Phase-locked loop control method and device of grid-connected converter, controller, storage medium and grid-connected converter

Abstract

The invention provides a phase-locked loop control method and device of a grid-connected converter, a controller, a storage medium and the grid-connected converter. The method comprises the steps of decomposing a q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component after a power grid voltage is acquired; filtering the first q-axis voltage component, and adding the second q-axis voltage component and the filtered first q-axis voltage component to obtain a target q-axis voltage component; and performing phase-locked loop control based on the target q-axis voltage component to obtain a phase-locked loop output phase angle. The phase angle output by the method not only can stably track the power grid reference, but also can quickly adapt to voltage jump, ensures that the grid-connected converter can still keep accurate synchronization with the power grid in a weak power grid scene, and avoids power abnormity or off-grid faults caused by phase angle deviation.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a phase-locked loop control method, device, controller, storage medium, and grid-connected converter for a grid-connected converter. Background Technology

[0002] With the large-scale application of new energy power generation technologies such as photovoltaics and wind power, distributed new energy power plants are mostly connected to the distribution network through grid-connected converters, making weak grid access scenarios increasingly common. On the one hand, new energy resources are mostly distributed in remote areas, requiring long-distance transmission lines to connect to the main grid, leading to increased equivalent impedance at the grid connection point and a decreased short-circuit ratio (SCR), forming a typical weak grid environment. On the other hand, the centralized connection of a high proportion of power electronic equipment further weakens the inertia and voltage support capacity of the grid, making the voltage of weak grids susceptible to disturbances such as power fluctuations and load switching, exhibiting characteristics such as large voltage fluctuation amplitude, high harmonic content, and poor stability. As the core equipment connecting new energy to the grid, the control performance of the grid-connected converter directly determines the grid connection stability and power quality of the new energy power generation system. Therefore, control technologies adapted to the complex operating conditions of weak grids have become a key research focus in the industry.

[0003] Existing phase-locked loop (PLL) control schemes for grid-connected converters can achieve stable phase angle tracking in conventional high-voltage power grid scenarios with high short-circuit ratios and low equivalent impedances, relying on the grid's strong anti-disturbance capabilities and meeting basic grid-connected operation requirements. However, when applied to weak-voltage power grid scenarios, existing PLL control schemes struggle to balance the requirements of low-frequency oscillation suppression and voltage surge tracking. They cannot adapt to the operating characteristics of weak-voltage power grids, which are characterized by large voltage fluctuations and susceptibility to oscillation interference, thus limiting the reliable application of grid-connected converters in weak-voltage power grids. Summary of the Invention

[0004] This invention provides a phase-locked loop (PLL) control method, device, controller, storage medium, and grid-connected converter for a grid-connected converter, to solve the problem of poor voltage change tracking capability of the PLL in grid-connected converters under weak power grid conditions in the prior art.

[0005] In a first aspect, embodiments of the present invention provide a phase-locked loop control method for a grid-connected converter, comprising: Obtain the grid voltage at the common coupling point between the power grid and the grid-connected converter; The grid voltage is transformed by dq to obtain the q-axis voltage component; The q-axis voltage component is decomposed into a first q-axis voltage component and a second q-axis voltage component; The first q-axis voltage component is filtered, and the second q-axis voltage component is added to the filtered first q-axis voltage component to obtain the target q-axis voltage component. Phase-locked loop (PLL) control is performed based on the target q-axis voltage component to obtain the PLL output phase angle.

[0006] Secondly, embodiments of the present invention provide a phase-locked loop control device for a grid-connected converter, comprising: The grid voltage acquisition module is used to acquire the grid voltage at the common coupling point between the grid and the grid-connected converter; The q-axis voltage component extraction module is used to perform dq transformation on the grid voltage to obtain the q-axis voltage component. A q-axis voltage decomposition module is used to decompose the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component. The q-axis voltage filtering module is used to filter the first q-axis voltage component and add the second q-axis voltage component to the filtered first q-axis voltage component to obtain the target q-axis voltage component. The phase angle output module is used for phase-locked loop control based on the target q-axis voltage component to obtain the phase angle output by the phase-locked loop.

[0007] Thirdly, embodiments of the present invention provide a controller, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the phase-locked loop control method for a grid-connected converter as described in any possible implementation of the first aspect above.

[0008] Fourthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the phase-locked loop control method for a grid-connected converter as described in any possible implementation of the first aspect above.

