Novel photovoltaic grid-connected reactive power compensation decentralized control device

Abstract

The application provides a novel photovoltaic grid-connected reactive power compensation decentralized control device, which is applied to the technical field of smart grid, and through an electrical acquisition module, the device acquires grid-connected node voltage, current and power characteristic quantities in real time to form complete time series data; an oscillation suppression module identifies local oscillation modes based on the time series data, and generates synchronous damping current through mode consensus and damping compensation to realize active suppression of low-frequency or weak-damping oscillation; a compensation module combines the damping current and the reactive power regulation current to perform coordinate transformation, decomposition and superposition, generates a reactive power compensation current reference, and injects the grid-connected node through a power electronic execution module. Through the above technical means, the application can realize parallel fusion of reactive power regulation and oscillation suppression in the photovoltaic grid-connected system, effectively suppress the cascading outage risk caused by oscillation, and thus enhance the stability of the photovoltaic grid-connected system.

Description

Technical Field

[0001] This application relates to the field of smart grid technology, and in particular to a novel distributed control device for reactive power compensation in photovoltaic grid connection. Background Technology

[0002] With the continuous advancement of smart grid construction and the "dual carbon" target, the penetration rate of distributed photovoltaic power generation in the distribution network has increased rapidly, and it has become an important part of the energy structure transformation. In the process of large-scale grid connection of high-proportion distributed photovoltaic power, the power grid needs to rely extensively on various reactive power compensation devices to maintain voltage stability, reduce grid losses and improve power quality.

[0003] In existing photovoltaic grid-connected systems, distributed reactive power compensation is mainly achieved through the local controller of the photovoltaic inverter, and simple coordination is carried out by exchanging voltage deviation and remaining capacity information through limited neighborhood communication.

[0004] However, in the existing distributed reactive power compensation process for grid-connected photovoltaic systems, the control strategy mainly focuses on adjusting the steady-state voltage deviation and eliminating static voltage errors. It does not identify and analyze the dynamic oscillation characteristics that may occur during grid operation. When a high proportion of distributed photovoltaic systems are connected to the distribution network, the grid's operating state becomes more complex. Specific frequency oscillation components may be superimposed on the voltage and current signals. The existing control method only performs feedback adjustment based on instantaneous voltage amplitude changes and does not extract oscillation-related information. It is difficult to perform directional control of the oscillation components to achieve a suppression effect. Therefore, when the grid experiences low-frequency or weakly damped oscillations, this distributed reactive power compensation method often can only passively respond to voltage fluctuations and cannot effectively provide active damping support for the oscillation components, leading to a greater risk of cascading grid disconnection triggered by the continuous amplification of oscillations. Summary of the Invention

[0005] This application provides a novel distributed control device for reactive power compensation in photovoltaic grid-connected systems. Its core features include: synchronously sampling electrical signals such as voltage and current at grid-connected nodes to form time-series data; extracting local oscillation mode parameters using an oscillation identification unit; exchanging mode information with adjacent nodes through a mode consensus unit to form a dominant oscillation mode; and generating a suppression trigger signal based on this mode. Subsequently, a damping compensation unit calculates a damping compensation current based on the suppression trigger signal, which is then superimposed with the reactive power regulation current calculated by the compensation module to form a reactive power compensation current reference. A power electronic execution module drives the grid-connected power regulation equipment to output the corresponding compensation current, thereby achieving active identification and targeted suppression of oscillation components and reducing the risk of chain-redirection caused by continuous oscillation amplification.

[0006] To achieve the above objectives, this application adopts the following technical solution: This application provides a novel photovoltaic grid-connected reactive power compensation decentralized control device, the device comprising: an electrical acquisition module, an oscillation suppression module, a compensation module, and a power electronic execution module; The electrical acquisition module is electrically connected to the oscillation suppression module and is used to sample the electrical signals of the grid-connected node to generate corresponding time series data. The oscillation suppression module includes an oscillation identification unit, a modal consensus unit, and a damping compensation unit; The oscillation identification unit is used to extract features of the oscillation mode of the grid-connected node based on the time series data to obtain local oscillation mode parameters; The modal consensus unit is communicatively connected to adjacent grid-connected nodes and is used to exchange the local oscillation mode parameters with the oscillation mode parameters of the adjacent grid-connected nodes to form dominant oscillation mode information, and output a corresponding suppression trigger signal according to the dominant oscillation mode information; The damping compensation unit is communicatively connected to the compensation module and is used to determine the corresponding oscillation suppression mode according to the suppression trigger signal. Under the oscillation suppression mode, the corresponding damping compensation current is calculated according to the dominant oscillation mode information to form a damping current component. The compensation module is used to calculate the corresponding reactive power regulation current based on the time series data, form a reactive current component, and superimpose the reactive current component with the damping current component to form a reactive power compensation current reference. The power electronic execution module is used to control the grid-connected power regulation device to output compensation current to the grid-connected node according to the reactive power compensation current reference.

