A preoscillation stability monitoring active damper for grid-connected power electronic systems

Abstract

The application discloses a pre-oscillation stability monitoring active damper for grid-connected power electronic systems and belongs to the technical field of power electronics. The pre-oscillation stability monitoring active damper comprises a direct-current voltage control loop stability energy storage, a stability monitoring loop, a wide-frequency pulse disturbance injection through phase-locked synchronization, grid impedance and inverter impedance based on fundamental wave separation and FFT calculation, an activation signal generated by using an MPC criterion, a virtual resistance started according to the activation signal, and a closed-loop optimization dynamic adjustment of the virtual resistance to make the system stability margin approach a critical value. The application realizes pre-oscillation intervention, solves the problems of response delay, high energy consumption and poor compatibility of traditional schemes, and simulation shows that the harmonic suppression response time is less than or equal to 20 ms and THD is reduced to 0.57%.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to an active damper for pre-oscillation stability monitoring in grid-connected power electronic systems. Background Technology

[0002] With the widespread application of renewable energy sources such as wind and solar power, power electronic devices such as grid-connected inverters have become an important component of modern power systems. However, the nonlinear characteristics of power electronic devices and their interaction with the power grid can easily lead to system stability problems under weak grid conditions, which not only reduces operational reliability but also affects grid security.

[0003] To address these issues, damping techniques stabilize the system by reshaping its impedance characteristics. See also... Figure 1 Traditional passive damping methods use passive components such as resistors, capacitors, or inductors. While these methods can suppress oscillations instantly and are simple and inexpensive to implement, their fixed damping characteristics and inherent energy losses limit their application in modern power electronic systems. Active damping methods construct virtual resistors through additional feedback control loops. Theoretically, they can suppress oscillations without physical energy loss and adapt to real-time changes in the power grid. However, they require modifications to the existing system control and are incompatible with third-party converters that lack open control interfaces.

[0004] Based on active damping methods, an active damper independent of existing power electronic systems has been proposed. Its external connection method allows it to adapt to most existing power electronic systems while ensuring active damping functionality. However, most existing active dampers operate in reactive mode, activating damping only when the harmonic amplitude exceeds the IEEE harmonic standard threshold. This delayed response leads to instability propagation in the system, increases total harmonic distortion, and degrades power quality. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an active damper for pre-oscillation stability monitoring of grid-connected power electronic systems, which addresses the shortcomings of the prior art and solves the technical problems of response delay, excessive power loss due to reliance on fixed parameter settings, and poor compatibility with existing system controllers.

[0006] The present invention adopts the following technical solution:

[0007] An active damper for pre-oscillation stability monitoring in grid-connected power electronic systems, comprising:

[0008] The DC voltage control circuit is connected to a DC capacitor and is used to regulate the DC capacitor voltage to stabilize energy storage and feed excess energy back to the grid.

[0009] The stability monitoring circuit connects to the grid voltage and current signals at the input end and generates activation / deactivation signals at the output end.

[0010] The damping control loop receives the activation / deactivation signal at its input and generates a virtual resistance control signal at its output.

[0011] The stability monitoring loop includes:

[0012] The disturbance injection module outputs a periodic wideband pulse signal to the output of the active damper. Its injection phase is synchronized with the grid voltage through a phase-locked loop, thereby acquiring voltage and current time-domain response data in real time.

[0013] The impedance calculation module is connected to the grid voltage and current response signals at its input terminal. It calculates the grid impedance by separating the fundamental component and performing a fast Fourier transform. Z g With inverter impedance Z inv ;

[0014] The stability criterion module, based on the maximum peak value criterion, compares the minimum loop gain. T The trajectory deviates from the preset stable restricted area, triggering activation / deactivation signals;

[0015] The damping control loop includes:

[0016] The virtual resistance generation module generates an adaptive virtual resistance value based on the activation signal. R v Dynamically adjust the output impedance of the active damper Z ad ;

[0017] Closed-loop optimization module, real-time calculation of... Z ad New loop gain T* Through iterative adjustments R v make T* The trajectory approaches the set stability margin boundary.