[0009] Fifthly, embodiments of the present invention provide a grid-connected converter, including the controller described in the third aspect above.

[0010] This invention provides a phase-locked loop (PLL) control method, device, controller, storage medium, and grid-connected converter for a grid-connected converter. The method uses a filtered first q-axis voltage component to suppress low-frequency oscillations and address stability issues in weak grids. The unfiltered second q-axis voltage component retains the dynamic characteristics of the voltage signal, ensuring rapid response to high-low voltage crossovers. The target q-axis voltage component obtained by superimposing both components eliminates oscillation interference without losing dynamic information. Finally, PLL control is performed based on this target q-axis voltage component. The output phase angle can stably track the grid reference and quickly adapt to voltage fluctuations, ensuring that the grid-connected converter maintains precise synchronization with the grid even in weak grid scenarios. This avoids power anomalies or grid disconnection faults caused by phase angle deviations, significantly improving the reliable grid connection capability of new energy power generation systems in weak grids. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is an application scenario diagram of the phase-locked loop control method for grid-connected converters provided in this embodiment of the invention; Figure 2 This is a flowchart illustrating the implementation of the phase-locked loop control method for a grid-connected converter provided in this embodiment of the invention. Figure 3 This is a schematic diagram of the phase-locked loop of the grid-connected converter provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the phase-locked loop control device for a grid-connected converter provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0013] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0014] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0015] Figure 1 This diagram illustrates an application scenario of the phase-locked loop control method for a grid-connected converter provided in an embodiment of the present invention. For example... Figure 1 As shown, taking a photovoltaic grid-connected system as an example, the photovoltaic device is connected to the power grid through a grid-connected converter. Under normal circumstances, the phase-locked loop control loop of the grid-connected converter includes a phase-locked loop, an outer current loop, and an inner voltage loop. In the phase-locked loop, the grid voltage U... gAfter coordinate transformation, the q-axis voltage component is obtained. Then, the q-axis voltage setpoint is subtracted from the q-axis voltage component to obtain the q-axis voltage difference. This q-axis voltage difference is input to the PI controller to obtain the frequency setpoint. The frequency setpoint is subtracted from the frequency feedback value to obtain the frequency difference. Finally, the frequency difference is integrated to obtain the phase-locked loop (PLL) phase angle. This PLL phase angle provides a phase reference for coordinate transformation in the outer current loop and inner voltage loop. The grid-connected converter can be a grid-connected inverter or an energy storage converter connected to an energy storage system; no restriction is imposed here.

[0016] When existing phase-locked loop (PLL) control schemes for grid-connected converters are applied to weak grid scenarios, two problems arise. First, low-frequency oscillations easily generated in weak grids can be superimposed on the q-axis voltage signal of the PLL. Existing PLLs have insufficient ability to suppress these oscillation components, leading to significant fluctuations in the PLL output phase angle. In severe cases, this can even cause PLL instability, disrupting the synchronization between the grid-connected converter and the grid. Second, under the frequent voltage surges and drops in weak grids, although existing PLLs attempt to quickly respond to voltage changes to adjust the phase angle, they are limited by the inability to effectively eliminate the continuous interference of oscillation components. This results in a significant decrease in phase angle tracking accuracy. Even if the PLL has a certain dynamic response speed, oscillation components can still cause phase angle calculation errors, leading to abnormal output power of the grid-connected converter and grid disconnection.

[0017] To avoid the aforementioned problems, this application provides a phase-locked loop (PLL) control method for a grid-connected converter. The execution entity of this method is the PLL controller of the grid-connected converter. (See [link to relevant documentation]). Figure 2 The flowchart illustrating the implementation of the phase-locked loop control method for a grid-connected converter provided in this embodiment of the invention is described in detail below: S101: Obtain the grid voltage at the common coupling point between the power grid and the grid-connected converter.

[0018] In this embodiment, the grid voltage U at the common coupling point connecting the grid and the grid-connected converter can be obtained using a voltage sensor. g This ensures that the collected signals reflect the true interaction between the power grid and the converter.

[0019] S102: Perform dq transformation on the grid voltage to obtain the q-axis voltage component.

[0020] Specifically, the collected grid voltage U g The voltage components of the q-axis and d-axis are obtained by transforming the three-phase coordinate system abc to the synchronous rotating coordinate system dq.

