Wind power converter weak grid synchronization method and system based on injection phase-locked loop

Abstract

The application relates to the technical field of intelligent decision-making, and provides a wind power converter weak power grid synchronization method and system based on an injection type phase-locked loop, which actively injects a disturbance signal into a power grid, analyzes voltage and current responses caused by the disturbance signal in real time, accurately quantifies unknown power grid impedance characteristics, accurately evaluates a current stability margin based on the measured data, dynamically decides an optimal injection signal amplitude and frequency, and ensures that the wind power converter can always adaptively maintain the system in an optimal state with sufficient stability margin when facing any unknown and dynamically changing weak power grid environment, so that the risk of synchronization instability oscillation is eliminated, and the robustness and power quality of grid connection are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of intelligent decision-making technology, and in particular to a method and system for synchronizing wind power converters with weak grids based on injection phase-locked loops. Background Technology

[0002] As the global energy structure shifts towards renewable energy, wind power, as a core component, is experiencing rapid development. Wind farms are often built in remote areas far from load centers, resulting in grid connection points that typically exhibit weak grid characteristics with high impedance and low short-circuit capacity. In this complex grid environment, precise and rapid synchronization between wind power converters and the grid is crucial for ensuring stable system operation and power quality; synchronization failure can lead to oscillations or even grid disconnection.

[0003] To address the challenges posed by weak power grids, phase-locked loops (PLLs), as the core technology for converter synchronous control, have evolved into various advanced topologies. Among them, injection-type PLLs have attracted attention due to their ability to adapt to changes in grid impedance to a certain extent. However, existing injection-type PLL technologies generally suffer from a key bottleneck: their implementation largely relies on a set of fixed injection parameters tuned based on offline analysis and hypothetical grid models. This static control method ignores the fact that grid impedance is actually an unknown dynamic quantity that changes in real time with transmission line switching and regional load variations. Therefore, when grid characteristics change unexpectedly, the fixed injection parameters cannot provide adaptive adjustment. If the actual grid is stronger than preset, excessive injection signals will unnecessarily disturb the grid and degrade power quality. Conversely, if the grid is weaker or exhibits different resonance characteristics, the fixed parameters may not provide sufficient stability margin, resulting in slow dynamic response, or even interaction with grid impedance peaks, triggering subsynchronous oscillations and making the control system itself a cause of instability. Summary of the Invention

[0004] This invention provides a method and system for synchronizing wind power converters in weak grid environments based on an injection-type phase-locked loop (PLL). It actively injects a disturbance signal into the grid and analyzes the resulting voltage and current responses in real time, thereby accurately quantifying the currently unknown grid impedance characteristics. Based on this measured data, it can accurately assess the current stability margin and dynamically determine the optimal amplitude and frequency of the injected signal. In this way, it ensures that the wind power converter can adaptively maintain the system in an optimal state with sufficient stability margin when facing any unknown and dynamically changing weak grid environment, thus eliminating the risk of synchronization instability and significantly improving grid robustness and power quality.

[0005] In a first aspect, the present invention provides a method for synchronizing a wind power converter with a weak grid based on an injection phase-locked loop, comprising: The disturbance signal is injected into the d-axis current reference signal and q-axis current reference signal of the wind power converter and data is collected to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter. Frequency domain data transformation and disturbance response extraction are performed on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. The grid impedance matrix spectrum is obtained by calculating the grid impedance matrix spectrum from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. Stability margin assessment and injection parameter decision-making are performed on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency. Adaptive injection phase-locked loop (PLL) is performed based on optimized injection amplitude and optimized injection frequency to obtain the PLL output phase and PLL output frequency.

[0006] Secondly, the present invention provides a wind power converter weak grid synchronization system based on an injection phase-locked loop, comprising: The data acquisition module is used to inject disturbance signals into the d-axis current reference signal and q-axis current reference signal corresponding to the wind power converter and to acquire data to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter. The disturbance response extraction module is used to perform frequency domain data transformation and disturbance response extraction on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. The grid impedance calculation module is used to calculate the grid impedance from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum to obtain the grid impedance matrix spectrum. The injection parameter decision module is used to perform stability margin assessment and injection parameter decision on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency. An adaptive injection phase-locked loop (PLL) module is used to perform adaptive injection phase-locking based on optimized injection amplitude and optimized injection frequency to obtain the PLL output phase and PLL output frequency.