[0007] In some possible implementations, the oscillation identification unit is specifically used for: The time series data is preprocessed to obtain the target analysis sequence; Modal decomposition is performed on the target analysis sequence to extract the corresponding local oscillation frequency, local oscillation damping ratio, and local oscillation amplitude parameters. The corresponding modal energy index is calculated based on the local oscillation frequency, the local oscillation damping ratio, and the local oscillation amplitude parameter. The local oscillation frequency, the local oscillation damping ratio, the local oscillation amplitude parameter, and the modal energy index are associated and encapsulated to form local oscillation mode parameters.

[0008] In some possible implementations, the suppression trigger signal includes a non-oscillation flag signal and an oscillation suppression activation signal, and the modal consensus unit is specifically used for: The system receives oscillation mode parameters sent by adjacent grid-connected nodes, performs frequency matching between the local oscillation mode parameters and the oscillation mode parameters of the adjacent grid-connected nodes, and obtains candidate oscillation mode parameters. The candidate oscillation mode parameters are weighted and fused according to the corresponding mode energy index to obtain the consensus oscillation mode parameters; Calculate the corresponding dominant oscillation energy value based on the consensus oscillation mode parameters; The consensus oscillation mode parameters are associated and encapsulated with the dominant oscillation energy value to form dominant oscillation mode information; If the dominant oscillation energy value in the dominant oscillation mode information is less than a preset trigger threshold, an oscillation-free indicator signal is output. If the dominant oscillation energy value in the dominant oscillation mode information is greater than the preset trigger threshold, an oscillation suppression activation signal is output.

[0009] In some possible implementations, the consensus oscillation mode parameters include consensus oscillation frequency, consensus oscillation damping ratio, and consensus oscillation amplitude parameters, and the damping compensation unit is specifically used for: Upon receiving the oscillation suppression activation signal, the first oscillation suppression mode is selected; In the first oscillation suppression mode, a synchronous oscillation reference signal is generated based on the consensus oscillation frequency in the consensus oscillation mode parameters; The damping gain coefficient is calculated based on the consensus oscillation amplitude and consensus oscillation damping ratio in the consensus oscillation mode parameters. The damping gain coefficient and the synchronous oscillation reference signal are phase-compensated to generate the corresponding damping current component. Upon receiving a no-oscillation flag signal, select the second oscillation suppression mode and set the damping current component to zero.

[0010] In some possible implementations, the compensation module is specifically used for: Receive the damping current component generated by the damping compensation unit; The corresponding reactive power regulation current is calculated based on the time series data to form a reactive current component. The reactive current component and the damping current component are respectively transformed to the synchronous rotating coordinate system through coordinate transformation to obtain the first and second rotating axis components corresponding to the reactive current component, and the third and fourth rotating axis components corresponding to the damping current component. In the synchronous rotating coordinate system, the first rotating axis component of the reactive current component and the third rotating axis component of the damping current component are superimposed to obtain the first rotating axis reference component of the reactive compensation current. The second rotating axis component of the reactive current component is superimposed with the fourth rotating axis component of the damping current component to obtain the second rotating axis reference component of the reactive compensation current. The reactive power compensation current reference is obtained by inverse coordinate transformation of the first and second rotating axis reference components of the reactive power compensation current.

[0011] In some possible implementations, the compensation module is further used for: The amplitude of the reactive power compensation current is calculated based on the first rotating axis reference component and the second rotating axis reference component. If the amplitude of the reactive power compensation current is greater than the rated current capacity of the grid-connected power regulation equipment, a limiting factor is calculated, wherein the limiting factor is the ratio of the rated current capacity to the amplitude of the reactive power compensation current. Multiply the first rotation axis reference component and the second rotation axis reference component by the limiting coefficient respectively to obtain the first rotation axis reference component and the second rotation axis reference component after limiting. The first and second rotating axis reference components after amplitude limiting are subjected to inverse coordinate transformation to obtain the reactive power compensation current reference after amplitude limiting.

[0012] In some possible implementations, the power electronic execution module is specifically used for: Receive the reactive power compensation current reference output by the compensation module; The reactive power compensation current reference is converted into a corresponding control signal, and the grid-connected power regulation device is driven to output the corresponding compensation current to the grid-connected node according to the control signal.

[0013] In some possible implementations, the electrical acquisition module is specifically used for: The voltage and current signals of the grid-connected nodes are synchronously sampled to obtain voltage and current sequences; The amplitude, phase, and frequency information of the grid voltage are extracted from the voltage sequence to form voltage characteristic quantities; The active power, reactive power, and power factor are calculated based on the voltage sequence and the current sequence to form power characteristic quantities; The voltage sequence, the current sequence, the voltage characteristic, and the power characteristic are encapsulated to form time series data.

[0014] In some possible implementations, a protection module is also included; The protection module is electrically connected to both the electrical acquisition module and the power electronic execution module. The protection module is specifically used to: detect the operating status of the grid-connected node based on the time series data; When an abnormal operating state is detected, a protection trigger signal is generated and transmitted to the power electronic execution module.

[0015] In some possible implementations, the power electronic execution module is also used for: Upon receiving the protection trigger signal, the reactive power compensation current reference is shielded, and the grid-connected power regulation equipment is controlled to perform protection actions according to the protection strategy corresponding to the protection trigger signal.