[0018] Preferably, the acquired voltage and current time-domain response data are processed as follows:

[0019] First, the disturbance response is separated by subtracting the fundamental waveform. Then, the separated disturbance response is subjected to frequency domain analysis using FFT, and the system impedance is calculated based on the frequency domain information.

[0020] Preferably, the disturbance injection module outputs a set periodic pulse reference signal, the duration of a single pulse is 0.5%-5% of the power grid cycle, and the phase-locked loop maintains a fixed phase difference with the zero-crossing point of the power grid voltage at each injection moment.

[0021] Preferably, the impedance calculation module performs:

[0022] The fundamental waveform is subtracted from the time-domain response data to separate the disturbance response; a fast Fourier transform is performed on the separated disturbance response to obtain frequency-domain information; and the grid impedance is calculated based on the frequency-domain information. Z g With inverter impedance Z inv .

[0023] Preferably, in the stability criterion module, the stability forbidden zone is the minimum loop gain in the complex plane. T The corresponding Nyquist curve does not allow entry into this restricted area. When any part of the Nyquist curve enters this restricted area, it is determined that the system has a potential instability risk or insufficient stability margin.

[0024] Preferably, the initial virtual resistance generation module R v The value is 0.1~1Ω. When the stability margin is greater than the set threshold, the value is increased. R v When the stability margin is less than the set threshold, reduce... R v .

[0025] Preferably, the input of the phase-locked loop is connected to the grid voltage signal, and the output provides a phase synchronization clock signal to the disturbance injection module.

[0026] Preferably, the DC voltage control circuit includes:

[0027] Voltage sampling circuit to collect DC capacitor voltage;

[0028] The current tracking controller drives the full-bridge circuit to feed DC-side energy back to the grid.

[0029] Preferably, the hardware carriers of the stability monitoring loop and the damping control loop are digital signal processors (DSPs). The disturbance injection module outputs pulse signals through the PWM generator of the DSP, the impedance calculation module is executed through the FFT calculator built into the DSP, and the virtual resistance generation module is updated in real time through the floating-point unit of the DSP. R v .

[0030] Preferably, the active damper is electrically connected to the common coupling point of the power grid through an output interface circuit; the output interface circuit is used to filter out the switching frequency harmonics output by the power electronic converter and match the impedance characteristics between the damper and the power grid.

[0031] Compared with the prior art, the present invention has at least the following beneficial effects:

[0032] An active damper for pre-oscillation stability monitoring in grid-connected power electronic systems achieves pre-oscillation intervention through the coordinated operation of three core circuits, solving the response delay problem of traditional dampers; disturbance injection and real-time impedance calculation identify stability risks in advance and avoid harmonic propagation.

[0033] Furthermore, fundamental frequency separation and FFT processing eliminate fundamental frequency interference, improve impedance calculation accuracy, and frequency domain analysis accurately locates the resonant point.

[0034] Furthermore, narrow-pulse disturbance injection within a specific range (e.g., 0.5% to 5% of the grid cycle) is employed to ensure effective excitation of the system over a wide frequency range. Simultaneously, phase-locked loop synchronous zero-crossing technology is combined to effectively avoid phase drift and ensure the comparability and measurement accuracy of disturbance response data.

[0035] Furthermore, the three-step impedance calculation method simplifies the processing flow and reduces DSP computing power requirements by 30%.

[0036] Furthermore, the quantization stability threshold corresponding to a 6dB gain margin + 30° phase margin has a false trigger rate of <5%.

[0037] Furthermore, through virtual resistance closed-loop optimization and adaptive mechanism, the energy consumption of the active damper itself is significantly reduced. According to actual measurements, the energy consumption can be reduced by up to 57%.

[0038] In summary, this invention achieves pre-oscillation stability intervention and features a plug-and-play design, ensuring good compatibility with third-party converters. It eliminates the need for significant modifications to existing grid-connected equipment, thereby comprehensively improving the operational reliability and stability of grid-connected power electronic systems in weak grid environments.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This diagram illustrates the basic connection method of a traditional active damper in a power electronic system.

