0109] S513. Extract the voltage response component and current response component corresponding to the frequency characteristics of the weak current disturbance.

[0110] In this embodiment, voltage and current components that precisely match the preset frequency characteristics are identified and extracted from the frequency domain analysis results. The voltage and current response components represent the actual response of the power grid to disturbances at a specific frequency.

[0111] S514. Based on the voltage response component and the current response component, estimate the second transient equivalent impedance of the power grid;

[0112] In this embodiment, the ratio of the voltage response component to the current response component at a specific frequency is calculated. For example, for each preset frequency, the extracted voltage response component is divided by the corresponding current response component to obtain the transient equivalent impedance value of the power grid at that frequency. Through the above steps, the impedance characteristics of the power grid at different frequencies can be obtained.

[0113] The technical solution described above overcomes the limitations of traditional instantaneous response measurements, which are susceptible to noise interference and lack accuracy in complex power grid environments. By introducing a weak current disturbance with preset frequency characteristics and combining it with frequency domain analysis, the accuracy and robustness of the second transient equivalent impedance estimation of the power grid are improved. Accurate impedance estimation makes the prediction of voltage trends at the grid connection point more reliable, thereby enabling more timely and accurate adjustment of the current injection slope and effectively avoiding overvoltage or overcurrent risks during grid connection.

[0114] In one example, under current slope control mode, the power converter can superimpose one or more weak sinusoidal current disturbances of a specific frequency (e.g., integer or non-integer multiples of the 50Hz fundamental frequency) onto its output current. For instance, a weak sinusoidal current with an amplitude much smaller than the main current and a frequency of 100Hz can be superimposed. Simultaneously, the voltage and current signals at the grid connection point are sampled at high speed and input to a digital signal processor (DSP). The DSP periodically performs a Fast Fourier Transform (FFT) on the acquired voltage and current signals to obtain their spectral information. From the spectral analysis results, the DSP identifies and extracts the voltage amplitude and phase corresponding to the 100Hz frequency component, as well as the current amplitude and phase. Subsequently, by calculating the ratio of the voltage component to the current component at that frequency (considering amplitude and phase), the second transient equivalent impedance of the grid at that 100Hz frequency can be accurately estimated.

[0115] Understandably, this process can be repeated periodically to track changes in grid impedance in real time, thereby providing dynamically updated impedance information for grid-connected control.

[0116] In one possible design, Figure 5This is a flowchart illustrating step S52 according to an exemplary embodiment. (Refer to the attached document.) Figure 5 Step S52 includes:

[0117] S521. Decompose the currently injected weak current disturbance into multiple frequency components, wherein the frequency components include a fundamental component and several harmonic components.

[0118] In this embodiment, a spectral analysis is performed on the weak current disturbance injected into the power grid by the power converter to identify its fundamental component and various harmonic components. In this application, the decomposition process is implemented through Fast Fourier Transform (FFT) or other signal processing techniques to obtain the energy distribution of the current disturbance at different frequencies.

[0119] S522. Obtain the second transient equivalent impedance of the power grid to each frequency component, and calculate the instantaneous voltage contribution of each frequency component to the voltage at the grid connection point.

[0120] In this embodiment, for each frequency component obtained from the above decomposition, the transient equivalent impedance of the power grid at that frequency is determined. The impedance characteristics of the power grid are usually frequency-dependent; therefore, the power grid will exhibit different impedance values ​​for different fundamental and harmonic frequencies. These impedance values ​​can be obtained through a pre-established power grid model or through real-time measurement and identification. Subsequently, based on the current amplitude and phase of each frequency component, and the transient equivalent impedance of the power grid at that frequency, the instantaneous voltage response generated by that frequency component at the grid connection point is calculated. This calculation typically follows Ohm's law and considers the phase relationship between voltage and current.