[0007] Compared with existing technologies, this invention provides a wind power converter synchronization method and system for weak grids based on an injection-type phase-locked loop (PLL). It actively injects a disturbance signal into the grid and analyzes the resulting voltage and current responses in real time, thereby accurately quantifying the currently unknown grid impedance characteristics. Based on this measured data, it can accurately assess the current stability margin and dynamically determine the optimal amplitude and frequency of the injected signal. In this way, it ensures that the wind power converter can adaptively maintain the system in an optimal state with sufficient stability margin when facing any unknown and dynamically changing weak grid environment, thus eliminating the risk of synchronization instability and significantly improving grid robustness and power quality. Attached Figure Description

[0008] One or more embodiments are illustrated by way of example with the corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0009] Figure 1 A flowchart of a wind power converter weak grid synchronization method based on an injection phase-locked loop according to an embodiment of the present invention; Figure 2 A schematic diagram of data flow in a wind power converter weak grid synchronization method based on an injection phase-locked loop according to an embodiment of the present invention; Figure 3 This is a block diagram of a wind power converter weak grid synchronization system based on an injection phase-locked loop according to an embodiment of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of the present invention to facilitate a better understanding of the invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and with various variations and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0011] As indicated in the specification and claims of this invention, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0012] While this invention makes various references to certain modules in systems according to embodiments of the invention, any number of different modules can be used and run on user terminals and / or servers. The modules are merely illustrative, and different aspects of the systems and methods may use different modules.

[0013] This invention uses flowcharts to illustrate the operations performed by the system according to embodiments of the invention. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, various steps can be processed in reverse order or simultaneously, as needed. Furthermore, other operations can be added to these processes, or one or more steps can be removed from them.

[0014] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0015] In the technical solution of this invention, a method for synchronizing wind power converters with weak grids based on injection phase-locked loops is proposed. Figure 1 This is a flowchart of a wind power converter weak grid synchronization method based on an injection phase-locked loop according to an embodiment of the present invention. Figure 2 This is a schematic diagram of data flow in a wind power converter weak grid synchronization method based on an injection phase-locked loop according to an embodiment of the present invention. (In conjunction with...) Figure 1 and Figure 2 According to an embodiment of the present invention, a wind power converter weak grid synchronization method based on injection phase-locked loop includes the following steps: S1, injecting disturbance signals into the d-axis current reference signal and q-axis current reference signal corresponding to the wind power converter and performing data acquisition to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter; S2, performing frequency domain data transformation and disturbance response extraction on the original three-phase voltage at the PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum; S3, performing grid impedance calculation on the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum to obtain the grid impedance matrix spectrum; S4, performing stability margin assessment and injection parameter decision on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain the optimized injection amplitude and the optimized injection frequency; S5, performing adaptive injection phase-locking based on the optimized injection amplitude and the optimized injection frequency to obtain the phase-locked loop output phase and the phase-locked loop output frequency.

[0016] Specifically, in step S1, a disturbance signal is injected into the d-axis and q-axis current reference signals corresponding to the wind power converter, and data acquisition is performed to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter. It should be understood that grid impedance cannot be directly measured; it must be indirectly calculated by analyzing the voltage and current response relationship of the system under disturbance. Therefore, this step actively and purposefully excites the system by injecting a carefully designed broadband disturbance signal into the current control loop of the wind power converter, causing it to generate small fluctuations at multiple frequency points. The original data of the voltage at the point of common coupling (PCC) and the output current of the converter are collected at this moment to obtain the system's response to this series of known excitations. This original data is the key input for subsequent frequency domain analysis, disturbance response extraction, and calculation of the grid impedance matrix spectrum, providing an essential data foundation for the final realization of adaptive phase-locked loop.

[0017] The disturbance signal specifically refers to a d-axis digital disturbance current sequence (PRBS) signal, also known as a pseudo-random binary sequence. PRBS exhibits white noise characteristics in its spectrum, meaning its energy is uniformly distributed over a wide frequency range. This makes it an ideal disturbance source, capable of simultaneously exciting the system's response at multiple frequency points, significantly improving identification efficiency. The d-axis and q-axis current reference signals are the current command values ​​of the converter's internal control system in the dq synchronous rotating coordinate system. In typical wind power converter control strategies, the d-axis current is usually used to control active power or DC bus voltage, while the q-axis current is used to control reactive power or AC voltage amplitude. These reference signals are the control targets of the inner current loop. The PCC point, or point of common coupling, refers to the electrical node connecting the wind power generation system (including the converter) to the main power grid. The voltage and current at the PCC point are key physical quantities characterizing the interaction between the converter and the grid.