[0042] Figure 2 This is a control block diagram of the active damper proposed in this invention;

[0043] Figure 3This is a schematic diagram of the stability criterion (MPC) used in this invention;

[0044] Figure 4 This is a flowchart illustrating the operation of the stability monitoring loop and damping control loop in this invention.

[0045] Figure 5 The main circuit waveform and related fast Fourier analysis results of the grid-connected system without the active damper of this invention are shown in the figure.

[0046] Figure 6 The waveforms of the main circuit of the grid-connected system and the results of related fast Fourier analysis are shown in the figure when the active damper of the present invention is added.

[0047] Figure 7 This diagram illustrates the preventative intervention function achieved by the present invention after integrating the stability detection ring.

[0048] Figure 8 This diagram illustrates the process of adaptive adjustment of the virtual resistance value achieved by the present invention after integrating the damping control loop. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, 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 with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0051] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0052] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0053] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0054] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0055] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0056] This invention provides an active damper for pre-oscillation stability monitoring in grid-connected power electronic systems.

[0057] Please refer to the figure. The present invention provides an active damper for pre-oscillation stability monitoring in grid-connected power electronic systems, comprising the following core control loops:

[0058] 1) DC voltage control loop: This loop maintains stable energy storage by adjusting the voltage on the DC capacitor and ensures that excess energy of the active damper is fed back to the system, supporting the continuous operation of the active damper while ensuring no additional energy loss.

[0059] 2) Stability monitoring loop: Designed to continuously assess the dynamic stability of the system and ensure that the system always operates within a preset stability margin range. Compared with existing active dampers, this monitoring loop can achieve preventative stability monitoring and identify potential unstable regions in advance.

[0060] Therefore, when the damping control loop is not triggered, the monitoring loop will record the current. I ad The control is a periodic pulse signal containing wideband information. Its injection timing is synchronized with the grid voltage cycle through phase-locked loop (PLL) control to ensure that the injection phase of each disturbance remains consistent.

[0061] The acquired voltage and current time-domain response data are then processed:

[0062] First, the disturbance response is separated by subtracting the fundamental waveform. Then, the separated disturbance response is subjected to frequency domain analysis using FFT, and the system impedance is calculated based on the frequency domain information.

[0063] (1)

[0064] in, This indicates the frequency domain information contained in the disturbance response after separating the fundamental wave.

[0065] This process enables real-time monitoring of system impedance changes and uses the classic maximum peak value (MPC) criterion to determine whether the system is in a stable state and the stability margin boundary.

[0066] Figure 3 This is a schematic diagram of the MPC criterion. The light blue curve corresponds to the minimum loop gain. T Also known as the impedance ratio, it can be calculated by measuring the power grid impedance. Z g With inverter impedance Z inv The ratio is given as:

[0067] (2)

[0068] in, For the power grid impedance at frequency The complex value at this frequency reflects the power grid's impediment to the current at this frequency, and includes resistive and reactive components. The inverter impedance at frequency The complex value at this frequency typically refers to the equivalent input impedance of the inverter as seen from the grid side. It encompasses the dynamic characteristics of the inverter's internal circuitry and controllers (including filters, current loops, phase-locked loops, etc.) at this frequency. In impedance-based stability criteria, the ratio of these two impedances is usually examined, and the characteristics of this ratio determine the stability of the entire grid-connected system.

[0069] The shaded area surrounded by the dark blue curve is called the restricted zone—the region where there is a risk of instability for system operation. By properly adjusting the impedance design to keep the minimum loop gain trajectory outside the restricted zone, it is possible to ensure that the system always has sufficient gain margin and phase margin. When the grid impedance changes and the minimum loop gain trajectory enters the restricted zone, the stability monitoring loop will trigger and activate the damping control loop.

[0070] 3) Damping Control Loop: This loop adjusts its own output impedance characteristics, regulates the system impedance relationship, and prevents oscillations caused by system impedance mismatch. Once activated, the proposed active damper's damping control loop adjusts its external output impedance based on monitoring results from the stability monitoring loop, ensuring the minimum loop gain trajectory returns to outside the restricted area and guaranteeing system stability. It's important to note that the minimum loop gain at this point is no longer the impedance ratio between the grid and the inverter. T It is the ratio of the grid impedance to the impedance of the inverter's parallel active damper. T* .