[0121] S523. Superimpose the instantaneous voltage contributions of each frequency component to obtain the overall instantaneous waveform of the grid connection point voltage;

[0122] In this embodiment, the instantaneous voltage contributions generated by all fundamental and harmonic frequency components are linearly superimposed. According to the superposition principle, the superposition result of these components is the actual, complex instantaneous voltage waveform at the grid connection point. The overall instantaneous waveform reflects the transient changes and distortions of the grid voltage.

[0123] S524. Analyze the overall instantaneous waveform and predict the voltage trend at the grid connection point based on the analysis results;

[0124] In this embodiment, the obtained overall instantaneous waveform is analyzed in depth, such as identifying key parameters like voltage peak value, RMS value, and harmonic content. Based on these analysis results, the voltage change trend at the grid connection point over a future period is predicted, thereby assessing the voltage stability and safety during the grid connection process.

[0125] The technical solution of the above embodiments meticulously decomposes the weak current disturbance injected into the power grid into fundamental and multiple harmonic components, and obtains the second transient equivalent impedance of the power grid for each frequency component. This allows for the accurate calculation of the instantaneous contribution of each frequency component to the grid connection point voltage, and enables the high-precision reconstruction of the overall instantaneous waveform of the grid connection point voltage. Consequently, it captures the transient fluctuations and distortions in the power grid voltage caused by harmonics, obtaining more comprehensive and refined voltage waveform information, and achieving more precise and accurate prediction of the grid connection point voltage trend.

[0126] In one possible design, Figure 6 This is a flowchart illustrating step S524 according to an exemplary embodiment. (Refer to the attached diagram.) Figure 6 Step S524 includes:

[0127] S5241. Identify all instantaneous voltage peaks in the overall instantaneous waveform and sort all the instantaneous voltage peaks by time.

[0128] In this embodiment, after obtaining the overall instantaneous waveform of the grid connection point voltage, it is first necessary to identify all instantaneous voltage peaks appearing in the waveform. Instantaneous voltage peaks can be positive or negative, representing the maximum or minimum instantaneous voltage value reached within a short period. After identification, these instantaneous voltage peaks are sorted according to their chronological order of appearance for subsequent time-series analysis.

[0129] S5242. For each instantaneous voltage peak after time sorting, calculate the product of its amplitude and duration to obtain the stress contribution of a single peak.

[0130] In this embodiment, amplitude refers to the absolute size of the peak value relative to a certain reference (e.g., zero point or average value), and duration refers to the length of time the peak value is maintained within a specific amplitude range. Through product calculation, the stress contribution of a single voltage peak value to the power device is quantified. This method of calculating stress contribution provides a more comprehensive reflection of the impact of transient voltage changes on the device, rather than just the instantaneous amplitude.

[0131] S5243. Sum up all the stress contributions to obtain the cumulative stress evaluation value of the power device for the overall instantaneous waveform;

[0132] In this embodiment, the accumulated result is the cumulative stress assessment value of the power device based on the overall instantaneous waveform. The cumulative stress assessment value, as a comprehensive indicator, is used to measure the total stress level caused by grid connection point voltage fluctuations to power devices such as power converters over a period of time.

[0133] S5244. Construct a prediction model based on the accumulated stress assessment value and the preset accumulated stress threshold, and predict the voltage trend at the grid connection point based on the prediction model;

[0134] In this embodiment, the prediction model can be a mathematical model, a machine learning model, or a rule-based model. Its purpose is to predict the future trend of the grid connection point voltage based on the relationship between the current accumulated stress assessment value and a preset safety threshold. The preset accumulated stress threshold is a safety upper limit determined based on factors such as the withstand capability of power devices, system design requirements, and operational experience. Through the aforementioned prediction model, it is possible to more accurately determine whether the grid connection point voltage will exceed the safe range.

