A method, system, device and medium for suppressing oscillation of a grid-forming converter system

Abstract

The present application relates to the technical field of grid-forming converter system, and particularly relates to a grid-forming converter system oscillation suppression method, system, device and medium, comprising: extracting harmonic components of grid-connected voltage and grid-connected current in real time through a sliding window discrete Fourier transform (SWDFT) algorithm; detecting the amplitude of the oscillation component in the harmonic component, and extracting the amplitude of the oscillation component causing the system oscillation frequency through an amplitude discriminant; when the amplitude discriminant is satisfied, calculating a harmonic impedance angle according to the harmonic voltage in the harmonic component and the corresponding harmonic current; adjusting the harmonic impedance angle through closed-loop control, so that the harmonic impedance angle is maintained at a target impedance angle value; adjusting the compensation current size of different harmonic components according to the adjusted harmonic impedance angle, to realize the tuning of the adaptive resonant filter; the system oscillation risk can be detected in real time, the filter parameters can be dynamically adjusted, the impedance of the multi-frequency converter can be remodeled, and the stability and reliability can be improved.

Description

Technical Field

[0001] This invention relates to the field of grid-type converter system technology, and in particular to a method, system, device and medium for oscillation suppression in a grid-type converter system. Background Technology

[0002] With the rapid development of new energy power generation technologies, the scenarios for new energy grid connection are increasing. As the electrification of the power system deepens, the power system is steadily moving towards a "dual-high" model of high proportion of new energy power generation and high proportion of power computer equipment. Grid-Forming (GFM) converters, due to their ability to actively provide voltage and frequency support, are gradually becoming an important component of new energy grid connection equipment.

[0003] However, grid-connected converters exhibit strong voltage source characteristics. Their complex multi-loop control structures, including droop control and virtual synchronous generator control, are highly susceptible to introducing negative damping in specific frequency bands when interacting with and coupling with weak grids or complex line impedances. This can induce broadband oscillations at low frequencies, sub-synchronous / super-synchronous frequencies, and even mid-to-high frequencies. Broadband oscillations dominated by grid-connected converters not only severely impact equipment and system safety but also further threaten grid security.

[0004] Current research on oscillation suppression in grid-type systems primarily focuses on the control level, employing additional control methods and optimized control parameters. Active damping control is commonly used in additional control, reshaping the impedance characteristics of the grid-type converter to be less prone to oscillations through the introduction of a controller. However, most additional damping controls rely on high-order, high-precision system models, and increasing the order of matrix calculations significantly increases the computational complexity of the control algorithm. Optimizing control parameters can be achieved through automatic tuning using algorithms such as particle swarm optimization. However, these tunings often do not address oscillation frequencies updated in real time. For grid-type converter systems where impedance characteristics vary with operating conditions, oscillation detection and suppression across multiple time scales need to be considered.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method, system, device and medium for oscillation suppression of grid-type converter systems, which can detect the oscillation risk of the system in real time, dynamically adjust the filter parameters and realize the impedance reshaping of multi-band converters, so as to improve the stability and reliability of the system.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a method for suppressing oscillations in a grid-type converter system, comprising the following steps: Harmonic components of grid-connected voltage and grid-connected current are extracted in real time using the sliding window discrete Fourier transform (SWDFT) algorithm. The amplitude of the oscillation component in the harmonic components is detected, and the amplitude of the oscillation component at the system oscillation frequency is extracted using an amplitude discriminant. The oscillation component includes voltage. and current ; When the amplitude discrimination formula is satisfied, the harmonic impedance angle is calculated based on the harmonic voltage and the corresponding subharmonic current in the harmonic component. The harmonic impedance angle is adjusted by closed-loop control to maintain the harmonic impedance angle at the target impedance angle value; Based on the adjusted harmonic impedance angle, the magnitude of the compensation current for different harmonic components is adjusted to achieve the tuning of the adaptive resonant filter.

[0008] Furthermore, the sliding window SWDFT algorithm includes: The grid-connected voltage and grid-connected current are sampled at a preset sampling period; At each sampling time, the real and imaginary parts of each harmonic are calculated based on the sampled values ​​within the current sampling window; The amplitude and phase of each harmonic component are calculated based on the real and imaginary parts.

[0009] Furthermore, the sampling of grid-connected voltage and grid-connected current at a preset sampling period includes the following steps: For grid-connected voltage Current Sampling is performed to obtain a discrete sequence of the continuous signal. (n=0, 1, 2...), determine the window length and sliding step size ,N≫M; Create a circular buffer to store the most recent data. One sampling point; Each time received When a new sampling point is added, the previous ones will be used. Discard the data from each sampling point and store the new data at the end of the buffer. exist Execution A SWDFT at points can yield frequencies of Quantity in Frequency domain vector at time step The expression is updated to: ; in The frequency domain vector at time n-1, for A discrete sequence of time points.

[0010] Furthermore, the amplitude discriminant is expressed in the following form: ; In the formula, Indicates the voltage in the harmonic components amplitude or current Amplitude; Voltage amplitude threshold or current amplitude threshold used to determine whether oscillation has occurred.

[0011] Furthermore, the oscillation determination threshold It is 5% of the fundamental frequency amplitude.