[0018] In its specific implementation, S1 first generates a d-axis digital perturbation current sequence based on the PRBS order, perturbation clock frequency, and perturbation amplitude. During this process, a pseudo-random binary sequence is constructed according to preset parameters. The PRBS order determines the sequence length and spectral resolution; the perturbation clock frequency determines the symbol rate of the sequence, indirectly affecting the bandwidth of the perturbation signal; and the perturbation amplitude controls the magnitude of the injected perturbation, ensuring that it generates a sufficiently strong response for measurement without significantly impacting the normal operation of the power grid.

[0019] Next, the d-axis digital disturbance current sequence and the d-axis current reference signal are superimposed with d-axis commands to obtain the final d-axis current command, and the q-axis current reference signal is used as the final q-axis current command. Both the final d-axis and final q-axis current commands are sent to the inner current loop. The inner current loop refers to the innermost and fastest-responding control loop in the converter control system. Its responsibility is to accurately and quickly track the d-axis and q-axis current commands, control the switching action of the inverter bridge, and thus generate the desired output current. In this process, the d-axis digital disturbance current sequence generated in the previous step is added to the d-axis current reference signal required for normal converter operation, forming a new final d-axis current command with slight fluctuations. It is worth noting that the disturbance is only applied to the d-axis, while the q-axis current reference signal is not superimposed and is directly used as the final q-axis current command. These two final current commands are jointly sent to the converter's inner current loop as its latest control target.

[0020] Furthermore, the raw three-phase voltage at the PCC point and the raw three-phase current of the converter are acquired by voltage transformers and current transformers installed at the PCC point and the AC output side of the converter. In other words, the measurement equipment deployed at the hardware level begins operation simultaneously with the injection of disturbance signals into the power system. The voltage transformer (PT) installed at the PCC point and the current transformer (CT) installed on the AC output side of the converter measure the three-phase voltage and three-phase current waveforms in the circuit in real time with high precision. These unprocessed, continuous analog signals containing disturbance responses are sampled and converted from analog to digital to form a digital time series of the raw three-phase voltage at the PCC point and the raw three-phase current of the converter, which is then stored for subsequent analysis and processing.

[0021] Specifically, S2 involves performing frequency domain data transformation and disturbance response extraction on the original three-phase voltage at the PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. It should be understood that the original voltage and current data are time-domain signals that not only contain disturbance components but also mix the fundamental operating components of the power grid (e.g., a 50Hz or 60Hz sine wave), inherent system harmonics, and various background noises. If analyzed directly in the time domain, these different components are superimposed and extremely difficult to separate. Since the power grid impedance is a frequency-varying parameter, it must be analyzed in the frequency domain. Therefore, in the technical solution of this invention, the signal is mapped from the time domain to the frequency domain using mathematical tools of frequency domain transformation, allowing the signal components of different frequencies to be separated and displayed. Then, through precise extraction, clean voltage and current spectra corresponding only to the injected disturbance are obtained, thereby realizing the transformation from raw data to effective information.

[0022] In its specific implementation, S2 firstly involves performing a Fast Fourier Transform (FFT) and full-spectrum calculation on the original three-phase voltage at the PCC point and the original three-phase current of the converter to obtain the full spectrum of the PCC voltage dq and the converter current dq. During this process, firstly, the acquired original three-phase voltage at the PCC point and the original three-phase current of the converter are transformed from a three-phase stationary coordinate system (abc) to a synchronous rotating coordinate system (dq). This is typically achieved through the Park transform, the purpose of which is to decouple the AC signal into a DC component (representing the fundamental frequency) and an AC component (representing harmonics and disturbances) for easier subsequent analysis. Secondly, after completing the coordinate transformation, the controller performs a Fast Fourier Transform (FFT) on the four sets of time-domain data obtained, thereby calculating their respective full spectra to obtain the full spectrum of the PCC voltage dq and the converter current dq. It is worth mentioning that the Fast Fourier Transform (FFT) is an efficient algorithm for calculating the Discrete Fourier Transform (DFT). It can decompose a digital signal in the time domain into a series of sinusoidal components of different frequencies and provide the amplitude and phase information of each component. It is the core tool for signal processing to shift from time domain to frequency domain analysis.