[0071] (3)

[0072] Active damper impedance Z ad It consists of its own impedance and the virtual impedance brought about by the damping control loop.

[0073] When the damping control loop is activated, the virtual resistance of the damping control loop... R v The initial value is set to a small value to ensure sufficient damping effect.

[0074] Subsequently, the virtual resistance value will be adjusted based on the updated minimum loop gain. T* The results of the MPC criterion are updated in real time.

[0075] If the stability margin is too large, then increase it. R v ;

[0076] If the stability margin is too small, then reduce R v This ensures that the active damper maintains sufficient stability margin while minimizing energy loss.

[0077] Throughout the process, the stability monitoring loop runs continuously at fixed intervals. Once it detects that the original system has returned to a stable state, the monitoring loop sends a deactivation signal, stopping the damping control loop from operating.

[0078] Please see Figure 4 The working method of an active damper for pre-oscillation stability monitoring in a grid-connected power electronic system according to the present invention is as follows:

[0079] S1, the stability monitoring loop remains operational;

[0080] S101, Disturbance signal injection, setting the damper output current. I ad The reference value is a periodic pulse signal containing wideband frequency information, and its injection time is synchronized with the grid voltage cycle through phase-locked loop (PLL) control to ensure that the injection phase of each disturbance is consistent.

[0081] S102, Response Data Processing and Impedance Calculation: After each disturbance injection in step S101, the voltage and current time-domain response data are acquired immediately. The disturbance response is separated by subtracting the fundamental waveform. The frequency domain information is obtained by performing a Fast Fourier Transform (FFT) on the separated disturbance response. Based on this frequency domain information, the relevant inverter output impedance and grid impedance of the system are calculated.

[0082] S103. Stability Assessment and Triggering: The system-related impedances calculated in step S102 are analyzed using the improved stability criterion (MPC criterion) to determine whether the system maintains sufficient stability margin. The minimum loop gain is defined in the stability criterion. T (by grid impedance) Z g With inverter impedance Z inv (The ratio is used to derive the value), and a stability forbidden zone is defined on the complex plane based on the system's preset stability margin. When the minimum loop gain curve crosses the stability forbidden zone on the complex plane, it means that the system's stability margin is insufficient. At this time, the stability detection loop will send an activation signal, and the damping control loop S2 will be triggered to activate. When the stability test passes, the stability detection loop will send a deactivation signal, and the damping control loop S2 will be triggered to close.

[0083] S104. After waiting for a fixed time interval, repeat steps S101 to S103 to achieve continuous stability monitoring.

[0084] S2, Damping control loop triggered operation;

[0085] S201. Upon receiving the activation signal generated in step S103, the virtual resistance control loop is activated (the virtual resistance loop adds an extra reference value to the original current loop, making the device exhibit additional impedance characteristics; generally, a single virtual resistance mode is used), and the initial value of the virtual resistance is set. R v ;

[0086] S202. According to the initial value of the virtual resistance set in step S201. R v Calculate the output impedance of the external active damper at this time. Z ad ;

[0087] S203. Recalculate the new minimum loop gain using the improved stability criterion from step S103, taking into account the output impedance of the active damper. T* ;

[0088] S204, Use new T* Perform a stability margin determination. If the stability margin is insufficient, decrease the virtual resistance value; if the stability margin is excessive, increase the virtual resistance value.

[0089] S205. Substitute the increased or decreased virtual resistance value into step S202 to recalculate the output impedance of the active damper.

[0090] S206. Repeat steps S203 to S205 until the stability margin of the system is maintained at the set boundary in step S204 or a deactivation signal is received from the stability detection loop.

[0091] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0092] A single-phase grid-connected inverter system was simulated in MATLAB / Simulink, and the relevant simulation parameters are shown in the table below:

[0093] Table 1. Simulation Test Related Parameters

[0094]

[0095] This simulation was conducted under two operating conditions for comparative testing:

[0096] (1) Basic grid-connected system operating condition without active dampers;

[0097] (2) The grid-connected system operating condition that integrates the proposed active damper. Figure 5 and Figure 6 The performance of the grid-connected system under two different operating conditions was demonstrated when grid fluctuations occurred.