[0016] As can be seen from the above technical solution, this application has the following beneficial effects: 1. This application constructs a multi-node oscillation mode identification and weighted consensus mechanism by jointly using an oscillation identification unit and a modal consensus unit. This mechanism enables unified feature extraction of key oscillation frequencies, amplitudes, and damping ratios, as well as calculation of dominant oscillation energy. This allows for accurate determination of oscillation intensity and proactive triggering of suppression control, thus solving the problem that traditional single-node detection is unable to capture systemic oscillations.

[0017] 2. This application constructs a damping current with the same frequency as the dominant oscillation mode and with energy dissipation characteristics through a damping compensation unit, and injects it into the grid-connected node by merging it with the reactive power compensation current to achieve dynamic matching of compensation amplitude and phase. This allows for intervention in the early stage of oscillation, effectively suppressing the amplification of low-frequency oscillations and improving the dynamic stability and safe operation capability of the distributed photovoltaic grid-connected system.

[0018] 3. This application decomposes and superimposes the reactive current component and the damping current component in a synchronous rotating coordinate system through a compensation module, thereby realizing the parallel integration of reactive power regulation and oscillation suppression functions. This actively suppresses low-frequency oscillations and reduces the risk of cascading shutdown without interfering with conventional reactive power regulation. Attached Figure Description

[0019] The present application will be further described below with reference to the accompanying drawings.

[0020] Figure 1 Example diagram of the first novel photovoltaic grid-connected reactive power compensation distributed control device provided in this application; Figure 2 Example diagram of the second novel photovoltaic grid-connected reactive power compensation distributed control device provided in this application; Figure 3 An example diagram of the third novel photovoltaic grid-connected reactive power compensation distributed control device provided in this application. Detailed Implementation

[0021] The terms "first," "second," and "third," etc., used in this application specification, claims, and drawings are used to distinguish different objects, not to limit a specific order.

[0022] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0023] To ensure clarity and conciseness in the description of the following embodiments, a brief introduction to the related technologies is given first: In existing grid-connected photovoltaic systems, distributed reactive power compensation devices are mainly implemented through the local controller of the photovoltaic inverter itself. During operation, the inverter measures the voltage and current signals of the grid-connected nodes to obtain instantaneous voltage amplitude, phase, and active and reactive power information, and makes reactive power regulation decisions based on this information. Typically, the control strategy adopts voltage closed-loop or power factor control: In voltage closed-loop mode, the inverter calculates the deviation between the grid-connected node voltage and the set reference value, generates a reactive current command, and causes the reactive component of the output current to adjust the node voltage, thereby achieving steady-state voltage control; In power factor control mode, the inverter adjusts the reactive component of the output current according to the measured phase difference between the current and voltage, so that the grid power factor is maintained within the target range, thereby reducing the impact of reactive power fluctuations on the grid.

[0024] To improve coordination, some photovoltaic grid-connected systems also introduce a neighborhood communication mechanism, in which inverters exchange voltage deviation, remaining capacity or load information through a communication network with limited bandwidth to perform simple local coordination. For example, when the voltage of a certain node deviates from the set value, the inverter can refer to the voltage information of the neighboring nodes and adjust its own reactive power output appropriately, thereby avoiding excessive local voltage deviation or the formation of excessive voltage gradient.

[0025] In the control loop, the inverter uses a proportional, integral (PI) or lag compensation controller to calculate the reactive current output command based on the measured voltage deviation. The output reactive current is realized through the power electronic module inside the inverter, specifically including the pulse width modulation control of the power switching devices and the dynamic response of the filter, so as to generate an AC current that conforms to the command and inject it into the grid.

[0026] Research has revealed that existing distributed reactive power compensation devices primarily rely on steady-state voltage deviation for control. This involves measuring the instantaneous voltage amplitude and comparing it to a set reference value to generate reactive current output commands. While this approach can maintain voltage within the target range under static or slowly changing load conditions, it is essentially instantaneous deviation feedback control and fails to analyze the dynamic characteristics of the power grid during operation. Therefore, when rapid disturbances occur at grid-connected nodes or low-frequency or weakly damped oscillations superimposed on voltage and current signals, the controller responds solely based on instantaneous amplitude changes, unable to distinguish between oscillating components and normal fluctuations. This results in reactive power output failing to provide directional damping support for the oscillating components. Furthermore, the device's neighborhood communication coordination is limited to exchanging voltage deviation, remaining capacity, or load information. This information essentially reflects the static or average grid state, not oscillating characteristics. Even with multiple inverters... Local reactive power regulation through communication coordination is merely a simple superposition adjustment based on steady-state deviations, without coordinated analysis and optimization of oscillation frequency, amplitude, or damping ratio. Especially in cases of high photovoltaic integration and inter-node coupling, local regulation may fail to respond promptly or suppress misalignment, potentially leading to the superposition or amplification of oscillations across different nodes. Furthermore, the PI or hysteresis compensation controller used in this device is essentially a linear controller with fixed design parameters, primarily targeting steady-state errors and small disturbances. It lacks adaptive adjustment capabilities for unbalanced disturbances and oscillations at specific frequencies. When the oscillation amplitude increases or the frequency changes, the PI controller cannot dynamically adjust the gain or phase compensation, potentially resulting in phase misalignment between the output current and the oscillation signal. This limits the suppression effect of reactive power compensation on oscillations and may even lead to partial oscillation resonance.