[0012] Furthermore, the harmonic impedance angle is calculated based on the harmonic voltage and corresponding subharmonic current in the harmonic components. This includes the following steps: Obtain the harmonic voltage amplitude and phase of the target subharmonic; Obtain the harmonic current amplitude and phase of the target subharmonic; The harmonic impedance angle is calculated based on the difference between the phase of the harmonic voltage and the phase of the harmonic current.

[0013] Furthermore, the closed-loop control equation for the tunable harmonic impedance angle adaptive tunable filter is established as follows: ; In the formula, This represents the tuning coefficient of the compensation current; for The proportional gain of the PI controller at time 1. for The first moment One harmonic impedance angle This represents the initial value of the integral coefficient of the PI controller; The norm of the impedance angle is used to characterize the intensity of oscillation. When the oscillation is strong, an adaptive adjustment coefficient can be used. Adjust the scaling factor; The integral coefficient of the PI controller; The impedance angle reference value is set to 0.

[0014] Furthermore, adjusting the compensation current magnitude for different harmonic components based on the adjusted harmonic impedance angle includes the following steps: Calculate the required compensation current amplitude for each harmonic based on the adjusted harmonic impedance angle. Determine the phase of the compensation current for each harmonic; A compensation current control signal is generated and applied to the adaptive resonant filter.

[0015] Furthermore, the first The magnitude of the compensation current for each harmonic component Obtained from the following formula: ; In the formula, Represents the harmonic compensation coefficient. Indicates the first One harmonic current amplitude.

[0016] Furthermore, the adaptive resonant filter can be tuned by controlling the inductance of the main winding through a controlled current source, as expressed in the following expression: ; In the formula, The equivalent impedance of the adaptive tunable filter. The equivalent resistance of the main winding of the adaptive tunable filter. For complex frequency domain operators, This is the equivalent capacitance of the main winding of the adaptive tunable filter. The equivalent inductance of the main winding of the adaptive tunable filter. To account for the compensation inductance referred to the main winding, The mutual inductance values ​​of the coupled inductors. For harmonic compensation coefficients, The system impedance before compensation. The impedance of the compensated grid-type converter system.

[0017] The present invention also provides an oscillation suppression system for a grid-type converter system, comprising: The harmonic extraction module is used to extract the harmonic components of grid-connected voltage and grid-connected current in real time using the sliding window SWDFT algorithm; An oscillation determination module is used to detect the amplitude of the oscillation component in the harmonic components and determine whether the amplitude of the oscillation component reaches a preset oscillation determination threshold. The impedance angle calculation module is used to calculate the harmonic impedance angle based on the harmonic voltage and the corresponding subharmonic current in the harmonic component when the amplitude of the oscillation component reaches the oscillation determination threshold. The impedance angle control module is used to adjust the harmonic impedance angle through closed-loop control, so that the harmonic impedance angle is maintained at the target impedance angle value. The compensation current adjustment module is used to adjust the magnitude of the compensation current for different harmonic components according to the adjusted harmonic impedance angle. An adaptive resonant filter is used to generate a compensation current based on the output of the compensation current adjustment module and apply it to the converter system.

[0018] Furthermore, the adaptive resonant filter includes: A multi-channel harmonic current generator is used to generate compensation currents for each harmonic. Current amplitude regulator, used to adjust the amplitude of the compensation current of each channel; Current phase adjuster, used to adjust the phase of the compensation current in each channel; The filter parameter self-tuning unit is used to automatically adjust the filter parameters according to the changes in the harmonic impedance angle.

[0019] Furthermore, it also includes a system status monitoring module, which is used to determine whether the system is in a steady state and output a response speed adjustment signal to the impedance angle control module.

[0020] The present invention also provides a computer device, including a processor and a memory, wherein the memory stores a computer program, and the computer program, when executed by the processor, implements the oscillation suppression method for a grid-type converter system as described above.

[0021] The present invention also provides a computer-readable storage medium, wherein the computer program stored therein, when executed by a processor, implements the oscillation suppression method for a grid-type converter system as described above.

[0022] The beneficial effects of this invention are as follows: This invention identifies the main harmonic components within a sliding window range in real time and updates the active equivalent reactance of the filter in real time through the control loop, ensuring that the system can still operate stably at multiple time scales; moreover, this method uses only one LC filter branch and suppresses multiple harmonic components through an active tuned reactor, which can reduce the cost of the filter device. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, 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 recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the oscillation suppression method for a grid-type converter system in an embodiment of the present invention. Figure 2 This is a flowchart illustrating the oscillation suppression process for a grid-type converter system in an embodiment of the present invention. Figure 3This is a schematic diagram of the control loop for oscillation suppression in a grid-type converter system according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the oscillation suppression system of the grid-type converter system in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of a computer device in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly attached to the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] like Figures 1 to 3 The oscillation suppression method for the grid-type converter system shown includes: Harmonic components of grid-connected voltage and grid-connected current are extracted in real time using the sliding window discrete Fourier transform (SWDFT) algorithm. The amplitude of the oscillating component in the harmonic components is detected, and the amplitude of the oscillating component at the system oscillation frequency is extracted using an amplitude discriminant. The oscillating component includes voltage. and current ; When the amplitude discriminant is satisfied, the harmonic impedance angle is calculated based on the harmonic voltage and the corresponding subharmonic current in the harmonic component. The harmonic impedance angle is adjusted by closed-loop control to maintain the harmonic impedance angle at the target impedance angle value; Based on the adjusted harmonic impedance angle, the magnitude of the compensation current for different harmonic components is adjusted to achieve the tuning of the adaptive resonant filter.