[0098] At t=0.2 seconds, a 50% step increase in grid impedance is introduced to simulate a change from a strong to a weak grid. The system's time-domain operation is then analyzed by monitoring the point of common coupling (PCC) voltage, inverter current, and grid current. Simultaneously, Fast Fourier Transform (FFT) analysis is used to perform frequency-domain analysis of the grid current to obtain the system's frequency-domain variations.

[0099] Combining the time-domain and frequency-domain analysis results, it can be seen that: Figure 5 In the basic grid-connected operating condition shown, the increase in grid impedance at 0.2s induces a 1350 Hz harmonic, which is gradually amplified thereafter. Subsequent FFT analysis at t=0.8s reveals severe harmonic distortion, with the 1350 Hz harmonic being the dominant component, accompanied by a nonlinear sideband region with ±250Hz intervals. At this point, the grid current THD reaches 10.31%.

[0100] And in Figure 6 In the integrated active damper operating condition shown, the grid impedance also increases at 0.2s. However, the stability monitoring loop detects the system impedance change within 20 milliseconds (t=0.22s), directly triggering the damping control loop. Subsequently, the addition of the damping control loop changes the system impedance, suppressing oscillations before they occur and maintaining the system's continuous stable operation. Similarly, the FFT analysis performed at t=0.8s shows that the 1350 Hz harmonic that should have appeared was completely eliminated, and the grid current THD dropped to 0.57%. The change from the basic grid-connected operating condition to the integrated active damper operating condition demonstrates that the addition of the active damper significantly improves system stability and power quality. Most importantly, the proposed active damper can be connected to the system as a "plug-and-play" device without modifying the original system's circuitry and control architecture.

[0101] In the above simulation comparison, the proposed pre-oscillation stability intervention mechanism of the active damper relies on real-time assessment of the system's stability state, such as... Figure 7As shown in the diagram, based on the principles described in Section 3, the system's real-time impedance is periodically acquired and imported into a stability criterion to obtain the system's stability state (as shown in the first sub-figure). When the system's stability state exceeds a preset stability margin threshold (-6 in the first sub-figure), the active damper activates damping control before significant oscillations occur (as shown in the third sub-figure). Simultaneously, the stability monitoring loop also captures potential resonant frequencies (as shown in the second sub-figure) and performs targeted compensation through the damping control loop. By combining online monitoring and a triggering mechanism based on the stability margin threshold, the proposed active damper not only achieves stability intervention before oscillations but also minimizes energy loss.

[0102] Figure 8 This demonstrates the self-optimization process of the virtual resistance value. By iteratively updating the output impedance of the damper and comparing it with a preset stability margin threshold, and then dynamically adjusting Rv through a closed-loop algorithm, the stability margin after the addition of the active damper is always maintained at the critical value. Compared with implementing a fixed virtual resistance value, this closed-loop adjustment method can ensure the best damping effect with lower power loss.

[0103] Simulation results show that under the condition of a 50% step change in grid impedance, the dominant harmonic of 1350Hz was successfully eliminated, reducing the grid current THD from 10.31% to 0.57%, and improving power quality by 18 times. Adaptive damping reduces energy consumption and keeps the system operating at the critical stability point.

[0104] In summary, this invention presents an active damper for pre-oscillation stability monitoring in grid-connected power electronic systems. Based on phase-locked synchronization and wideband pulse disturbance injection, combined with fundamental frequency separation and real-time FFT impedance calculation technology, it can accurately identify grid impedance changes within 20ms. By activating damping in advance through the MPC stability criterion, it blocks harmonic amplification paths at the source. Compared to a fixed virtual resistance scheme, energy consumption is reduced by more than 57%, solving the problem of ineffective losses caused by over-damping in traditional active dampers. An external LC filter is connected in parallel to the PCC point, requiring no modification to the original system control architecture. The full-bridge topology is compatible with a wide voltage range of 150Vdc / 70Vac, directly compatible with third-party converters, and suitable for weak grid scenarios such as wind power / photovoltaic power. Experiments verify that its monitoring-damping full-process response time is ≤20ms, which is 5 times faster than the traditional harmonic threshold triggering mode. This invention replaces post-event remediation with predictive stability intervention, overcomes the limitations of fixed parameters with dynamic energy consumption optimization, and achieves broad compatibility with hardware decoupling design, providing a low-loss, highly reliable stability guarantee solution for high-proportion renewable energy grid-connected systems.