[0027] In summary, existing distributed reactive power compensation devices cannot effectively suppress low-frequency or weakly damped oscillations, which may lead to continuous amplification of the oscillations. Therefore, when the oscillations continue to amplify, the voltage or current of the grid-connected nodes may exceed the safe range of the inverters and protection devices. Once some photovoltaic inverters are disconnected due to overvoltage, undervoltage, or overcurrent, the redistribution of the grid load will exacerbate the voltage fluctuations of other nodes, thereby triggering more equipment to disconnect from the grid, forming a chain reaction and causing a chain disconnection of the photovoltaic grid-connected system.

[0028] Example 1: To solve the above problems, this application provides a novel distributed control device for reactive power compensation in photovoltaic grid-connected systems. Please refer to [link to example]. Figure 1 The device includes: an electrical acquisition module, an oscillation suppression module, a compensation module, and a power electronic execution module.

[0029] The electrical acquisition module is mainly used to synchronously sample and extract the voltage and current signals of the grid-connected nodes, generate time series data, and provide data input for the oscillation suppression module and the compensation module.

[0030] To make the description of the following embodiments clear and concise, a brief introduction to the relevant terms is given first: A grid-connected node is the electrical connection point where a photovoltaic inverter or grid-connected power regulation device connects to the power grid. Changes in the voltage, current, and power at this connection point directly reflect the local dynamic state of the power grid.

[0031] Voltage sequence refers to the sequence data obtained by continuously sampling the instantaneous voltage signal of the grid-connected node through the electrical acquisition module, which records the voltage amplitude and phase information of the grid-connected node at each moment within the sampling period.

[0032] The current sequence is a sequence of data obtained by synchronously sampling the instantaneous current signal of the grid-connected node through an electrical acquisition module, recording the current amplitude and phase information of the node at each moment within the sampling period.

[0033] Voltage characteristics are feature information extracted from voltage sequences to describe the electrical state of nodes, including parameters such as voltage amplitude, phase, and instantaneous frequency.

[0034] Power characteristics are characteristic parameters such as active power, reactive power, and power factor at nodes, which are calculated based on voltage and current sequences.

[0035] Time series data refers to a set of data obtained by encapsulating node voltage sequences, current sequences, voltage characteristics, and power characteristics through electrical acquisition modules. It is used to uniformly represent the complete information on the changes in the electrical state of grid-connected nodes over time.

[0036] In some possible implementation methods, the instantaneous voltage and current signals of the grid-connected node are continuously measured by the electrical acquisition module to form voltage and current sequences. In order to ensure the synchronization of voltage and current signals, the electrical acquisition module can adopt a synchronous sampling method with a fixed sampling period, such as using a unified clock trigger or a synchronization signal to ensure that the voltage and current collected in each sampling period are consistent with the corresponding time points.

[0037] The electrical acquisition module further extracts voltage amplitude, phase, and instantaneous frequency information from the voltage sequence based on amplitude detection and phase analysis methods to form voltage characteristic quantities. Among them, the amplitude information is obtained by rectifying and filtering the voltage sequence, the instantaneous phase is obtained by phase detection algorithm (such as zero-crossing detection or phase calculation based on synchronous reference coordinate system), and the instantaneous frequency is calculated by phase difference of adjacent sampling points or spectrum analysis method, so as to reflect the steady-state voltage level, fluctuation amplitude, and dynamic frequency change of the node.

[0038] Meanwhile, the electrical acquisition module calculates active power, reactive power, and power factor based on the voltage and current sequences of the grid-connected nodes, forming power characteristic quantities. Active power is calculated by measuring the instantaneous product of voltage and current and taking the average value. Reactive power is calculated by the phase difference between voltage and current. Power factor is determined by the ratio of active power to apparent power, thereby quantifying the node load status and reactive power demand.

[0039] During data processing and encapsulation, the electrical acquisition module timestamps and encapsulates voltage sequences, current sequences, voltage characteristics, and power characteristics according to a unified data structure, forming complete time-series data. The encapsulation method can employ segmented frames, packaging data from each sampling period into data frames. These frames include the sampling time identifier, the original voltage value, the current value, and the calculated characteristics. The sampling period, node identifier, and data length information are recorded in the data frame header for rapid parsing and processing by downstream modules. The encapsulated time-series data is transmitted in real-time to the oscillation suppression module via an electrical interface or communication bus. The resulting data not only contains the instantaneous electrical information of the nodes but also reflects their dynamic characteristics and potential oscillation modes, serving as the core data foundation for subsequent oscillation mode identification, modal consensus calculation, and damping compensation current generation.