[0029] Specifically, the first step involves real-time extraction of harmonic components. In this step, the control unit continuously acquires the instantaneous values ​​of the three-phase voltage and three-phase current at the grid connection point at a fixed sampling frequency. The sampled data is then processed using a sliding window discrete Fourier transform algorithm. Specifically, the system maintains a data window that stores the most recent several periods of sampled data in chronological order. Whenever a new sampled value arrives, the window slides forward by a fixed step, discarding the oldest data at the beginning of the window and adding the new data to the end. Then, a discrete Fourier transform is performed on all sampled values ​​within the window to calculate the real and imaginary parts of each harmonic, thereby obtaining the amplitude and phase of each harmonic. This sliding window mechanism ensures continuous updating of harmonic information and enables real-time tracking of the dynamic changes in harmonic components in the grid-connected voltage and current.

[0030] After obtaining the real-time harmonic components, the system enters the oscillation component detection and discrimination step. This step identifies the amplitude of all frequency components from the extracted harmonic components and uses an amplitude discriminant to screen out the risk components that are truly causing system oscillations. The basic principle of this amplitude discriminant is to compare the amplitude of a certain harmonic voltage or harmonic current with a preset threshold. Only when the amplitude exceeds the threshold is the voltage or current at that frequency determined as an oscillation component that needs to be suppressed. In a preferred embodiment, this threshold is set as a relative value related to the fundamental frequency amplitude, so that the discrimination rule can adapt to fundamental frequency changes under different operating conditions. Through this discriminant, the system can accurately pinpoint the critical frequency currently causing system oscillations.

[0031] When the above amplitude discrimination condition is met, the system immediately triggers the harmonic impedance angle calculation step. For each harmonic component marked as the target oscillation frequency, this step uses the harmonic voltage and harmonic current information at the same frequency to calculate the harmonic impedance angle at that frequency point. In a preferred implementation, the system extracts the phase of the harmonic voltage and the phase of the harmonic current from the results of the sliding window discrete Fourier transform, respectively. The difference between the voltage phase and the current phase is obtained, and this difference is defined as the harmonic impedance angle at that frequency. The magnitude and sign of this angle directly reflect the impedance characteristics of the grid-type converter at that frequency, and are the core basis for judging the oscillation risk and guiding subsequent suppression measures.

[0032] After obtaining the harmonic impedance angle, this method actively adjusts this angle through closed-loop control to maintain it near the preset target impedance angle value. In this closed-loop control step, the system compares the calculated actual harmonic impedance angle with the target value to obtain the angle deviation, and then sends this deviation signal to a closed-loop regulator. The regulator outputs a corresponding control quantity based on the magnitude and direction of the deviation. This control quantity does not directly change the impedance angle itself, but indirectly adjusts the compensation current of the filter through subsequent steps, thereby changing the equivalent impedance of the converter at that frequency. The closed-loop regulator typically includes an integral term to ensure that the angle deviation can be completely eliminated in steady state, achieving zero steady-state error regulation. In addition, the regulator's response speed can be appropriately adjusted according to the severity of the current oscillation, thereby achieving a balance between rapidly suppressing oscillation and avoiding over-regulation.

[0033] Finally, based on the harmonic impedance angle adjusted by closed-loop control, the system executes the steps of adjusting the compensation current and tuning the adaptive resonant filter. For each oscillation frequency that needs to be suppressed, this step first determines the required amplitude and phase of the compensation current at that frequency based on the adjusted harmonic impedance angle: the greater the deviation of the harmonic impedance angle from the target value, the greater the required amplitude of the compensation current; the phase of the compensation current must be matched with the phase of the original harmonic current and the current impedance angle deviation, so that the injected compensation current can effectively change the impedance characteristics of the filter. After calculating the compensation current commands for each harmonic, the system sends these commands to the adaptive resonant filter. This filter has parameter self-tuning capability and can automatically adjust its internal equivalent inductance, capacitance, or resistance parameters according to the received compensation current commands, thereby shifting its resonant characteristics and achieving dynamic tracking and suppression of specific oscillation frequencies. Through the cyclic execution of the above five steps, the system can detect oscillation risks in real time over a wide frequency range, dynamically adjust filter parameters, and ultimately reshape the impedance characteristics of the grid converter into a form that is not prone to oscillation.

[0034] This invention identifies the main harmonic components within a sliding window range in real time and updates the active equivalent reactance of the filter in real time through a control loop, ensuring stable operation of the system across multiple time scales. Furthermore, this method uses only one LC filter branch and suppresses multiple harmonic components through an active tuned reactor, thereby reducing the cost of the filtering device.

[0035] Based on the above embodiments, the sliding window SWDFT algorithm includes: The grid-connected voltage and grid-connected current are sampled at a preset sampling period; At each sampling time, the real and imaginary parts of each harmonic are calculated based on the sampled values ​​within the current sampling window; The amplitude and phase of each harmonic component are calculated based on the real and imaginary parts.