[0021] In the synchronous rotating coordinate system of the phase-locked loop (PLL), the q-axis voltage component is directly used as the phase error signal. Its value is used to drive the PLL to adjust the output phase until the q-axis voltage component is zero. Filtering the q-axis voltage component can effectively suppress phase and frequency jitter in the PLL output. If the q-axis voltage component contains harmonics or oscillating components, directly feeding it into the PI controller will cause the output phase to oscillate. After filtering the q-axis voltage component, these interferences are attenuated, and the PLL output becomes more stable.

[0022] S103: Decompose the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component.

[0023] S104: Filter the first q-axis voltage component and add the second q-axis voltage component to the filtered first q-axis voltage component to obtain the target q-axis voltage component.

[0024] In this embodiment, the controller divides the q-axis voltage component into two parts, filters only the first q-axis voltage component, and passes the second q-axis voltage component directly. This solves the problem of response delay caused by full-channel filtering in traditional phase-locked loops, or instability caused by no filtering in weak grid scenarios.

[0025] Specifically, in this embodiment, a fixed allocation ratio can be selected to decompose the first q-axis voltage component and the second q-axis voltage component. For example, the q-axis voltage component can be decomposed according to a 6:4 allocation ratio.

[0026] This embodiment can also dynamically adjust the distribution ratio of the first q-axis voltage component and the second q-axis voltage component. For example, the distribution ratio can be adjusted based on the grid voltage fluctuation parameter. The larger the grid voltage fluctuation parameter, the lower the distribution ratio of the first q-axis voltage component. This allows the phase-locked loop (PLL) to quickly follow the grid voltage change during sudden grid voltage fluctuations, preventing PLL control instability. When the grid voltage is relatively stable, the focus is on attenuating high-frequency noise and subsynchronous oscillations in the q-axis voltage signal, further ensuring the control stability of the PLL. The fluctuation parameter can be the average value or standard deviation of the grid voltage fluctuation.

[0027] After allocating the first q-axis voltage component and the second q-axis voltage component, the controller can use the Kalman filter algorithm to filter the first q-axis voltage component.

[0028] In one possible implementation, the above-described filtering process for the q-axis voltage component may further include: The q-axis voltage component is input into a high-pass filter to obtain the first q-axis voltage component, and the q-axis voltage component is input into a low-pass filter to obtain the second q-axis voltage component. The first q-axis voltage component and the second q-axis voltage component are combined to obtain the target q-axis voltage component.

[0029] Specifically, a high-pass filter can filter out low-frequency oscillations in the q-axis voltage component, improving signal stability. When the mains voltage changes abruptly, its high-frequency components will be transmitted to the output terminal with almost no delay through the high-pass filter path, thus ensuring a fast response.

[0030] S105: Perform phase-locked loop control based on the target q-axis voltage component to obtain the phase angle of the phase-locked loop output.

[0031] Specifically, the target q-axis voltage component is input into a phase-locked loop (PLL) with phase feedforward to obtain the PLL output phase angle.

[0032] As can be seen from the above embodiments, this embodiment uses the filtered first q-axis voltage component to suppress low-frequency oscillations and solve the stability problem of weak grids, while the unfiltered second q-axis voltage component retains the dynamic change characteristics of the voltage signal, ensuring a rapid response to high-low crossovers. The target q-axis voltage component obtained by superimposing the two components eliminates oscillation interference without losing dynamic information. Finally, phase-locked loop control is performed based on this target q-axis voltage component. The output phase angle can stably track the grid reference and quickly adapt to voltage surges, ensuring that the grid-connected converter can maintain precise synchronization with the grid in weak grid scenarios. This avoids power anomalies or grid disconnection faults caused by phase angle deviations, significantly improving the reliable grid connection capability of new energy power generation systems in weak grids.

[0033] In one possible implementation, the specific implementation process of S103 includes: S201: Multiply the q-axis voltage component by the first weighting coefficient to obtain the first q-axis voltage component; S202: Subtract the first q-axis voltage component from the q-axis voltage component to obtain the second q-axis voltage component.

[0034] In this embodiment, the first weighting coefficient is a proportional coefficient used to split the q-axis voltage component, determining the proportion of voltage components participating in the filtering. The value range of the first weighting coefficient is... When the power grid is in a normal state, k A value of 1 can be set to filter the entire q-axis voltage component, thereby improving the robustness of system control. When the power grid enters a fault ride-through state, This is to achieve a balance between response speed and control stability.