[0040] In the above implementation, the working principle of the electrical acquisition module is mainly based on real-time sampling, feature extraction, and data encapsulation processing of the electrical signals of the grid-connected nodes. Its core includes four steps: sampling synchronization, signal preprocessing, feature calculation, and time series data output. In the sampling synchronization stage, the electrical acquisition module samples the instantaneous voltage and current signals of the nodes through a unified clock trigger or synchronization signal. The sampling frequency of each sampling cycle can be set in the range of 1~10kHz to fully capture low-frequency oscillations (about 0.1~10Hz) and instantaneous voltage and current fluctuations in the power grid, ensuring that the voltage sequence and current sequence are strictly corresponding in time. This synchronous sampling can effectively capture the instantaneous disturbances and potential oscillation characteristics in the operation of the power grid, ensuring the accuracy of subsequent analysis.

[0041] In the signal preprocessing stage, the electrical acquisition module filters, denoises, and normalizes the acquired raw voltage and current signals to eliminate the influence of high-frequency interference and measurement noise, while maintaining the low-frequency oscillation and dynamic characteristics of the signal without weakening, providing reliable input for oscillation mode identification. Bandpass or low-pass filters can be used for filtering to smooth the amplitude, and digital signal processing technology is used to complete phase calculation to obtain high-precision instantaneous phase information.

[0042] In the characteristic quantity calculation stage, the electrical acquisition module forms voltage characteristic quantities by performing amplitude detection, phase analysis, and instantaneous frequency calculation on the preprocessed voltage sequence. The amplitude is obtained through rectification and filtering, the phase is obtained through zero-crossing detection or phase calculation method based on synchronous rotating coordinate system, and the instantaneous frequency is calculated by phase difference of adjacent sampling points or Fourier transform or spectrum analysis method. At the same time, active power, reactive power, and power factor are calculated using voltage and current sequences to form power characteristic quantities to quantify node load status and reactive power demand. The above characteristic quantities not only reflect the steady-state state of the node, but also reflect dynamic fluctuations and potential oscillation characteristics, providing basic data support for the compensation module and oscillation suppression module.

[0043] In the time-series data encapsulation stage, the electrical acquisition module encapsulates voltage sequences, current sequences, voltage characteristics, and power characteristics according to a unified data structure and timestamps to form complete time-series data. Encapsulation employs a segmented frame approach, packaging data from each sampling period into data frames, including the sampling time, original voltage value, current value, and calculated characteristics. The sampling period, node identifier, and data length information are recorded in the data frame header for rapid parsing and processing by downstream modules. The encapsulated time-series data is output in real-time to the oscillation suppression module via an electrical interface, ensuring that subsequent oscillation mode identification, mode consensus calculation, and damping compensation current generation are based on accurate and complete dynamic electrical information, enabling real-time response and control of the power grid's dynamic characteristics and potential oscillation modes.

[0044] By implementing the electrical acquisition module, this application can realize the dynamic detection of grid-connected nodes, and convert the instantaneous electrical signals and power characteristics of the grid-connected nodes into data that can be used for oscillation identification and reactive power compensation calculation. This provides reliable data support for the active suppression of low-frequency oscillations or weakly damped oscillations, thereby improving the stability and security of distributed photovoltaic grid-connected systems.

[0045] Example 2: The oscillation suppression module includes an oscillation identification unit. Please refer to [link / reference]. Figure 2 .

[0046] The oscillation identification unit is mainly used to extract features of the oscillation modes of grid-connected nodes based on time series data, and obtain local oscillation mode parameters.

[0047] The aforementioned local oscillation mode parameters refer to a set of parameters that quantitatively describe the oscillation characteristics obtained by the oscillation identification unit after extracting features of the oscillation modes of the grid-connected node based on time series data.

[0048] To make the description of the following embodiments clear and concise, a brief introduction to the relevant terms is given first: Local oscillation frequency: describes the dominant frequency of the oscillation component of the grid-connected node, reflecting the periodic characteristics of the oscillation signal.

[0049] Local oscillation damping ratio: Represents the rate at which oscillation energy decays, used to assess the degree of oscillation decay or the degree of weak damping.

[0050] Local oscillation amplitude: reflects the strength of the oscillation signal and quantifies the actual impact of the oscillation on the voltage or current of the grid-connected node.

[0051] Modal energy index: A quantitative value calculated by combining oscillation frequency, amplitude and damping information, used to measure the contribution of the oscillation mode to the overall oscillation of the photovoltaic grid-connected system.

[0052] In some possible implementations, the oscillation identification unit receives time-series data of the grid-connected nodes sent by the electrical acquisition module, including voltage sequences, current sequences, voltage characteristics, and power characteristics. To address potential high-frequency noise, measurement errors, and discontinuous data in the original signal, the oscillation identification unit preprocesses the signal using digital filters (such as bandpass or low-pass filters), and simultaneously performs interpolation, normalization, and detrending processing on the time-series data to generate a target analysis sequence suitable for modal analysis.