[0023] Furthermore, based on the perturbation frequency list, the perturbation response at key frequency points is precisely extracted from the full spectrum of PCC voltage (dq) and converter current (dq) to obtain the dq-axis voltage perturbation spectrum and dq-axis current perturbation spectrum. During this process, a pre-generated perturbation frequency list matching the injected PRBS signal is used to index and filter the full spectrum data obtained in the previous step. The perturbation frequency list is a pre-defined set of frequencies. Since the perturbation signal (such as PRBS) is generated by the controller itself, its spectral characteristics are known; therefore, the perturbation frequency list contains all valid perturbation frequencies, providing an index for subsequent precise extraction. Specifically, the controller iterates through each frequency value in this list and then precisely finds and reads the complex values ​​(including amplitude and phase) corresponding to these specific frequency points in the full spectrum of PCC voltage (dq) and converter current (dq). Spectral data at all non-perturbation frequency points are ignored. Through this operation, the system simplifies the massive full-spectrum information into a series of voltage and current response values ​​at specific perturbation frequency points, ultimately obtaining the dq-axis voltage perturbation spectrum and the dq-axis current perturbation spectrum.

[0024] Specifically, in step S3, the grid impedance is calculated on the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum to obtain the grid impedance matrix spectrum. It should be understood that grid impedance, as a key parameter in the equivalent Thevenin circuit of the grid, is an inherent physical property describing how the grid responds to current disturbances (i.e., what kind of voltage fluctuations are generated). It does not change with the operating state of the converter and is an inherent characteristic of the grid. By calculating the grid impedance matrix at various frequency points, the overall picture of the grid can be accurately depicted. This accurate grid model is the basis for subsequent system stability analysis, margin assessment, and adaptive control parameter tuning.

[0025] In its specific implementation, S3 first calculates the voltage response matrix and current response matrix based on the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. To determine the four unknown elements in a two-row, two-column grid impedance matrix, sufficient response data must be obtained through at least two independent current disturbance experiments. Each disturbance experiment generates a set of d-axis voltage response, q-axis voltage response, d-axis current disturbance, and q-axis current disturbance at a specified frequency. Specifically, for each frequency f in the disturbance frequency list, the controller performs the following steps.

[0026] First, data collection and organization: utilizing dq-axis voltage perturbation spectrum and dq-axis current perturbation spectrum data obtained from two or more independent perturbation experiments. For example, suppose a d-axis current reference perturbation experiment was conducted (obtaining one set of response data, denoted as "1") and a q-axis current reference perturbation experiment was conducted (obtaining another set of response data, denoted as "2").

[0027] Next, the voltage response matrix is ​​formed: the d-axis voltage perturbation components and q-axis voltage perturbation components obtained in the first perturbation experiment at frequency f are used as the first column of the matrix; the d-axis voltage perturbation components and q-axis voltage perturbation components obtained in the second perturbation experiment at frequency f are used as the second column of the matrix, thus constructing the voltage response matrix.

[0028] Then, the current response matrix is ​​formed: in the same way, the d-axis current perturbation component and the q-axis current perturbation component obtained at frequency f in the first perturbation experiment are used as the first column of the current response matrix; the d-axis current perturbation component and the q-axis current perturbation component obtained at frequency f in the second perturbation experiment are used as the second column of the current response matrix, thus constructing the current response matrix.

[0029] Furthermore, based on the voltage response matrix and the current response matrix, the spectrum of the grid impedance matrix is ​​calculated. That is, after constructing the voltage response matrix and the current response matrix, matrix operations are used to solve for the grid impedance matrix. According to the voltage-current relationship of the grid, the voltage response matrix and the current response matrix satisfy the following matrix equation: Furthermore, the power grid impedance matrix can be calculated from this equation. The specific steps are as follows: First, perform an inversion operation on the current response matrix to obtain its inverse matrix. Then, multiply the obtained inverse matrix by the voltage response matrix from the right side. .

[0030] Specifically, S4 involves evaluating the stability margin and deciding on injection parameters for the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and frequency. It should be understood that in weak grid environments, the complexity and dynamic changes in grid impedance can lead to resonance or instability between the wind power converter and the grid. By evaluating the current system's stability margin in real time, potential instability can be predicted in advance. Secondly, the operating parameters and structure of the grid are constantly changing, and traditional fixed-parameter injection phase-locked loops are difficult to adapt to this dynamic environment. By continuously evaluating the stability margin and dynamically adjusting the amplitude and frequency of disturbance injection accordingly, the system can always probe with optimized parameters, ensuring measurement accuracy while avoiding the impact of excessive disturbances on system operation. Ultimately, this provides a decision-making basis for achieving efficient, safe, and reliable synchronization of the wind power converter under various weak grid conditions.