[0035] As can be seen from the above embodiments, this embodiment introduces an adjustable weighting mechanism, enabling the phase-locked loop (PLL) to dynamically adjust the ratio of filtered to non-filtered components according to actual grid conditions, thereby optimizing control performance. In weak grids, voltage fluctuations vary over time, making it difficult for fixed filtering strategies to cover all operating conditions. Through the first weighting coefficient, the system can flexibly allocate filtering intensity based on grid conditions. This adjustable decomposition method not only enhances the PLL's adaptive capability but also simplifies the control logic.

[0036] In one possible implementation, prior to S201, the method provided in this embodiment further includes: The depth of voltage anomaly is determined based on the difference between the grid voltage and the reference voltage threshold. The first weighting coefficient is determined based on the voltage anomaly depth, and the voltage anomaly depth is negatively correlated with the first weighting coefficient.

[0037] In this embodiment, the abnormal depth of the grid voltage includes the voltage sag depth and the overvoltage depth; the reference voltage threshold includes the upper voltage limit and the lower voltage limit of a preset voltage range. If the grid voltage is less than the lower voltage limit of the preset voltage range, the lower voltage limit is subtracted from the grid voltage to obtain the voltage difference, and then the voltage difference is divided by the grid rated voltage to obtain the voltage sag depth; if the grid voltage is greater than the upper voltage limit of the preset voltage range, the grid voltage is subtracted from the upper voltage limit to obtain the voltage difference, and then the voltage difference is divided by the grid rated voltage to obtain the overvoltage depth.

[0038] The greater the depth of the grid voltage anomaly, the more severe the grid fault, and the more necessary it is for the phase-locked loop (PLL) to respond quickly to maintain stability. Therefore, the first weighting coefficient should be reduced. Conversely, when the grid is normal or only has small disturbances, the stability of the PLL control should be prioritized, and the first q-axis voltage component passing through the filter should be increased.

[0039] Specifically, after calculating the voltage anomaly depth, the anomaly interval in which the voltage anomaly depth lies is determined. The anomaly interval includes multiple intervals from smallest to largest. Then, based on the pre-stored correspondence between anomaly intervals and weighting coefficients, the weighting coefficient corresponding to the anomaly interval in which the current voltage anomaly depth lies is determined. This method can effectively reduce the amount of computation and improve the response speed of the control loop.

[0040] In one possible implementation, the specific implementation process for determining the first weighting coefficient based on the voltage anomaly depth includes: Determine whether the voltage anomaly depth has been within the current anomaly interval for a duration of a first time. If the voltage anomaly depth has been within the current anomaly interval for a duration of a first time, find the weighting coefficient corresponding to the current depth interval and use it as the first weighting coefficient.

[0041] Specifically, grid voltage often experiences small, random fluctuations. In such cases, the first weighting coefficient frequently switches with minute changes in the depth of the voltage anomaly, causing frequent fluctuations in the target q-axis voltage component, which in turn triggers small oscillations in the phase angle of the phase-locked loop output. Furthermore, the controller's computational load increases with the frequent updates of the first weighting coefficient, potentially leading to control logic stagnation. This further results in glitches in the grid-connected current, affecting power quality. This embodiment introduces an anomaly interval, adjusting the first weighting coefficient only when the voltage anomaly depth exceeds the current interval boundary and enters the next anomaly interval, completely avoiding jitter caused by small fluctuations.

[0042] As can be seen from the above embodiments, this embodiment, by setting a negative correlation between the voltage anomaly depth and the first weighting coefficient, can reduce the first weighting coefficient when the voltage anomaly depth is large (i.e., severe grid fault), allowing more q-axis voltage components to directly enter the control loop, reducing filtering delay, and enabling the phase-locked loop to quickly track voltage changes, avoiding grid instability caused by response hysteresis. Conversely, when the voltage anomaly depth is small (e.g., small fluctuations), the first weighting coefficient is increased to enhance filtering and suppress noise and oscillations. This dynamic adjustment mechanism ensures that the phase-locked loop maintains optimal performance under different disturbance intensities, prioritizing speed during severe faults and stability during minor disturbances. Furthermore, this method achieves continuous monitoring of the grid status by calculating the voltage anomaly depth in real time, improving the predictability and robustness of the system.

[0043] In one possible implementation, the specific implementation process of S104 includes: The dynamic filtering coefficients are determined based on the grid short-circuit ratio; the dynamic filtering coefficients are negatively correlated with the grid short-circuit ratio. The first q-axis voltage component is filtered based on the dynamic filtering coefficients.