[0053] In the mode decomposition stage, the oscillation identification unit can employ various calculation methods to extract the oscillation characteristics of the target analysis sequence. The oscillation identification unit decomposes the target analysis sequence into several independent mode components, each representing the oscillation component of the photovoltaic grid-connected system within a specific frequency range. To achieve this decomposition, an empirical mode decomposition method can be used. This involves iteratively filtering local maxima and minima in the signal to construct the signal's envelope curve, and obtaining a single oscillation component based on envelope averaging. This process is repeated until all mode components are extracted, thus decomposing the original signal into several oscillation components from low to high frequencies. Another method is to use the Hilbert-Huang transform, performing a Hilbert transform on each mode component to obtain the instantaneous amplitude and phase, and then calculating the instantaneous frequency to achieve accurate separation of different frequency components. Alternatively, an improved frequency domain analysis method can be used, identifying the main oscillation frequencies and their amplitude distributions by performing Fourier transform or power spectrum analysis on the sequence.

[0054] During the parameter extraction phase, for each modal component, the oscillation identification unit obtains its local oscillation frequency, local oscillation damping ratio, and local oscillation amplitude parameters using a specific calculation method. The oscillation frequency can be obtained by identifying the main peak position of the modal component in the spectrum, or by calculating the reciprocal of the period from the interval between signal zero-crossing points. The damping ratio is calculated by exponentially fitting the modal component envelope or using the logarithmic decay method, i.e., analyzing the rate at which the modal signal amplitude decays over time. The oscillation amplitude is obtained by calculating the maximum amplitude, root mean square value, or standard deviation of the modal component.

[0055] The oscillation identification unit comprehensively calculates the local oscillation frequency, local oscillation damping ratio, and local oscillation amplitude parameters. Specifically, the local oscillation amplitude parameter is squared to reflect the energy magnitude, and then weighted according to the local oscillation frequency to make low-frequency or key frequency modes contribute more to the energy index. At the same time, the energy is adjusted in conjunction with the local damping ratio, with weakly damped modes having higher weights to reflect their potential risks in the overall oscillation. After calculating the modal energy index, the oscillation identification unit associates and encapsulates the local oscillation frequency, local oscillation damping ratio, local oscillation amplitude parameters, and modal energy index to form complete local oscillation modal parameters.

[0056] Example 3: The oscillation suppression module includes a modal consensus unit. Please refer to [link / reference]. Figure 2 .

[0057] The modal consensus unit communicates with adjacent grid-connected nodes and is mainly used to exchange local oscillation mode parameters with the oscillation mode parameters of adjacent grid-connected nodes to form dominant oscillation mode information, and output corresponding suppression trigger signals according to the dominant oscillation mode information.

[0058] To make the description of the following embodiments clear and concise, a brief introduction to the relevant terms is given first: Candidate oscillation mode parameters: After frequency matching, the set of parameters that may belong to the same oscillation mode are selected from the local oscillation mode parameters and the oscillation mode parameters of adjacent nodes.

[0059] Consensus Oscillation Mode Parameters: Oscillation characteristic parameters obtained by weighting and fusing candidate oscillation mode parameters according to mode energy index, representing the consensus characteristics of multiple grid-connected nodes for the same oscillation mode.

[0060] Dominant Oscillation Energy Value: An indicator used to quantify the strength of the oscillation mode in the current photovoltaic grid-connected system. It is usually calculated by weighting the oscillation amplitude, frequency and damping characteristics, and is used to determine whether the oscillation has reached the threshold for triggering suppression.

[0061] Suppression trigger signal: A control signal output by the modal consensus unit to indicate the oscillation state, including a no-oscillation flag signal and an oscillation suppression activation signal.

[0062] Adjacent grid-connected nodes refer to photovoltaic grid-connected nodes that have a direct electrical connection with this grid-connected node in terms of grid topology or control logic, or that can exchange information in real time.

[0063] Adjacent grid-connected nodes can include the following two categories: Grid-connected nodes that are electrically close and have directly connected current paths within the same busbar, distribution branch, or transformer connection range. For example, photovoltaic inverters connected to the same low-voltage busbar, or grid-connected nodes directly connected through the same medium-voltage distribution line.

[0064] In distributed control or communication networks, a grid-connected node is one that can directly exchange oscillation mode parameters with the local node. Such nodes do not necessarily depend on physical electrical distance; for example, nodes that achieve real-time data sharing via local area networks, fiber optic ring networks, or wireless communication links.

[0065] In some possible implementations, the modal consensus unit receives oscillation mode parameters sent by neighboring network nodes and simultaneously acquires its own local oscillation mode parameters. The modal consensus unit compares its local oscillation mode with the modes of neighboring nodes using a frequency matching algorithm, selecting corresponding oscillation modes as candidate oscillation mode parameters. During the matching process, a preset frequency deviation threshold or modal similarity index can be used to determine whether two modes belong to the same oscillation pattern.

[0066] After the candidate oscillation mode parameters are screened, the modal consensus unit performs weighted fusion based on the modal energy index corresponding to each candidate mode parameter. The weighting method can take into account the magnitude of the modal energy value, so that modes with low damping, critical frequencies, or higher energy have a greater proportion in the fusion result. The fused result is the consensus oscillation mode parameter, which can represent the unified characteristic perception of the oscillation mode by multiple grid-connected nodes in the photovoltaic grid-connected system.