[0036] Specifically, the grid-connected voltage and grid-connected current are sampled at a preset sampling period. This sampling period can be set according to the actual harmonic analysis requirements. For example, in the case of a power frequency of 50 Hz, 128 or 256 points are sampled per cycle, corresponding to sampling periods of 156.25 microseconds and 78.125 microseconds, respectively. The sampled discrete data is stored in a buffer in chronological order for subsequent processing. Next, at each sampling moment, the real and imaginary parts of each harmonic are calculated based on all sampled values ​​stored in the current sampling window. Here, the length of the sampling window is fixed at several complete fundamental cycles, such as one or two cycles. For each target harmonic order, the value of each sampling point within the window is multiplied by the corresponding cosine and sine function values, and the products are accumulated. The accumulated result is the real and imaginary parts of that harmonic. Finally, based on the calculated real and imaginary parts, the amplitude of each harmonic is obtained through square root operations, and the phase of each harmonic is obtained through arctangent operations. The quadrant of the phase is determined based on the signs of the real and imaginary parts. These three steps are repeated at each sampling moment, thus providing real-time updated harmonic information for subsequent oscillation amplitude determination and impedance angle calculation.

[0037] Based on the above embodiments, the grid-connected voltage and grid-connected current are sampled at a preset sampling period, including the following steps: For grid-connected voltage Current Sampling is performed to obtain a discrete sequence of the continuous signal. (n=0, 1, 2...), determine the window length and sliding step size ,N≫M; Create a circular buffer to store the most recent data. One sampling point; Each time received When a new sampling point is added, the previous ones will be used. Discard the data from each sampling point and store the new data at the end of the buffer. exist Execution A SWDFT at points can yield frequencies of Quantity in Frequency domain vector at time step The expression is updated to: ; in The frequency domain vector at time n-1, for A discrete sequence of time points.

[0038] Specifically, firstly, the grid-connected voltage and current are continuously sampled to obtain a discrete sequence, where n represents the sampling time number. The window length N and sliding step M are determined, with N being much larger than M. For example, in a 50 Hz power frequency scenario, N can be set to 1024 points and M to 128 points, ensuring that the sliding step is much smaller than the window length each time. Then, a circular buffer is established in memory specifically to store the most recent N sampling points. This buffer is organized chronologically, with new data continuously overwriting the oldest data. Each time M new sampling points are received, the first M oldest sampling points in the buffer are discarded, and these M new sampling points are stored at the end of the buffer, thus completing the window sliding. Next, after each sliding step, a discrete Fourier transform is performed on all N points in the buffer. To reduce computation, a recursive method is used to update the frequency domain vector: for the component with frequency index k, its frequency domain vector at the current time n is equal to the frequency domain vector at the previous time multiplied by a rotation factor, plus the contribution of the current new sampling point, and minus the contribution of the removed oldest sampling point. The above recursive process avoids recalculating all N points of the SWDFT after each slide, significantly improving the algorithm's real-time performance. In this way, a set of updated harmonic frequency domain vectors can be obtained for each sliding step, providing continuous and efficient frequency domain information for subsequent oscillation detection.

[0039] Based on the above embodiments, the amplitude discriminant is expressed as follows: ; In the formula, Represents the voltage in the harmonic components amplitude or current Amplitude; Voltage amplitude threshold or current amplitude threshold used to determine whether oscillation has occurred.

[0040] Specifically, let the amplitude of a certain harmonic voltage extracted from the sliding window SWDFT algorithm be... The corresponding subharmonic current amplitude is Simultaneously, two thresholds are preset: a voltage oscillation detection threshold and a current oscillation detection threshold. The amplitude discriminant is expressed as follows: when the voltage amplitude of a certain harmonic... The voltage threshold or the current amplitude of that harmonic is greater than the voltage threshold. When the current exceeds the threshold, a harmful oscillation component is determined to exist at that frequency and needs to be suppressed. Here, the voltage and current thresholds can be fixed absolute values ​​or relative values ​​related to the fundamental frequency amplitude. After each sliding window SWDFT calculation, the voltage amplitude of each harmonic is sequentially compared with... Comparison, current amplitude and Upon comparison, once the discriminant condition is met, the system records the voltage and current amplitudes at that oscillation frequency and triggers subsequent harmonic impedance angle calculation steps. This amplitude discriminant effectively filters out inherent minor harmonic interference during normal operation and accurately pinpoints the oscillation frequency that needs active suppression.

[0041] Based on the above embodiments, the oscillation determination threshold It is 5% of the fundamental frequency amplitude.

[0042] Based on the above embodiments, the harmonic impedance angle is calculated according to the harmonic voltage and corresponding subharmonic current in the harmonic components. This includes the following steps: Obtain the harmonic voltage amplitude and phase of the target subharmonic; Obtain the harmonic current amplitude and phase of the target subharmonic; The harmonic impedance angle is calculated based on the difference between the phase of the harmonic voltage and the phase of the harmonic current.