[0135] The technical solution described above, by introducing the identification of instantaneous voltage peaks in the overall instantaneous waveform of the grid connection point voltage, the calculation of stress contributions, and the assessment of cumulative stress, enables the system to identify potential voltage anomaly risks earlier and more accurately, thereby adjusting the current injection slope in a timely manner to ensure the smoothness and safety of the grid connection process. Specifically, by identifying and sorting the instantaneous voltage peaks by time, all potential high-stress points in the voltage waveform are captured. Calculating the product of the amplitude and duration of each peak allows for a more precise quantification of the impact of a single transient event on the power device, as device fatigue and aging are closely related not only to the instantaneous voltage amplitude but also to the duration of high voltage. The stress contributions of these individual peaks are accumulated to form a cumulative stress assessment value, enabling the system to comprehensively consider the overall impact of all voltage transient events on the power device over a period of time, thus avoiding the shortcomings of focusing only on instantaneous values ​​and ignoring long-term cumulative effects. Finally, a prediction model is constructed based on this cumulative stress assessment value and a preset safety threshold, allowing the prediction of the grid connection point voltage trend to combine a quantitative assessment of the actual stress borne by the power device, thereby enabling a more accurate and reliable prediction of the voltage trend.

[0136] In one example, suppose that during the grid connection of a wind turbine generator, the power converter is in current slope control mode and periodically injects weak current disturbances into the grid to estimate the grid's second transient equivalent impedance and predict the voltage trend at the grid connection point. At a certain moment, by superimposing the instantaneous voltage contributions of each frequency component, the overall instantaneous waveform of the grid connection point voltage is obtained. This waveform may contain multiple high-frequency oscillations or spikes.

[0137] First, the system identifies all instantaneous voltage peaks in the overall instantaneous waveform. For example, within a 10-millisecond sampling period, it identifies 5 positive voltage peaks and 4 negative voltage peaks and records the times when they occur. Subsequently, these peaks are sorted in chronological order.

[0138] Next, for each sorted instantaneous voltage peak, such as a spike with an amplitude of 1.2 times the rated voltage and a duration of 50 microseconds, the system calculates its stress contribution (e.g., 1.2 * 50 = 60). This process is repeated for all identified peaks, and their respective stress contributions are summed to obtain a cumulative stress assessment value. For example, within the aforementioned 10-millisecond period, the cumulative stress assessment value for all peaks is 500.

[0139] The accumulated stress assessment value is then fed into a pre-trained predictive model. This predictive model, which may be a neural network model built based on historical data and power device aging curves, compares the current accumulated stress assessment value with a preset accumulated stress threshold (e.g., a maximum allowable accumulated stress of 600 per 10-millisecond cycle). If the predictive model determines, based on the current accumulated stress assessment value, that the grid connection voltage trend will cause the accumulated stress to exceed the preset threshold within a future time window, an early warning will be triggered.

[0140] For example, if the prediction model predicts that the cumulative stress assessment value will reach 800 within the next 100 milliseconds, exceeding the safety threshold, the system will immediately issue an instruction to reduce the current injection slope of the power converter to the first injection slope to slow down the voltage rise rate, thereby avoiding excessive cumulative stress on the power devices and ensuring the safety of the grid connection process and the long-term reliability of the equipment.

[0141] In one possible design, step S5244 includes:

[0142] S52441, Real-time monitoring of harmonic components of weak injected current disturbances;

[0143] In this embodiment, during the process of the power converter injecting current into the grid at a preset current slope, the spectrum analysis of the injected weak current disturbance is continuously performed to obtain the amplitude and phase information of each harmonic component contained therein. Among them, the weak current disturbance is a small-amplitude, high-frequency current signal superimposed on the main current in addition to the main current injection, and its purpose is to detect the transient response characteristics of the grid.

[0144] S52442. When multiple harmonic components are detected to undergo abrupt changes, the dynamic adjustment of the prediction model parameters is triggered.