[0044] Specifically, the short circuit ratio (SCR) represents the ratio of the short circuit capacity at the grid connection point to the rated capacity of the grid-connected converter. It is a core indicator for measuring grid strength. The larger the SCR value, the stronger the grid; the smaller the SCR value, the weaker the grid.

[0045] The dynamic filtering coefficient is a filtering coefficient matched according to the size of the SCR value. It requires a larger filtering coefficient under weak grid conditions to improve the response speed and meet the needs of large voltage fluctuations in weak grids.

[0046] Specifically, to improve computational efficiency, this embodiment classifies the power grid into weak, medium-intensity, and strong grids based on the short-circuit ratio (SCR) value. A weak grid is defined as an SCR value less than a first value; a medium-intensity grid as an SCR value greater than or equal to the first value but less than a second value; and a strong grid as an SCR value greater than or equal to the second value. The first value is less than the second value. For example, the first value can be 2, and the second value can be 3. The controller can determine the current grid type based on its SCR value and then determine the corresponding dynamic filtering coefficient. A larger SCR value corresponds to a smaller dynamic filtering coefficient, ensuring the stability of the phase-locked loop (PLL) output phase angle when grid voltage fluctuations are small; conversely, a smaller SCR value corresponds to a larger dynamic filtering coefficient, improving the PLL control response speed under weak grid conditions.

[0047] In one possible implementation, this embodiment can design an online SCR identifier to estimate the current short-circuit ratio of the power grid in real time. The SCR identifier can calculate the SCR value online based on the response of the grid voltage to small active power disturbances injected by the grid-connected converter. The controller can update the dynamic filter coefficients based on the real-time SCR value, so that the system can automatically adapt to changes in the grid topology.

[0048] In one possible implementation, the specific implementation process for determining the dynamic filter coefficients based on the grid short-circuit ratio includes: The dynamic filtering coefficients are determined based on the grid short-circuit ratio and the anomaly depth of the grid voltage. The abnormal depth of the grid voltage is positively correlated with the dynamic filtering coefficient, and the grid short-circuit ratio is negatively correlated with the dynamic filtering coefficient.

[0049] Specifically, the short-circuit ratio of the power grid can be negatively proportional to the dynamic filtering coefficient.

[0050] After obtaining the anomaly depth of the grid voltage and the grid short-circuit ratio, based on the formula... Determine the first reference value; among which, M Indicates the first reference value. r This represents the second weighting coefficient. Dt Indicates abnormal depth. SCR This represents the short-circuit ratio of the power grid. Among them, .

[0051] Then based on M The magnitude of the value determines the corresponding dynamic filtering coefficient.

[0052] As can be seen from the above embodiments, this embodiment achieves comprehensive perception of power grid conditions and precise matching of coefficients through a dual-parameter collaborative design of voltage anomaly depth and SCR value. Voltage anomaly depth reflects the severity of voltage deviation from the normal range; a greater anomaly depth indicates a more prominent power grid problem, requiring a larger filter coefficient for rapid response; a smaller anomaly depth indicates a minor problem, allowing for a more appropriate reduction in the filter coefficient to suppress noise. The SCR value reflects the power grid strength; weak power grids require a larger filter coefficient, while strong power grids require a smaller one. The combination of these two parameters can cover more complex operating conditions. For example, in the case of a weak power grid with severe voltage anomalies, the dynamic filter coefficient is set to its maximum value to ensure the fastest response of the phase-locked loop output phase angle; in the case of a strong power grid with minor voltage anomalies, the dynamic filter coefficient is set to a smaller value to balance response and stability. This dual-parameter collaborative logic is more comprehensive and precise than single-parameter settings, avoiding the problem of inappropriate filter coefficient selection caused by single parameters, and making the phase-locked loop control more stable under diverse weak power grid conditions.

[0053] In one possible implementation, prior to S103, the method provided in this embodiment further includes: The grid voltage is filtered to obtain a filtered voltage; If the absolute value of the difference between the filtered voltage and the grid voltage is greater than a preset difference threshold, then the step of decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component is executed.

[0054] In this embodiment, the filtered voltage represents the voltage value obtained after preliminary filtering of the original grid voltage. The filter here is typically a simple low-pass filter designed to capture the fundamental waveform of the voltage. The controller calculates the absolute value of the difference between the fundamental RMS value of the original grid voltage and the RMS value of the voltage after stronger filtering. When this absolute value exceeds a preset difference threshold, it is determined that a voltage abrupt change has occurred, thus requiring the activation of a portion of the phase-locked loop's filtering process.