[0067] Furthermore, the modal consensus unit calculates the dominant oscillation energy value based on the consensus oscillation mode parameters. If the dominant oscillation energy value is less than a preset trigger threshold, the modal consensus unit outputs a no-oscillation indicator signal, indicating that the photovoltaic grid-connected system is in a stable state; if the dominant oscillation energy value is greater than the preset trigger threshold, the modal consensus unit outputs an oscillation suppression activation signal, which is used to trigger the damping compensation unit to perform oscillation suppression operation.

[0068] For example, to effectively identify the same oscillation mode, the modal consensus unit uses a frequency matching method to screen oscillation mode parameters. The unit compares the oscillation frequency of the local oscillation mode parameter with the oscillation mode frequencies of adjacent grid-connected nodes pairwise. A preset frequency deviation threshold is used to determine whether they belong to the same oscillation mode. For instance, if the frequency difference is less than a set positive or negative percentage range, the two modes can be considered to belong to the same oscillation mode. Simultaneously, to improve matching accuracy, modal similarity indicators can be introduced, including damping ratio difference and amplitude ratio. These indicators are considered comprehensively to form a matching score, thereby screening out oscillation modes with similar frequencies and characteristics as candidate oscillation mode parameters.

[0069] After the candidate oscillation mode parameters are determined, the modal consensus unit uses a weighted fusion method to generate consensus oscillation mode parameters. The weighted fusion method may include the following steps: normalizing the modal energy index corresponding to each candidate oscillation mode parameter to make the energy dimensions of different grid-connected nodes consistent; assigning weights to each mode according to oscillation characteristics, for example, weakly damped modes with small damping ratios, modes with frequencies in the critical stability range, and modes with large modal energy have higher weights; and fusing the frequency, damping ratio, and amplitude parameters of multiple candidate oscillation mode parameters by weighted averaging to obtain unified consensus oscillation mode parameters.

[0070] Based on the consensus oscillation mode parameters, the mode consensus unit further calculates the dominant oscillation energy value. Since the low-frequency oscillations of a photovoltaic grid-connected system are essentially a periodic exchange process between voltage, current, and power, their intensity is jointly determined by the magnitude of the disturbance energy represented by the oscillation amplitude and the energy dissipation capacity represented by the oscillation damping ratio. The larger the oscillation amplitude, the higher the energy stored and exchanged by the system per unit time; the smaller the oscillation damping ratio, the weaker the system's ability to attenuate oscillation energy, and the longer the oscillation duration. Therefore, the dominant oscillation energy value must simultaneously reflect a positive correlation with the oscillation amplitude and a negative correlation with the oscillation damping ratio.

[0071] The specific calculation method is as follows: the consensus oscillation amplitude parameter in the consensus oscillation mode parameters is squared to characterize the equivalent energy storage intensity of the oscillation mode. The square of the consensus oscillation amplitude parameter is approximately proportional to the instantaneous oscillation energy, thus reflecting the direct impact of oscillation on the dynamic stability of the power grid. The consensus oscillation damping ratio is introduced as an energy dissipation capacity indicator. The dominant oscillation energy value is obtained by calculating the ratio of the square of the consensus oscillation amplitude parameter to the consensus oscillation damping ratio. This ratio represents the equivalent residual oscillation energy per unit damping dissipation capacity.

[0072] Under this calculation method, as the oscillation amplitude increases, the dominant oscillation energy value also increases; when the oscillation damping ratio decreases, the dominant oscillation energy value also increases significantly. Especially when the oscillation damping ratio approaches zero, the dominant oscillation energy value will exhibit a non-linear upward trend, thus accurately reflecting the physical characteristic of a sharp increase in oscillation risk under weak damping conditions. The dominant oscillation energy value obtained through the above calculation method has clear physical meaning and monotonicity, and can be used as the basis for judging the output of the no-oscillation indicator signal or the oscillation suppression activation signal of the modal consensus unit, thereby providing a quantitative triggering condition for the damping compensation unit and realizing accurate identification and active suppression of low-frequency oscillations of grid-connected nodes.

[0073] Through the above-mentioned frequency matching, weighted fusion and dominant oscillation energy calculation methods, this application can realize multi-node collaborative oscillation identification and suppression, and improve the oscillation detection and active control capabilities of distributed photovoltaic grid-connected systems.

[0074] Example 4: The oscillation suppression module includes a damping compensation unit. Please refer to [link / reference]. Figure 3 .

[0075] The damping compensation unit is communicatively connected to the compensation module and is mainly used to determine the corresponding oscillation suppression mode based on the suppression trigger signal. In the oscillation suppression mode, the corresponding damping compensation current is calculated based on the dominant oscillation mode information to form the damping current component.

[0076] To make the description of the following embodiments clear and concise, a brief introduction to the relevant terms is given first: First oscillation suppression mode: an active damping enhancement mode activated when the dominant oscillation energy value exceeds a preset trigger threshold.

[0077] Second oscillation suppression mode: The normal operation mode maintained when the dominant oscillation energy value is less than the preset trigger threshold. In this mode, no damping compensation current is output.

[0078] Synchronous oscillation reference signal: A sinusoidal reference signal synchronized with the consensus oscillation frequency, used to construct a compensation signal that is in sync with the oscillation mode.