[0043] Specifically, the harmonic voltage amplitude and phase of the target subharmonic are obtained from the real-time updates of the sliding window SWDFT algorithm. For example, the target subharmonic is 150 Hz, i.e., the 3rd harmonic. Specifically, at the frequency corresponding to this subharmonic, the amplitude and phase calculation results of the voltage channel are read, with the phase typically using the fundamental zero-crossing point as a reference. Secondly, similarly from the results of the sliding window SWDFT algorithm, the harmonic current amplitude and phase of the target subharmonic are obtained, and the amplitude and phase information of the current channel at this frequency are read. Finally, the harmonic impedance angle is calculated based on the difference between the harmonic voltage phase and the harmonic current phase; that is, the harmonic voltage phase minus the harmonic current phase, and the resulting difference is the harmonic impedance angle at that frequency. For example, if the phase of a harmonic voltage is 30 degrees and the phase of a harmonic current is 10 degrees, then the harmonic impedance angle is 20 degrees, indicating that the current lags behind the voltage at this frequency, and the system exhibits inductive behavior. If the phase of the harmonic voltage is 30 degrees and the phase of the harmonic current is 50 degrees, then the harmonic impedance angle is -20 degrees, indicating that the system exhibits capacitive behavior. The magnitude and sign of this angle directly reflect the impedance characteristics of the grid-type converter at that oscillation frequency, providing a crucial basis for subsequent closed-loop control adjustments. The above three steps are executed independently for each marked oscillation frequency to obtain the harmonic impedance angle corresponding to each frequency point.

[0044] Based on the above embodiments, the closed-loop control equation of the tunable impedance angle adaptive tunable filter is established as follows: ; In the formula, This represents the tuning coefficient of the compensation current; for The proportional gain of the PI controller at time 1. for The first moment One harmonic impedance angle This represents the initial value of the integral coefficient of the PI controller; The norm of the impedance angle is used to characterize the intensity of oscillation. When the oscillation is strong, an adaptive adjustment coefficient can be used. Adjust the scaling factor; The integral coefficient of the PI controller; The impedance angle reference value is set to 0.

[0045] Specifically, the impedance angle reference value is set to zero degrees, aiming to achieve optimal damping by ensuring the system exhibits purely resistive characteristics at this oscillation frequency. The measured impedance angle of the i-th harmonic at the current moment is compared with the reference value to obtain the angle deviation. The proportional-integral controller outputs a compensation current tuning coefficient based on this deviation. The proportional coefficient is not fixed but adaptively adjusted according to the intensity of the current oscillation: a norm of the impedance angle is introduced to characterize the intensity of the oscillation. This norm can be, for example, the sum of the absolute values ​​of the impedance angles of each harmonic or the root mean square value. When the oscillation is strong, the norm of the impedance angle is large. In this case, an adaptive adjustment coefficient amplifies the proportional coefficient, enabling the controller to output a stronger regulating action to quickly suppress the oscillation. When the oscillation is weak, the proportional coefficient returns to its initial value to avoid over-adjustment. The integral coefficient remains fixed to eliminate steady-state angular error. The output of the proportional-integral controller is the compensation current tuning coefficient, which is directly used to adjust the magnitude of the compensation current for different harmonic components. Through the above closed-loop control equations, the harmonic impedance angle is monitored in real time and actively adjusted to keep it near zero degrees, thereby ensuring that the converter system always maintains positive damping characteristics at this oscillation frequency.

[0046] Based on the above embodiments, the compensation current for different harmonic components is adjusted according to the adjusted harmonic impedance angle, including the following steps: Calculate the required compensation current amplitude for each harmonic based on the adjusted harmonic impedance angle. Determine the phase of the compensation current for each harmonic; A compensation current control signal is generated and applied to the adaptive resonant filter.

[0047] Specifically, based on the harmonic impedance angle adjusted by closed-loop control, the required compensation current amplitude for each harmonic is calculated. Specifically, for each oscillation frequency marked as needing suppression, the magnitude of the compensation current amplitude is positively correlated with the degree to which the current harmonic impedance angle deviates from the target value: the greater the deviation of the harmonic impedance angle from zero, the more severe the oscillation at that frequency, and the greater the required compensation current amplitude; conversely, when the harmonic impedance angle is close to zero, the compensation current amplitude decreases. In a preferred implementation, the compensation current amplitude can be obtained by multiplying the original harmonic current amplitude by a tuning coefficient output by closed-loop control, which monotonically changes with the harmonic impedance angle deviation; secondly, the phase of the compensation current for each harmonic is determined. The phase of the compensation current needs to be such that its injection effectively changes the filter's impedance characteristics, thereby pulling the harmonic impedance angle towards zero. Typically, the phase of the compensation current is related to the phase of the original harmonic current and the current harmonic impedance angle. The basic principle is to ensure that the additional voltage generated by the compensation current can cancel out the voltage component that causes oscillations. In a specific example, if the measured harmonic impedance angle is positive, indicating that the system is inductive, the phase of the compensation current should be appropriately led to introduce a capacitive effect for cancellation. Finally, based on the calculated amplitude and phase of the compensation current for each harmonic, a corresponding compensation current control signal is generated and applied to the adaptive resonant filter. This control signal is typically a pulse-width modulated waveform, driving the controlled current source in the filter to output the actual compensation current according to the command. These three steps are executed in parallel for each oscillation frequency that needs to be suppressed, ensuring that the adaptive resonant filter can dynamically compensate for oscillation components in multiple frequency bands simultaneously.

[0048] Based on the above embodiments, the first The magnitude of the compensation current for each harmonic component Obtained from the following formula: ; In the formula, Represents the harmonic compensation coefficient. Indicates the first One harmonic current amplitude.