[0105] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An active damper for pre-oscillation stability monitoring in grid-connected power electronic systems, characterized in that, include: The DC voltage control circuit is connected to a DC capacitor and is used to regulate the DC capacitor voltage to stabilize energy storage and feed excess energy back to the grid. The stability monitoring circuit connects to the grid voltage and current signals at the input end and generates activation / deactivation signals at the output end. The damping control loop receives the activation / deactivation signal at its input and generates a virtual resistance control signal at its output. The stability monitoring loop includes: The disturbance injection module outputs a periodic wideband pulse signal to the output of the active damper. Its injection phase is synchronized with the grid voltage through a phase-locked loop, thereby acquiring voltage and current time-domain response data in real time. The impedance calculation module is connected to the grid voltage and current response signals at its input terminal. It calculates the grid impedance by separating the fundamental component and performing a fast Fourier transform. Z g With inverter impedance Z inv ; The stability criterion module, based on the maximum peak value criterion, compares the minimum loop gain. T The trajectory deviates from the preset stable restricted area, triggering activation / deactivation signals; The damping control loop includes: The virtual resistance generation module generates an adaptive virtual resistance value based on the activation signal. R v Dynamically adjust the output impedance of the active damper Z ad ; Closed-loop optimization module, real-time calculation of... Z ad New loop gain T* Through iterative adjustments R v make T* The trajectory approaches the set stability margin boundary.

2. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The acquired voltage and current time-domain response data are processed as follows: First, the disturbance response is separated by subtracting the fundamental waveform. Then, the separated disturbance response is subjected to frequency domain analysis using FFT, and the system impedance is calculated based on the frequency domain information.

3. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The disturbance injection module outputs a set periodic pulse reference signal, the duration of which is 0.5%-5% of the grid cycle, and the phase-locked loop maintains a fixed phase difference with the grid voltage zero crossing point at each injection moment.

4. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, Impedance calculation module execution: The fundamental waveform is subtracted from the time-domain response data to separate the disturbance response; the frequency domain information is obtained by performing a fast Fourier transform on the separated disturbance response. Calculating power grid impedance based on frequency domain information Z g With inverter impedance Z inv .

5. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, In the stability criterion module, the stability forbidden zone is the minimum loop gain in the complex plane. T The corresponding Nyquist curve does not allow entry into this restricted area. When any part of the Nyquist curve enters this restricted area, it is determined that the system has a potential instability risk or insufficient stability margin.

6. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, Initialization of the virtual resistance generation module R v The value is 0.1~1Ω. When the stability margin is greater than the set threshold, the value is increased. R v When the stability margin is less than the set threshold, reduce... R v .

7. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The input of the phase-locked loop is connected to the grid voltage signal, and the output provides a phase synchronization clock signal to the disturbance injection module.

8. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The DC voltage control circuit includes: Voltage sampling circuit to collect DC capacitor voltage; The current tracking controller drives the full-bridge circuit to feed DC-side energy back to the grid.

9. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The hardware carriers of the stability monitoring loop and the damping control loop are digital signal processors (DSPs). The disturbance injection module outputs pulse signals through the PWM generator of the DSP, the impedance calculation module is executed by the FFT calculator built into the DSP, and the virtual resistance generation module is updated in real time through the floating-point unit of the DSP. R v .

10. The active damper for pre-oscillation stability monitoring of grid-connected power electronic systems according to claim 1, characterized in that, The active damper is electrically connected to the common coupling point of the power grid through an output interface circuit; the output interface circuit is used to filter out the switching frequency harmonics output by the power electronic converter and match the impedance characteristics between the damper and the power grid.

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