[0031] Among them, stability margin is an indicator of the system's stability. Injection amplitude refers to the magnitude of the disturbance signal injected into the d-axis current reference signal; its optimization aims to minimize interference to the power grid while ensuring stable system detection. Injection frequency refers to the main frequency components of the injected disturbance signal; its optimization aims to select the frequency point that most effectively reflects the key dynamic characteristics of the power grid, or to adjust to the safest and most effective detection frequency range under different operating conditions.

[0032] In its specific implementation, S4 first calculates the current phase margin based on the grid impedance matrix spectrum and the converter's equivalent impedance matrix. During this process, the converter's equivalent impedance matrix is ​​inverted to obtain the converter's equivalent admittance matrix. The converter's equivalent impedance matrix describes the relationship between the current flowing through the converter and the resulting voltage drop. To analyze the system's open-loop characteristics, it needs to be converted into admittance form; the admittance matrix is ​​the inverse of the impedance matrix.

[0033] Next, the grid impedance matrix spectrum is multiplied by the converter equivalent admittance matrix to obtain the open-loop return ratio matrix. The grid and converter form a feedback loop, and its open-loop characteristics determine the system stability. Here, the grid impedance matrix is ​​multiplied by the converter equivalent admittance matrix to obtain the open-loop return ratio matrix.

[0034] Furthermore, Bode plot analysis is performed on the open-loop return ratio matrix to obtain the scalar loop gain and crossover frequency. For multiple-input multiple-output (MIMO) systems, directly applying the Bode plot concept of SISO systems requires certain transformations. In the technical solution of this invention, a scalar loop gain that reflects the overall stability of the system is extracted from the open-loop return ratio matrix. This can be achieved by analyzing the singular values, eigenvalues, or determinants of the open-loop return ratio matrix. By plotting a Bode plot (gain-frequency plot and phase-frequency plot) on this scalar gain, the crossover frequency can be found, which is the frequency corresponding to the amplitude of the scalar loop gain being 1 (0 dB).

[0035] Subsequently, the phase of the scalar loop gain at the crossover frequency is read, and the current phase margin is determined based on this phase. That is, after determining the crossover frequency, the corresponding phase angle at that frequency is read from the phase curve of the Bode plot; then, the current phase margin is calculated according to the standard definition in control theory. This process can be expressed by the following formula: ; in, In order to cross frequencies scalar loop gain The phase; Next, an injection amplitude decision is made based on the current phase margin, target phase margin, previous cycle injection amplitude, and outer loop control cycle to obtain an optimized injection amplitude. This step aims to dynamically adjust the amplitude of the injected disturbance to maintain the system operating within a safe stability margin range. In this process, firstly, the margin error between the current phase margin and the target phase margin is calculated. Specifically, the current phase margin... The error value is calculated by comparing it with the preset target phase margin.

[0036] Next, the margin error is input into the discrete PI controller to obtain the PI controller output. In the technical solution of this invention, in order to smoothly and accurately adjust the injection amplitude, the aforementioned margin error is... The input is fed into a discrete proportional-integral (PI) controller. The PI controller generates a control output term based on the current error and the accumulated error to reduce the phase margin error.

[0037] Furthermore, the PI controller output is subjected to saturation limiting to obtain an optimized injection amplitude. Considering that the PI controller output may exceed a reasonable range, in order to protect the equipment and avoid excessive disturbance, the output is further subjected to saturation limiting to between a preset minimum and maximum injection amplitude, thereby obtaining an optimized injection amplitude.

[0038] Furthermore, an injection frequency decision is made based on the search frequency range of the grid impedance matrix spectrum to obtain an optimized injection frequency. This step aims to select the most suitable frequency for disturbance injection to efficiently and accurately acquire grid information. During this process, the controller analyzes the characteristics of the grid impedance matrix spectrum within a preset search frequency range. The selection criteria for the optimized injection frequency include: selecting the frequency point where the grid impedance characteristics change most significantly, or selecting the frequency point that has the most significant impact on system stability, so as to more sensitively capture changes in the grid. In another embodiment of the invention, the frequency point that performs best in evaluating stability margin can be selected by traversing a set of preset frequencies. This strategy ensures that the disturbance injection is always performed at a frequency that maximizes information acquisition efficiency and identification accuracy, thereby obtaining an optimized injection frequency.