[0145] In this embodiment, a sudden change occurs when the amplitude or phase of a harmonic component changes significantly beyond a preset threshold within a short period of time. This typically indicates a significant change in the grid impedance characteristics or load conditions. For example, by comparing the harmonic component at the current moment with the average value at the previous moment or over a period of time, a sudden change is identified if the difference exceeds a specific percentage or absolute value. Once such a sudden change is detected, the system will automatically trigger the parameter adjustment mechanism of the prediction model. Dynamic adjustment specifically includes recalculating the weight coefficients in the model, updating the state variables within the model, or adjusting the model's learning rate according to a preset adaptive algorithm, so that the model can better adapt to the changing grid environment.

[0146] S52443. Based on the dynamically adjusted prediction model, combined with the cumulative stress assessment value and the preset cumulative stress threshold, predict the voltage trend at the grid connection point.

[0147] In this embodiment, when predicting the voltage trend at the grid connection point, a model that has been corrected and optimized by real-time harmonic component change information is used. The cumulative stress assessment value and the preset cumulative stress threshold are used as inputs or references to the prediction model. Together with the dynamically adjusted model, they work to provide more accurate and reliable voltage trend prediction results.

[0148] The technical solution described above captures subtle changes in the transient characteristics of the power grid by real-time monitoring of harmonic components of injected weak current disturbances. When these harmonic components abruptly change, it indicates that the equivalent impedance or load conditions of the power grid may have changed significantly. If the original prediction model parameters are used in this case, the prediction results may deviate from the actual situation. Subsequently, when multiple harmonic component abrupt changes are detected, dynamic adjustment of the prediction model parameters is triggered, enabling the prediction model to self-correct and optimize according to the latest power grid conditions. This ensures that the prediction model can always adapt to the constantly changing power grid environment, helps to more accurately assess the potential stress on power devices during grid connection, and allows for more timely and reasonable adjustment of the current injection strategy during grid connection, effectively avoiding the risk of overvoltage or overcurrent due to inaccurate predictions.

[0149] In summary, the grid-connected control method for wind turbine generators provided in this invention obtains the grid voltage signal and extracts the fundamental component before grid connection, estimates the grid fundamental electrical parameters, and performs preliminary matching with the voltage parameters output by the regulating unit to determine the preliminary grid connection conditions. After the preliminary grid connection conditions are met, the system further obtains the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit, and predicts the peak value of the grid connection inrush current based on these parameters. When the predicted peak value of the grid connection inrush current exceeds a preset safe current threshold, the system switches the operating mode of the power converter to the current slope control mode at the instant the main circuit breaker is closed, and injects current into the grid at a preset current slope in this mode until grid connection is completed.

[0150] Example 2

[0151] Embodiment 2 of the present invention provides a grid-connected control system for a wind turbine generator set. Figure 7 This is a block diagram illustrating a grid-connected control system for a wind turbine generator according to an exemplary embodiment. (Refer to the attached diagram.) Figure 7 The system includes:

[0152] The signal acquisition module 01 is used to acquire the grid voltage signal, extract the fundamental component from the grid voltage signal, and estimate the fundamental electrical parameters of the grid based on the fundamental component.

[0153] The matching judgment module 02 is used to perform a preliminary matching between the voltage parameters output by the regulating unit and the fundamental electrical parameters of the power grid, and to determine whether the preliminary grid connection conditions are met based on the results of the preliminary matching.

[0154] The instantaneous value prediction module 03 is used to obtain the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit after the initial grid connection conditions are met, and to predict the peak value of the grid connection inrush current based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit.

[0155] The working mode switching module 04 is used to compare the peak value of the grid-connected inrush current with the preset safe current threshold; when the peak value of the grid-connected inrush current exceeds the preset safe current threshold, the main circuit breaker is closed, and at the instant the main circuit breaker is closed, the working mode of the power converter is switched to the current slope control mode.

[0156] The current slope control module 05 is used to inject current into the power grid at a preset current slope in the current slope control mode until grid connection is completed.