[0049] Specifically, for each oscillation frequency that needs to be suppressed, the magnitude of the compensation current is obtained by multiplying the original current magnitude of that harmonic by a harmonic compensation coefficient. This harmonic compensation coefficient is not a fixed constant but is dynamically determined by the aforementioned closed-loop control based on the deviation of the current harmonic impedance angle. Specifically, when the compensation current tuning coefficient output by the closed-loop controller is large, the harmonic compensation coefficient is correspondingly larger, increasing the ratio of the compensation current magnitude to the original harmonic current magnitude, thus providing stronger damping. When the harmonic impedance angle is close to the target value of zero degrees, the harmonic compensation coefficient decreases, reducing the compensation current magnitude and avoiding overcompensation. Through this multiplicative relationship, the compensation current magnitude maintains a linear proportion to the original harmonic current magnitude, ensuring sufficient suppression while avoiding excessive compensation current that could burden the system. This calculation formula is applicable to harmonic components of any order, and the compensation coefficients corresponding to each harmonic can be adjusted independently, thereby achieving multi-band adaptive compensation.

[0050] Based on the above embodiments, the inductance of the main winding can be controlled by a controlled current source to achieve the tuning of the adaptive resonant filter, as expressed in the following expression: ; In the formula, The equivalent impedance of the adaptive tunable filter. The equivalent resistance of the main winding of the adaptive tunable filter. For complex frequency domain operators, This is the equivalent capacitance of the main winding of the adaptive tunable filter. The equivalent inductance of the main winding of the adaptive tunable filter. To account for the compensation inductance referred to the main winding, The mutual inductance values ​​of the coupled inductors. For harmonic compensation coefficients, The system impedance before compensation. The impedance of the compensated grid-type converter system.

[0051] Specifically, to suppress oscillations across multiple frequency bands simultaneously with a single filter branch, this filter employs a structure where a main winding is connected to a controlled current source via a coupling inductor. By adjusting the magnitude and phase of the output current from the controlled current source, the equivalent compensation inductance referred to the main winding side can be altered, thereby dynamically adjusting the filter's resonant characteristics. Specifically, the equivalent impedance of the adaptive tunable filter is determined by the equivalent resistance, equivalent capacitance, and equivalent inductance of the main winding, as well as the compensation inductance referred to the main winding. The compensation inductance referred to the main winding is equal to the mutual inductance of the coupling inductor multiplied by the harmonic compensation coefficient. Since the harmonic compensation coefficient dynamically changes with the deviation of the harmonic impedance angle, the compensation inductance is also continuously adjustable. When the harmonic compensation coefficient increases, the compensation inductance increases, and the inductive component in the equivalent impedance changes accordingly, causing the filter's resonant point to shift to a lower frequency; when the harmonic compensation coefficient decreases, the resonant point shifts to a higher frequency. The impedance of the grid-type converter system before compensation is combined with the equivalent impedance of the filter in parallel or series to obtain the total impedance of the compensated system. Through the above tuning mechanism, the filter can track the changes in oscillation frequency in real time and automatically adjust the equivalent impedance to a state that makes the harmonic impedance angle approach zero degrees, thereby achieving adaptive suppression of oscillations in multiple frequency bands with a single filter branch.

[0052] like Figure 4 As shown, the present invention also provides an oscillation suppression system for a grid-type converter system, comprising: The harmonic extraction module is used to extract the harmonic components of grid-connected voltage and grid-connected current in real time using the sliding window SWDFT algorithm; The oscillation determination module is used to detect the amplitude of the oscillation component in the harmonic components and determine whether the amplitude of the oscillation component reaches the preset oscillation determination threshold. The impedance angle calculation module is used to calculate the harmonic impedance angle based on the harmonic voltage and the corresponding subharmonic current in the harmonic component when the amplitude of the oscillation component reaches the oscillation judgment threshold. The impedance angle control module is used to adjust the harmonic impedance angle through closed-loop control, so that the harmonic impedance angle is maintained at the target impedance angle value. The compensation current adjustment module is used to adjust the magnitude of the compensation current for different harmonic components according to the adjusted harmonic impedance angle. An adaptive resonant filter is used to generate a compensation current based on the output of the compensation current adjustment module and apply it to the converter system.

[0053] Specifically, the system comprises six functional modules that work together to detect and suppress oscillations in real time. The harmonic extraction module uses a sliding window discrete Fourier transform algorithm to continuously sample and analyze the voltage and current at the grid connection point, outputting the amplitude and phase information of each harmonic in real time. The oscillation determination module receives the output from the harmonic extraction module, detects the amplitude of the oscillation component in each harmonic, and compares this amplitude with a pre-set oscillation determination threshold. Once the voltage or current amplitude of a harmonic reaches or exceeds the threshold, it is determined that harmful oscillation exists at that frequency. The impedance angle calculation module starts after the oscillation determination module is triggered. For the marked oscillation frequency, it obtains the phase information of the voltage and current of the corresponding harmonic from the harmonic extraction module, and calculates the harmonic impedance angle at that frequency by calculating the difference between the voltage phase and the current phase. The angle control module employs a closed-loop control strategy, comparing the measured harmonic impedance angle with the target impedance angle value. Based on the deviation, it outputs an adjustment amount, which is used to change the magnitude of the subsequent compensation current, thereby dynamically maintaining the harmonic impedance angle near the target value. The compensation current adjustment module, based on the adjustment amount output by the impedance angle control module and combined with the original current amplitude of each harmonic, determines the required compensation current amplitude and phase for each frequency to be suppressed, and generates corresponding control commands. The adaptive resonant filter receives the commands from the compensation current adjustment module and, through its internal controlled current source and coupled inductor structure, generates a compensation current in real time and injects it into the converter system, thereby effectively changing the filter's impedance characteristics and achieving adaptive suppression of oscillations across multiple frequency bands. These six modules constitute a complete closed-loop control system, capable of responding to oscillation changes in real time without relying on a precise system model, effectively improving the stability and reliability of the grid-type converter system.