[0055] When the absolute value is less than the preset difference threshold, the grid voltage is determined to be relatively stable. At this time, the q-axis voltage component in the phase-locked loop can be decomposed instead of being decomposed. Instead, all q-axis voltage components are input into the filter and the filtered q-axis voltage components are used for phase-locked loop control.

[0056] In one possible implementation, the triggering conditions for the above-mentioned partial filtering process may further include: The difference between the original acquired grid voltage and the filtered grid voltage is calculated point by point, and then the average absolute error within a window time is calculated. If the average absolute error is greater than a preset difference threshold, the step of decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component is executed.

[0057] In one possible implementation, another triggering condition for the above-described partial filtering process may include: Real-time monitoring of the grid signal at the common coupling point between the power grid and the grid-connected converter; the grid signal includes grid voltage and / or grid frequency; If the power grid signal exceeds the first preset range, it enters the fault ride-through state, and in the fault ride-through state, the step of decomposing the q-axis voltage component into the first q-axis voltage component and the second q-axis voltage component is performed.

[0058] In this embodiment, fault ride-through state refers to the working mode in which the grid-connected converter does not disconnect from the grid and continues to operate stably and support the grid when the grid signal exceeds the normal operating range. Specifically, it can include high voltage ride-through, low voltage ride-through, overvoltage fault, and undervoltage fault.

[0059] Specifically, when the grid signal is the grid voltage, the first preset range may include an upper voltage limit and a lower voltage limit. If the grid voltage is higher than the upper voltage limit, the grid-connected system is determined to enter a high voltage ride-through state. If the grid voltage is lower than the lower voltage limit, the grid-connected system is determined to enter a low voltage ride-through state.

[0060] Optionally, when the grid signal is the grid frequency, the first preset range may include an upper frequency limit and a lower frequency limit. If the grid frequency is higher than the upper frequency limit, the grid-connected system is determined to have entered a high-voltage ride-through state; or, if the grid frequency shows an upward trend and the rate of change of the grid frequency is greater than a preset rate of change threshold, the grid-connected system is determined to have entered a high-voltage ride-through state. If the grid frequency is lower than the lower frequency limit, the grid-connected system is determined to have entered a low-voltage ride-through state; or, if the grid frequency shows a downward trend and the rate of change of the grid frequency is greater than a preset rate of change threshold, the grid-connected system is determined to have entered a low-voltage ride-through state.

[0061] As can be seen from the above embodiments, this embodiment adds a start condition for the partial filtering process of the q-axis voltage component. The decomposition operation is only performed when the absolute value of the difference between the filtered voltage and the original voltage is greater than a preset difference threshold. This method provides a trigger condition for the phase-locked loop (PLL) control strategy, thereby optimizing the use of computing resources while ensuring performance. In weak power grids, voltage fluctuations are not continuous but occur intermittently; if decomposition and partial filtering control are always enabled, it will increase the processing burden and may introduce unnecessary delays during stable periods. By comparing the pre-filter and voltage difference, the controller can intelligently identify whether a significant voltage change has occurred and trigger the decomposition mechanism only when there is a drastic voltage change, quickly adjusting the PLL response. This conditional triggering method not only reduces the average computational load and improves system efficiency but also ensures that the PLL can prioritize dynamic performance during critical periods (such as voltage changes).

[0062] In one possible implementation, refer to Figure 3The specific implementation process of S105 includes: Subtract the q-axis voltage feedback value U from the target q-axis voltage component. fdb The q-axis voltage difference is obtained. The q-axis voltage difference is input into the first PI controller to obtain the frequency reference value; Subtracting the feedback frequency fn from the frequency reference value yields the frequency difference. Integrating this frequency difference gives the output phase angle of the phase-locked loop. .

[0063] Specifically, the q-axis voltage feedback value U fdb Used to generate a deviation by comparing with the target q-axis voltage component. Normally, the q-axis voltage feedback value is always 0.

[0064] The frequency reference value is the target grid frequency that the phase-locked loop (PLL) aims to track, serving as an intermediate variable connecting voltage deviation and phase output. The feedback frequency fn is the actual grid frequency measured by the PLL in real time, used to compare with the frequency reference value, correct the phase output, and avoid phase angle deviation caused by frequency drift.