[0157] In summary, the grid-connected control method and system for wind turbine generators provided in this invention accurately predicts the peak value of the grid-connected inrush current, identifying potential excessive inrush risks in advance. Furthermore, when an excessive inrush current is predicted, it intelligently switches to a current slope control mode, smoothly injecting current into the grid with a controlled current slope. This reduces the electrical stress on the internal power electronic equipment (especially the power devices in the converter) of the wind turbine generator during grid connection. This not only avoids frequent grid connection attempt interruptions, reduces equipment wear, and extends the service life of power devices, but also reduces the risk of downtime and high maintenance costs due to equipment aging. Ultimately, it improves the grid-connected reliability, safety, and economy of wind turbine generators in complex grid environments.

[0158] Example 3

[0159] Embodiment 3 of the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method described in the first aspect.

[0160] Example 4

[0161] Embodiment 4 of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the method described in the first aspect.

[0162] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0163] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A grid-connected control method for a wind turbine generator set, applied to a wind turbine generator set, wherein the wind turbine generator set includes at least a regulating unit, a main circuit breaker, and a power converter, characterized in that, Includes the following steps: Acquire the grid voltage signal, extract the fundamental frequency component from the grid voltage signal, and estimate the fundamental frequency electrical parameters of the grid based on the fundamental frequency component; The voltage parameters output by the regulating unit are initially matched with the fundamental electrical parameters of the power grid, and based on the results of the initial matching, it is determined whether the initial grid connection conditions are met. After the initial grid connection conditions are met, the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit are obtained. Based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit, the peak value of the grid connection inrush current is predicted. The peak value of the grid-connected inrush current is compared with the preset safe current threshold. When the peak value of the grid-connected inrush current exceeds the preset safe current threshold, the main circuit breaker is closed, and at the instant the main circuit breaker is closed, the operating mode of the power converter is switched to the current slope control mode. In the current slope control mode, the power converter injects current into the grid at a preset current slope until grid connection is completed, including: In the current slope control mode, the power converter periodically injects weak current disturbances into the grid and measures the second voltage instantaneous response and the second current instantaneous response at the grid connection point. Based on the weak current disturbance, the second voltage instantaneous response, and the second current instantaneous response, the second transient equivalent impedance of the power grid and its rate of change are estimated. Based on the weak current disturbance, the second transient equivalent impedance and its rate of change, the voltage trend at the grid connection point is predicted. When the voltage trend exceeds the preset safe voltage limit, the current injection slope is reduced to the first injection slope. The power converter generates a reference current command based on the first injection slope and adjusts the output current to track the reference current command until grid connection is completed. Wherein, in the current slope control mode, the power converter periodically injects weak current disturbances into the power grid, including: In the current slope control mode, the power converter periodically injects weak current disturbances with preset frequency characteristics into the power grid; The grid disturbance voltage signal and grid disturbance current signal at the grid connection point are collected synchronously, and frequency domain analysis is performed on the grid disturbance voltage signal and the grid disturbance current signal. Extract the voltage response component and current response component corresponding to the frequency characteristics of the weak current disturbance; The second transient equivalent impedance of the power grid is estimated based on the voltage response component and the current response component.

2. The method according to claim 1, characterized in that, The prediction of the grid-connected inrush current peak value based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit includes: After the initial grid connection conditions are met, before the main circuit breaker is closed, a weak current pulse is injected into the power grid, and the instantaneous response of the first voltage and the instantaneous response of the first current at the grid connection point are measured. Based on the weak current pulse, the first voltage instantaneous response, and the first current instantaneous response, the first transient equivalent impedance of the power grid is identified; The electrical parameters of the connection circuit are updated based on the first transient equivalent impedance, and the peak value of the grid-connected inrush current is predicted by combining the first instantaneous voltage value and the second instantaneous voltage value.

3. The method according to claim 1, characterized in that, The method of predicting the voltage trend at the grid connection point based on the weak current disturbance, the second transient equivalent impedance and its rate of change includes: The current weak current disturbance is decomposed into multiple frequency components, which include a fundamental component and several harmonic components. Obtain the second transient equivalent impedance of the power grid to each frequency component, and calculate the instantaneous voltage contribution of each frequency component to the voltage at the grid connection point. The instantaneous voltage contribution of each frequency component is superimposed to obtain the overall instantaneous waveform of the grid connection point voltage; Analyze the overall instantaneous waveform and predict the voltage trend at the grid connection point based on the analysis results.