[0039] Specifically, in step S5, adaptive injection-type phase-locked loop (PLL) is performed based on optimized injection amplitude and frequency to obtain the PLL output phase and frequency. It should be understood that traditional PLLs (such as voltage-based PLLs) suffer severe performance degradation, even leading to lockout, in weak power grids due to problems such as PCC point voltage distortion, high harmonic content, and large frequency fluctuations. Injection-type PLLs, by actively injecting a disturbance signal of known frequency and amplitude into the power grid and analyzing the grid's response to the disturbance signal, indirectly obtain the grid's phase information, greatly improving anti-interference capability and synchronization accuracy under harsh power grid conditions. Secondly, by adaptively adjusting the PLL through optimized injection amplitude and frequency, optimal efficiency and safety can be achieved while ensuring synchronization performance. Specifically, optimized injection amplitude ensures that the signal can be effectively identified in complex power grid environments, while avoiding unnecessary impact on the power grid itself due to excessive disturbances. Optimized injection frequency ensures that the disturbance can efficiently excite the power grid and be detected at the frequency point that best reflects the dynamic characteristics of the power grid, thereby improving the PLL's response speed and accuracy. This adaptive mechanism enables the entire synchronization method to dynamically adapt to changes in power grid conditions and always maintain optimal operating conditions.

[0040] Adaptive injection phase-locked loops (PLLs) are a special type of PLL that not only actively injects disturbance signals to detect the power grid, but also adaptively adjusts its injection parameters (i.e., optimized injection amplitude and frequency) based on the real-time conditions of the power grid (obtained through previous steps of grid impedance and stability information) to continuously optimize synchronization performance. Unlike fixed-parameter injection PLLs, it exhibits stronger environmental adaptability. The PLL output phase represents the instantaneous phase angle of the fundamental voltage of the power grid. It serves as the reference for synchronization operations in the converter's internal control system (such as dq coordinate transformation and PWM modulation). Accurate phase information is crucial for controlling the converter output current to be in phase with or at a specific phase difference from the grid voltage. The PLL output frequency represents the instantaneous angular frequency of the fundamental voltage of the power grid. It can be obtained by differentiating the output phase. Accurate frequency information plays a decisive role in maintaining frequency consistency between the converter and the power grid and preventing drift.

[0041] In specific implementation, S5 first generates a disturbance signal based on the optimized injection amplitude and frequency, and injects it into the d-axis current reference signal and the q-axis current reference signal. The PLL transforms the three-phase AC quantities of the power grid into the dq rotating coordinate system using the current estimated phase provided by its internal oscillator. Subsequently, based on the optimized injection amplitude and frequency, a disturbance component (such as a sinusoidal disturbance) is constructed and superimposed on the d-axis current reference signal. Typically, this disturbance is generated internally by the PLL and superimposed on the current current command.

[0042] Next, the three-phase voltage and converter three-phase current at the PCC point are acquired and converted into voltage and current signals in the dq domain. During this process, the PLL needs to extract the response components corresponding to the optimized injection frequency from these signals in real time. This can be achieved by employing real-time Fourier transform processing, such as Discrete Fourier Transform (DFT), lock-in amplifier principles, or techniques based on notch filters, to accurately analyze the amplitude and phase information of the voltage and current responses at the injection frequency.

[0043] Next, phase detection is performed to generate a phase error signal. In this process, the PLL compares the grid phase estimated internally with the actual phase information observed through the injected signal response. Specifically, it analyzes the phase of the voltage or current response component (typically represented as an AC component in the dq coordinate system) caused by the optimized injected frequency disturbance and compares it with the reference phase output by the internal oscillator. This comparison generates a phase error signal, representing the deviation between the PLL's currently estimated phase and the actual grid phase. Specifically, based on the grid impedance matrix at the injected frequency, the converter equivalent impedance matrix, and the feedback from the PLL, the voltage response phase that the injected disturbance should produce under the current phase estimate is calculated; the difference between the theoretical phase and the actually measured response phase is the phase error.

[0044] The phase error signal is then processed through a loop filter. During this process, the generated phase error signal is input into a loop filter (typically a proportional-integral (PI) controller). The loop filter smooths the error signal, suppresses noise, and generates an adjustment signal according to the control law. The output of the PI controller is used to adjust the frequency and phase of the PLL's internal oscillator, ensuring the system stably and quickly tracks the power grid.