[0065] In one possible implementation, after obtaining the target q-axis voltage component, this embodiment not only inputs the target q-axis voltage component into the PI controller, but also directly fine-tunes the frequency reference value through a feedforward path. For example, when the rate of change of the q-axis voltage component is detected to be greater than a preset rate of change threshold, an instantaneous frequency compensation signal is applied to the feedforward path and superimposed on the frequency reference value output by the PI controller. The compensated frequency reference value can further improve the tracking speed of the phase-locked loop for phase changes.

[0066] This embodiment further discloses the specific steps of phase-locked loop (PLL) control based on the target q-axis voltage component, constructing a closed-loop control system that achieves accurate and stable phase angle tracking through PI regulation. The target q-axis voltage component, as input, has undergone partial filtering to achieve both smoothness and speed. After comparison with the given q-axis voltage value, an error signal is generated. This signal is processed by the PI controller, and the output frequency reference value is then compared with the feedback frequency to finally obtain the PLL output phase angle. This control loop ensures dynamic compensation of grid frequency changes, improving the accuracy and robustness of phase angle tracking.

[0067] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0068] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0069] Figure 4 A schematic diagram of the phase-locked loop control device for a grid-connected converter provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 4 As shown, the phase-locked loop control device 100 of the grid-connected converter includes: The grid voltage acquisition module 110 is used to acquire the grid voltage at the common coupling point between the grid and the grid-connected converter. The q-axis voltage component extraction module 120 is used to perform dq transformation on the grid voltage to obtain the q-axis voltage component. The q-axis voltage decomposition module 130 is used to decompose the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component. The q-axis voltage filtering module 140 is used to filter the first q-axis voltage component and add the second q-axis voltage component to the filtered first q-axis voltage component to obtain the target q-axis voltage component. The phase angle output module 150 is used for phase-locked loop control based on the target q-axis voltage component to obtain the phase angle output by the phase-locked loop.

[0070] In one possible implementation, the q-axis voltage decomposition module 130 includes: The first q-axis voltage component acquisition unit is used to multiply the q-axis voltage component by a first weighting coefficient to obtain the first q-axis voltage component; The second q-axis voltage component acquisition unit is used to subtract the first q-axis voltage component from the q-axis voltage component to obtain the second q-axis voltage component.

[0071] In one possible implementation, the first q-axis voltage component acquisition unit further includes: The depth of voltage anomaly is determined based on the difference between the grid voltage and the reference voltage threshold. The first weighting coefficient is determined based on the voltage anomaly depth, and the voltage anomaly depth is negatively correlated with the first weighting coefficient.

[0072] In one possible implementation, the q-axis voltage filtering module 140 is specifically used for: The dynamic filtering coefficients are determined based on the grid short-circuit ratio; the dynamic filtering coefficients are negatively correlated with the grid short-circuit ratio. The first q-axis voltage component is filtered based on the dynamic filtering coefficients.

[0073] In one possible implementation, the phase-locked loop control device 100 of the grid-connected converter further includes a filter activation module for: The grid voltage is filtered to obtain a filtered voltage; If the absolute value of the difference between the filtered voltage and the grid voltage is greater than a preset difference threshold, then the step of decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component is executed.

[0074] In one possible implementation, the phase angle output module 150 includes: Subtract the q-axis voltage feedback value from the target q-axis voltage component to obtain the q-axis voltage difference; The q-axis voltage difference is input into the first PI controller to obtain the frequency reference value; The frequency difference is obtained by subtracting the feedback frequency from the frequency reference value, and the output phase angle of the phase-locked loop is obtained by integrating the frequency difference.

[0075] Figure 5 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 5 As shown, the controller 5 in this embodiment includes a processor 50, a memory 51, and a computer program 52 stored in the memory 51 and executable on the processor 50. When the processor 50 executes the computer program 52, it implements the steps in the aforementioned embodiments of the phase-locked loop control methods for various grid-connected converters, for example... Figure 2 Steps S101 to S105 are shown. Alternatively, when the processor 50 executes the computer program 52, it implements the functions of each module / unit in the above-described device embodiments.

[0076] For example, the computer program 52 may be divided into one or more modules / units, which are stored in the memory 51 and executed by the processor 50 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 52 in the controller 5.