[0054] Based on the above embodiments, the adaptive resonant filter includes: A multi-channel harmonic current generator is used to generate compensation currents for each harmonic. Current amplitude regulator, used to adjust the amplitude of the compensation current of each channel; Current phase adjuster, used to adjust the phase of the compensation current in each channel; The filter parameter self-tuning unit is used to automatically adjust the filter parameters according to the changes in the harmonic impedance angle.

[0055] Specifically, the adaptive resonant filter comprises four cooperating components. A multi-channel harmonic current generator generates compensation currents for each harmonic, internally providing an independent current generation channel for each oscillation frequency to be suppressed. Each channel can independently output a sinusoidal current at that frequency, and the outputs of all channels are superimposed at a summing node and injected into the converter system. A current amplitude regulator adjusts the amplitude of the compensation current in each channel, receiving amplitude commands from the compensation current adjustment module and independently controlling the current amplitude of each channel. A current phase regulator adjusts the phase of the compensation current in each channel, also receiving phase commands from the compensation current adjustment module and independently controlling the current phase of each channel. A filter parameter self-tuning unit automatically adjusts the filter parameters based on changes in the harmonic impedance angle. It monitors the dynamic changes in the harmonic impedance angle during closed-loop control in real time and accordingly changes the operating point of the internal coupling inductor or the capacitance value of the variable capacitor, thereby enabling the resonant frequency of the entire filter to adaptively shift with the oscillation frequency. The four components work closely together: the multi-channel harmonic current generator provides the hardware foundation; the current amplitude regulator and current phase regulator perform precise control of amplitude and phase, respectively; and the filter parameter self-tuning unit adjusts the inherent characteristics of the filter at a more fundamental level, thereby jointly realizing the adaptive resonant filter's dynamic suppression function for broadband oscillations. Based on the above embodiment, a system state monitoring module is also included to determine whether the system is in a steady state and to output a response speed adjustment signal to the impedance angle control module.

[0056] like Figure 5 As shown, the present invention also provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program. When the computer program is executed by the processor 410, it implements the above-mentioned method for suppressing oscillations in a grid-connected converter system, including the following steps: extracting the harmonic components of the grid-connected voltage and grid-connected current in real time using a sliding window discrete Fourier transform (SWDFT) algorithm; detecting the amplitude of the oscillation component in the harmonic components, and extracting the amplitude of the oscillation component at the frequency causing the system oscillation using an amplitude discriminant. The oscillation component includes voltage. and current When the amplitude discrimination formula is satisfied, the harmonic impedance angle is calculated based on the harmonic voltage and corresponding subharmonic current in the harmonic components; the harmonic impedance angle is adjusted by closed-loop control to maintain the harmonic impedance angle at the target impedance angle value; based on the adjusted harmonic impedance angle, the compensation current of different harmonic components is adjusted to achieve the tuning of the adaptive resonant filter.

[0057] The present invention also provides a computer-readable storage medium 430, wherein the computer program stored therein, when executed by a processor 410, implements the above-described method for suppressing oscillations in a grid-connected converter system, comprising the following steps: extracting harmonic components of grid-connected voltage and grid-connected current in real time using a sliding window discrete Fourier transform (SWDFT) algorithm; detecting the amplitude of the oscillation component in the harmonic components, and extracting the amplitude of the oscillation component at the frequency causing system oscillation using an amplitude discriminant, wherein the oscillation component includes voltage. and current When the amplitude discrimination formula is satisfied, the harmonic impedance angle is calculated based on the harmonic voltage and corresponding subharmonic current in the harmonic components; the harmonic impedance angle is adjusted by closed-loop control to maintain the harmonic impedance angle at the target impedance angle value; based on the adjusted harmonic impedance angle, the compensation current of different harmonic components is adjusted to achieve the tuning of the adaptive resonant filter.

[0058] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0061] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0062] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0063] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0064] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0065] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for suppressing oscillations in a grid-type converter system, characterized in that, Includes the following steps: Harmonic components of grid-connected voltage and grid-connected current are extracted in real time using the sliding window discrete Fourier transform (SWDFT) algorithm. The amplitude of the oscillation component in the harmonic components is detected, and the amplitude of the oscillation component at the system oscillation frequency is extracted using an amplitude discriminant. The oscillation component includes voltage. and current ; When the amplitude discrimination formula is satisfied, the harmonic impedance angle is calculated based on the harmonic voltage and the corresponding subharmonic current in the harmonic component. The harmonic impedance angle is adjusted by closed-loop control to maintain the harmonic impedance angle at the target impedance angle value; Based on the adjusted harmonic impedance angle, the magnitude of the compensation current for different harmonic components is adjusted to achieve the tuning of the adaptive resonant filter.

2. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The sliding window SWDFT algorithm includes: The grid-connected voltage and grid-connected current are sampled at a preset sampling period; At each sampling time, the real and imaginary parts of each harmonic are calculated based on the sampled values ​​within the current sampling window; The amplitude and phase of each harmonic component are calculated based on the real and imaginary parts.