4. The method according to claim 3, characterized in that, The analysis of the overall instantaneous waveform, and the prediction of the grid connection point voltage trend based on the analysis results, include: Identify all instantaneous voltage peaks in the overall instantaneous waveform and sort all the instantaneous voltage peaks by time; For each instantaneous voltage peak after time sorting, the product of its amplitude and duration is calculated to obtain the stress contribution of a single peak. By summing up all the stress contributions, the cumulative stress assessment value of the power device for the overall instantaneous waveform is obtained; A prediction model is constructed based on the cumulative stress assessment value and the preset cumulative stress threshold, and the voltage trend at the grid connection point is predicted based on the prediction model.

5. The method according to claim 4, characterized in that, The step of predicting the grid connection point voltage trend based on the accumulated stress assessment value and a preset accumulated stress threshold includes: Real-time monitoring of harmonic components of weak injected current disturbances; When multiple harmonic components are detected to undergo abrupt changes, the dynamic adjustment of the prediction model parameters is triggered. Based on the dynamically adjusted prediction model, combined with the cumulative stress assessment value and the preset cumulative stress threshold, the voltage trend at the grid connection point is predicted.

6. A grid-connected control system for a wind turbine generator set, characterized in that, The system includes: The signal acquisition module is used to acquire the grid voltage signal, extract the fundamental component from the grid voltage signal, and estimate the fundamental electrical parameters of the grid based on the fundamental component. The matching judgment module is used to perform a preliminary matching between the voltage parameters output by the regulating unit and the fundamental electrical parameters of the power grid, and to determine whether the preliminary grid connection conditions are met based on the results of the preliminary matching. The instantaneous value prediction module is used to obtain the first instantaneous voltage value output by the regulating unit, the second instantaneous voltage value output by the grid, and the electrical parameters of the connection circuit after the initial grid connection conditions are met, and to predict the peak value of the grid connection inrush current based on the first instantaneous voltage value, the second instantaneous voltage value, and the electrical parameters of the connection circuit. The operating mode switching module is used to compare the peak value of the grid-connected inrush current with a preset safe current threshold; when the peak value of the grid-connected inrush current exceeds the preset safe current threshold, the main circuit breaker is closed, and at the instant the main circuit breaker is closed, the operating mode of the power converter is switched to the current slope control mode. A current slope control module, configured to, in the current slope control mode, allow the power converter to inject current into the power grid at a preset current slope until grid connection is completed, comprising: In the current slope control mode, the power converter periodically injects weak current disturbances into the grid and measures the second voltage instantaneous response and the second current instantaneous response at the grid connection point. Based on the weak current disturbance, the second voltage instantaneous response, and the second current instantaneous response, the second transient equivalent impedance of the power grid and its rate of change are estimated. Based on the weak current disturbance, the second transient equivalent impedance and its rate of change, the voltage trend at the grid connection point is predicted. When the voltage trend exceeds the preset safe voltage limit, the current injection slope is reduced to the first injection slope. The power converter generates a reference current command based on the first injection slope and adjusts the output current to track the reference current command until grid connection is completed. Wherein, in the current slope control mode, the power converter periodically injects weak current disturbances into the power grid, including: In the current slope control mode, the power converter periodically injects weak current disturbances with preset frequency characteristics into the power grid; The grid disturbance voltage signal and grid disturbance current signal at the grid connection point are collected synchronously, and frequency domain analysis is performed on the grid disturbance voltage signal and the grid disturbance current signal. Extract the voltage response component and current response component corresponding to the frequency characteristics of the weak current disturbance; The second transient equivalent impedance of the power grid is estimated based on the voltage response component and the current response component.

7. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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