[0077] The controller 5 can be a computing device such as a desktop computer, laptop, handheld computer, or cloud server. The controller 5 may include, but is not limited to, a processor 50 and a memory 51. Those skilled in the art will understand that... Figure 5 This is merely an example of controller 5 and does not constitute a limitation on controller 5. It may include more or fewer components than shown, or combine certain components, or different components. For example, the controller may also include input / output devices, network access devices, buses, etc.

[0078] The processor 50 may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0079] The memory 51 can be an internal storage unit of the controller 5, such as a hard disk or memory of the controller 5. The memory 51 can also be an external storage device of the controller 5, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 5. Furthermore, the memory 51 can include both internal storage units and external storage devices of the controller 5. The memory 51 is used to store the computer program and other programs and data required by the controller. The memory 51 can also be used to temporarily store data that has been output or will be output.

[0080] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0081] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0082] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0083] In the embodiments provided by this invention, it should be understood that the disclosed devices / controllers and methods can be implemented in other ways. For example, the device / controller embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0084] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0085] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0086] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the phase-locked loop control method embodiments of the various grid-connected converters described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0087] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A phase-locked loop control method for a grid-connected converter, characterized in that, include: Obtain the grid voltage at the common coupling point between the power grid and the grid-connected converter; The grid voltage is transformed by dq to obtain the q-axis voltage component; The q-axis voltage component is decomposed into a first q-axis voltage component and a second q-axis voltage component; The first q-axis voltage component is filtered, and the second q-axis voltage component is added to the filtered first q-axis voltage component to obtain the target q-axis voltage component. Phase-locked loop (PLL) control is performed based on the target q-axis voltage component to obtain the PLL output phase angle.

2. The phase-locked loop control method for a grid-connected converter according to claim 1, characterized in that, The step of decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component includes: Multiplying the q-axis voltage component by the first weighting coefficient yields the first q-axis voltage component; Subtracting the first q-axis voltage component from the q-axis voltage component yields the second q-axis voltage component.

3. The phase-locked loop control method for a grid-connected converter according to claim 2, characterized in that, Before multiplying the q-axis voltage component by the first weighting coefficient to obtain the first q-axis voltage component, the method further includes: The depth of voltage anomaly is determined based on the difference between the grid voltage and the reference voltage threshold. The first weighting coefficient is determined based on the voltage anomaly depth, and the voltage anomaly depth is negatively correlated with the first weighting coefficient.

4. The phase-locked loop control method for a grid-connected converter according to claim 1, characterized in that, The filtering process for the first q-axis voltage component includes: The dynamic filtering coefficients are determined based on the grid short-circuit ratio; the dynamic filtering coefficients are negatively correlated with the grid short-circuit ratio. The first q-axis voltage component is filtered based on the dynamic filtering coefficients.

5. The phase-locked loop control method for a grid-connected converter according to claim 1, characterized in that, Before decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component, the method further includes: The grid voltage is filtered to obtain a filtered voltage; If the absolute value of the difference between the filtered voltage and the grid voltage is greater than a preset difference threshold, then the step of decomposing the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component is executed.

6. The phase-locked loop control method for a grid-connected converter according to claim 2, characterized in that, The phase-locked loop control based on the target q-axis voltage component, to obtain the phase-locked loop output phase angle, includes: Subtract the q-axis voltage feedback value from the target q-axis voltage component to obtain the q-axis voltage difference; The q-axis voltage difference is input into the first PI controller to obtain the frequency reference value; The frequency difference is obtained by subtracting the feedback frequency from the frequency reference value, and the output phase angle of the phase-locked loop is obtained by integrating the frequency difference.

7. A phase-locked loop control device for a grid-connected converter, characterized in that, include: The grid voltage acquisition module is used to acquire the grid voltage at the common coupling point between the grid and the grid-connected converter; The q-axis voltage component extraction module is used to perform dq transformation on the grid voltage to obtain the q-axis voltage component. A q-axis voltage decomposition module is used to decompose the q-axis voltage component into a first q-axis voltage component and a second q-axis voltage component. The q-axis voltage filtering module is used to filter the first q-axis voltage component and add the second q-axis voltage component to the filtered first q-axis voltage component to obtain the target q-axis voltage component. The phase angle output module is used for phase-locked loop control based on the target q-axis voltage component to obtain the phase angle output by the phase-locked loop.

8. A controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the phase-locked loop control method for the grid-connected converter as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the phase-locked loop control method for the grid-connected converter as described in any one of claims 1 to 6.

10. A grid-connected converter, characterized in that, Includes the controller as described in claim 8.

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