3. The oscillation suppression method for a grid-type converter system according to claim 2, characterized in that, The sampling of grid-connected voltage and grid-connected current at a preset sampling period includes the following steps: For grid-connected voltage Current Sampling is performed to obtain a discrete sequence of the continuous signal. (n=0, 1, 2...), determine the window length and sliding step size ,N≫M; Create a circular buffer to store the most recent data. One sampling point; Each time received When a new sampling point is added, the previous ones will be used. Discard the data from each sampling point and store the new data at the end of the buffer. exist Execution A SWDFT at points can yield frequencies of Quantity in Frequency domain vector at time step The expression is updated to: ； in The frequency domain vector at time n-1, for A discrete sequence of time points.

4. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The amplitude discriminant is expressed in the following form: ； In the formula, Indicates the voltage in the harmonic components amplitude or current Amplitude; Voltage amplitude threshold or current amplitude threshold used to determine whether oscillation has occurred.

5. The oscillation suppression method for a grid-type converter system according to claim 4, characterized in that, The oscillation determination threshold It is 5% of the fundamental frequency amplitude.

6. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The harmonic impedance angle is calculated based on the harmonic voltage and corresponding subharmonic current in the harmonic components. This includes the following steps: Obtain the harmonic voltage amplitude and phase of the target subharmonic; Obtain the harmonic current amplitude and phase of the target subharmonic; The harmonic impedance angle is calculated based on the difference between the phase of the harmonic voltage and the phase of the harmonic current.

7. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The closed-loop control equation for the adaptive tunable filter with adjustable harmonic impedance angle is established as follows: ； In the formula, This represents the tuning coefficient of the compensation current; for The proportional gain of the PI controller at time 1. for The first moment One harmonic impedance angle This represents the initial value of the integral coefficient of the PI controller; The norm of the impedance angle is used to characterize the intensity of oscillation. When the oscillation is strong, an adaptive adjustment coefficient can be used. Adjust the scaling factor; The integral coefficient of the PI controller; The impedance angle reference value is set to 0.

8. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The step of adjusting the compensation current for different harmonic components based on the adjusted harmonic impedance angle includes the following steps: Calculate the required compensation current amplitude for each harmonic based on the adjusted harmonic impedance angle. Determine the phase of the compensation current for each harmonic; A compensation current control signal is generated and applied to the adaptive resonant filter.

9. The oscillation suppression method for a grid-type converter system according to claim 8, characterized in that, No. The magnitude of the compensation current for each harmonic component Obtained from the following formula: ； In the formula, Represents the harmonic compensation coefficient. Indicates the first One harmonic current amplitude.

10. The oscillation suppression method for a grid-type converter system according to claim 1, characterized in that, The adaptive resonant filter can be tuned by controlling the inductance of the main winding through a controlled current source, as expressed in the following expression: ； In the formula, The equivalent impedance of the adaptive tunable filter. The equivalent resistance of the main winding of the adaptive tunable filter. For complex frequency domain operators, This is the equivalent capacitance of the main winding of the adaptive tunable filter. The equivalent inductance of the main winding of the adaptive tunable filter. To account for the compensation inductance referred to the main winding, The mutual inductance values ​​of the coupled inductors. For harmonic compensation coefficients, The system impedance before compensation. The impedance of the compensated grid-type converter system.

11. An oscillation suppression system for a grid-type converter system, characterized in that, include: The harmonic extraction module is used to extract the harmonic components of grid-connected voltage and grid-connected current in real time using the sliding window SWDFT algorithm; An oscillation determination module is used to detect the amplitude of the oscillation component in the harmonic components and determine whether the amplitude of the oscillation component reaches a preset oscillation determination threshold. The impedance angle calculation module is used to calculate the harmonic impedance angle based on the harmonic voltage and the corresponding subharmonic current in the harmonic component when the amplitude of the oscillation component reaches the oscillation determination threshold. The impedance angle control module is used to adjust the harmonic impedance angle through closed-loop control, so that the harmonic impedance angle is maintained at the target impedance angle value. The compensation current adjustment module is used to adjust the magnitude of the compensation current for different harmonic components according to the adjusted harmonic impedance angle. An adaptive resonant filter is used to generate a compensation current based on the output of the compensation current adjustment module and apply it to the converter system.

12. The oscillation suppression system for a grid-type converter system according to claim 11, characterized in that, The adaptive resonant filter includes: A multi-channel harmonic current generator is used to generate compensation currents for each harmonic. Current amplitude regulator, used to adjust the amplitude of the compensation current of each channel; Current phase adjuster, used to adjust the phase of the compensation current in each channel; The filter parameter self-tuning unit is used to automatically adjust the filter parameters according to the changes in the harmonic impedance angle.

13. The oscillation suppression system for a grid-type converter system according to claim 11, characterized in that, It also includes a system status monitoring module, which is used to determine whether the system is in a steady state and output a response speed adjustment signal to the impedance angle control module.

14. A computer device comprising a processor and a memory, characterized in that, The memory stores a computer program that, when executed by the processor, implements the oscillation suppression method for a grid-type converter system as described in any one of claims 1 to 10.

15. A computer-readable storage medium, characterized in that, When the stored computer program is executed by the processor, it implements the oscillation suppression method for a grid-type converter system as described in any one of claims 1 to 10.

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