[0045] Finally, the voltage-controlled oscillator (VCO) or digitally controlled oscillator (NCO) integrates the correction values ​​to output the final phase and frequency of the phase-locked loop (PLL). The output of the loop filter serves as the input to the VCO or NCO to adjust its oscillation frequency. The VCO / NCO integrates this adjustment signal and superimposes it with a nominal frequency (such as the rated frequency of the power grid) to output the PLL output frequency in real time; then, by integrating this instantaneous angular frequency, the PLL output phase is obtained.

[0046] In summary, the wind power converter weak grid synchronization method based on injection-type phase-locked loop (PLL) according to embodiments of the present invention is explained. It actively injects a disturbance signal into the grid and analyzes the resulting voltage and current responses in real time, thereby accurately quantifying the currently unknown grid impedance characteristics. Based on this measured data, the current stability margin can be accurately assessed, and the optimal amplitude and frequency of the injected signal can be dynamically determined. In this way, it can be ensured that the wind power converter can always adaptively maintain the system in an optimal state with sufficient stability margin when facing any unknown and dynamically changing weak grid environment, thereby eliminating the risk of synchronization instability oscillations and significantly improving grid robustness and power quality.

[0047] This invention also provides a wind power converter weak grid synchronization system based on an injection phase-locked loop.

[0048] Figure 3This is a block diagram of a wind power converter weak grid synchronization system based on an injection-type phase-locked loop according to an embodiment of the present invention. Figure 3 As shown, the wind power converter weak grid synchronization system 300 based on injection phase-locked loop according to an embodiment of the present invention includes: a data acquisition module 310, used to inject disturbance signals into the d-axis current reference signal and q-axis current reference signal corresponding to the wind power converter and perform data acquisition to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter; and a disturbance response extraction module 320, used to perform frequency domain data transformation and disturbance response extraction on the original three-phase voltage at the PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance. The system includes: a grid impedance calculation module 330, used to calculate the grid impedance from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum to obtain the grid impedance matrix spectrum; an injection parameter decision module 340, used to evaluate the stability margin and make injection parameter decisions from the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency; and an adaptive injection phase-locked loop module 350, used to perform adaptive injection phase-locking based on optimized injection amplitude and optimized injection frequency to obtain the phase-locked loop output phase and phase-locked loop output frequency.

[0049] The specific implementation method of the wind power converter weak grid synchronization system based on injection phase-locked loop provided in this embodiment of the invention can be found in the wind power converter weak grid synchronization method based on injection phase-locked loop provided in this embodiment of the invention, and will not be repeated here.

[0050] The wind power converter weak grid synchronization system 300 based on injection phase-locked loop (PLL) according to embodiments of the present invention can be implemented in various wireless terminals, such as servers with a wind power converter weak grid synchronization algorithm based on injection PLL. In one possible implementation, the wind power converter weak grid synchronization system 300 based on injection PLL according to embodiments of the present invention can be integrated into the wireless terminal as a software module and / or a hardware module. For example, the wind power converter weak grid synchronization system 300 based on injection PLL can be a software module in the operating system of the wireless terminal, or it can be an application developed for the wireless terminal; of course, the wind power converter weak grid synchronization system 300 based on injection PLL can also be one of many hardware modules of the wireless terminal.

[0051] Alternatively, in another example, the wind power converter weak grid synchronization system 300 based on injection phase-locked loop and the wireless terminal can also be separate devices, and the wind power converter weak grid synchronization system 300 based on injection phase-locked loop can be connected to the wireless terminal via wired and / or wireless networks, and transmit interactive information in accordance with an agreed data format.

[0052] Those skilled in the art will understand that the above embodiments are specific implementations of the present invention, and in practical applications, various changes can be made in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A method for synchronizing a wind power converter with a weak grid based on an injection phase-locked loop, characterized in that, include: The disturbance signal is injected into the d-axis current reference signal and q-axis current reference signal of the wind power converter and data is collected to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter. Frequency domain data transformation and disturbance response extraction are performed on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. The grid impedance matrix spectrum is obtained by calculating the grid impedance matrix spectrum from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. Stability margin assessment and injection parameter decision-making are performed on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency. Adaptive injection phase-locked loop (PLL) is performed based on optimized injection amplitude and optimized injection frequency to obtain the PLL output phase and PLL output frequency.

2. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 1, characterized in that, The disturbance signal is injected into the corresponding d-axis current reference signal and q-axis current reference signal of the wind power converter, and data acquisition is performed to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter, including: Based on the PRBS order, perturbation clock frequency, and perturbation amplitude, a d-axis digital perturbation current sequence is generated; The d-axis digital disturbance current sequence and the d-axis current reference signal are superimposed with d-axis commands to obtain the final d-axis current command, and the q-axis current reference signal is used as the final q-axis current command. The final d-axis current command and the final q-axis current command are sent to the inner current loop. The original three-phase voltage at the PCC point and the original three-phase current of the converter are collected by voltage transformers and current transformers installed at the PCC point and the AC output side of the converter.

3. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 1, characterized in that, Frequency domain data transformation and disturbance response extraction are performed on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum, including: Fast Fourier transform and full spectrum calculation are performed on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the full spectrum of PCC voltage dq and the full spectrum of converter current dq. Based on the disturbance frequency list, the perturbation response at key frequency points is accurately extracted for the full spectrum of PCC voltage dq and the full spectrum of converter current dq to obtain the dq-axis voltage perturbation spectrum and the dq-axis current perturbation spectrum.

4. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 1, characterized in that, The grid impedance matrix spectrum is obtained by calculating the grid impedance matrix from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum, including: Calculate the voltage response matrix and current response matrix based on the dq-axis voltage perturbation spectrum and the dq-axis current perturbation spectrum; The spectrum of the power grid impedance matrix is ​​calculated based on the voltage response matrix and the current response matrix.

5. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 1, characterized in that, Stability margin assessment and injection parameter decision-making are performed on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency, including: Calculate the current phase margin based on the grid impedance matrix spectrum and the converter equivalent impedance matrix; The injection amplitude is determined based on the current phase margin, the target phase margin, the injection amplitude of the previous cycle, and the outer loop control cycle to obtain an optimized injection amplitude. The optimal injection frequency is obtained by making an injection frequency decision based on the power grid impedance matrix spectrum within the search frequency range.

6. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 5, characterized in that, Based on the grid impedance matrix spectrum and the converter equivalent impedance matrix, the current phase margin is calculated, including: The equivalent impedance matrix of the converter is inverted to obtain the equivalent admittance matrix of the converter. The open-loop return ratio matrix is ​​obtained by multiplying the grid impedance matrix spectrum with the converter equivalent admittance matrix. Bode plot analysis of the open-loop return ratio matrix was performed to obtain the scalar loop gain and crossover frequency. Read the phase of the scalar loop gain at the cross-frequency and determine the current phase margin based on that phase.

7. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 6, characterized in that, Read the phase of the scalar loop gain at the cross-frequency and determine the current phase margin based on that phase, including: determining the current phase margin using the following formula: ； in, In order to cross frequencies scalar loop gain phase, This represents the current phase margin.

8. The method for synchronizing wind power converters with weak grids based on injection-type phase-locked loops according to claim 5, characterized in that, The injection amplitude is determined based on the current phase margin, target phase margin, previous cycle injection amplitude, and outer loop control cycle to obtain an optimized injection amplitude, including: Calculate the margin error between the current phase margin and the target phase margin; Input the margin error into the discrete PI controller to obtain the PI controller output; The PI controller output is saturated and limited to obtain an optimized injection amplitude.

9. A wind power converter weak grid synchronization system based on an injection phase-locked loop, characterized in that, include: The data acquisition module is used to inject disturbance signals into the d-axis current reference signal and q-axis current reference signal corresponding to the wind power converter and to acquire data to obtain the original three-phase voltage at the PCC point and the original three-phase current of the converter. The disturbance response extraction module is used to perform frequency domain data transformation and disturbance response extraction on the original three-phase voltage at PCC point and the original three-phase current of the converter to obtain the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum. The grid impedance calculation module is used to calculate the grid impedance from the dq-axis voltage disturbance spectrum and the dq-axis current disturbance spectrum to obtain the grid impedance matrix spectrum. The injection parameter decision module is used to perform stability margin assessment and injection parameter decision on the grid impedance matrix spectrum and the converter equivalent impedance matrix to obtain optimized injection amplitude and optimized injection frequency. An adaptive injection phase-locked loop (PLL) module is used to perform adaptive injection phase-locking based on optimized injection amplitude and optimized injection frequency to obtain the PLL output phase and PLL output frequency.

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