[0079] Damping gain coefficient: A proportionality coefficient calculated based on the consensus oscillation amplitude and the consensus oscillation damping ratio, used to adjust the magnitude of the damping current component.

[0080] Damped current component: The current component used to offset or attenuate the dominant oscillation mode is injected into the grid-connected node through the power electronic actuation module.

[0081] In some possible implementations, when the modal consensus unit outputs an oscillation suppression activation signal, the damping compensation unit enters the first oscillation suppression mode. A synchronous oscillation reference signal is generated based on the consensus oscillation frequency, which is frequency-consistent with the current dominant oscillation mode, to ensure that the compensation current accurately applies to the target oscillation frequency. The damping gain coefficient is calculated based on the consensus oscillation amplitude parameter and the consensus oscillation damping ratio. The damping gain coefficient is constructed according to the principle of positive correlation with oscillation amplitude and negative correlation with damping ratio, so that the larger the oscillation amplitude or the smaller the damping ratio, the higher the damping gain coefficient, thereby enhancing the compensation strength.

[0082] After obtaining the damping gain coefficient, the damping compensation unit applies the damping gain coefficient to the synchronous oscillation reference signal and performs phase compensation processing. The purpose of phase compensation is to make the generated damping current component form a phase relationship with the original oscillation signal that is conducive to energy dissipation. For example, in power oscillation, it forms a current response opposite to the oscillation velocity direction, thereby achieving an energy absorption effect. The signal after phase compensation is the damping current component. This current component is superimposed with the reactive power regulation current and injected into the grid-connected node through the power electronic execution module to achieve active suppression of the dominant oscillation mode.

[0083] For example, the damping compensation unit uses phase-locked tracking to generate a synchronous oscillation reference signal. The consensus oscillation frequency is used as the angular frequency input, and a continuous phase accumulator is constructed. The oscillation phase is obtained by integrating the angular frequency, and then a standard sine or cosine signal is generated based on this phase as the synchronous oscillation reference signal. To improve frequency tracking stability, phase smoothing filtering or small-amplitude limiting constraints can be introduced during phase generation to avoid transient impacts on the compensation current caused by frequency abrupt changes. The synchronous oscillation reference signal generated in this way maintains frequency consistency with the dominant oscillation mode, providing a synchronous reference for subsequent damping control. The damping compensation unit calculates the damping gain coefficient based on the consensus oscillation amplitude parameter and the consensus oscillation damping ratio. The unit characterizes the oscillation intensity by proportionally amplifying the consensus oscillation amplitude, while simultaneously introducing the consensus oscillation damping ratio into the denominator as a dissipation capacity adjustment factor, ensuring that a smaller damping ratio results in a larger gain. To avoid excessive gain amplification due to an excessively small damping ratio, a minimum damping limit or upper limit constraint can be set during the calculation process, and the overall compensation intensity can be calibrated using a preset proportional coefficient, thereby achieving a uniform adjustment scale across grid-connected devices of different capacities. The damping gain coefficient obtained through the above calculation can dynamically reflect the degree of oscillation risk, ensuring that the compensation current amplitude matches the oscillation intensity. After obtaining the damping gain coefficient, the damping compensation unit modulates the synchronous oscillation reference signal and performs phase compensation processing. The purpose of phase compensation processing is to create a phase difference between the damping compensation current and the original oscillation signal that is conducive to energy dissipation, thereby increasing the equivalent damping of the photovoltaic grid-connected system. Specifically, the damping compensation unit can perform a proportional calculation between the damping gain coefficient and the reference signal to match the amplitude of the output signal with the current oscillation intensity, thus obtaining a candidate signal for the amplitude-modulated oscillation current. After amplitude modulation, the damping compensation unit performs phase compensation processing on this candidate signal. The core objective of phase compensation is to ensure that the phase of the damping current component is in a phase relationship with the original oscillation signal that is conducive to energy dissipation, even if the injected current changes in the opposite direction to the oscillation energy, thereby achieving enhanced equivalent damping. To this end, the target phase offset angle can be determined based on the consensus oscillation damping ratio or the oscillation phase change rate. When the damping is small, a larger phase offset angle is set to enhance the dissipation effect; when the damping is large, a smaller phase offset angle is set to avoid overcompensation.

[0084] Phase compensation processing can be achieved in the following ways: First, a fixed-angle phase rotation is performed on the synchronous oscillation reference signal, that is, a preset phase compensation amount is superimposed during the phase generation process, so that the output signal leads or lags behind the original oscillation signal by a certain angle; Second, a phase component orthogonal to the synchronous oscillation reference signal is constructed, and the synthesis of arbitrary phase offset angle is achieved by proportionally superimposing the reference signal and the orthogonal component; Third, a component opposite to the direction of oscillation velocity is constructed based on the trend of oscillation signal change, so that the damping compensation current cancels out the direction of oscillation power change, thereby achieving energy absorption.

[0085] The signal after phase compensation processing is the damped current component. This damped current component matches the dominant oscillation mode in frequency, matches the oscillation intensity in amplitude, and has energy dissipation characteristics in phase. When this damped current component is injected into the grid-connected node through the power electronic actuator module, it can change the phase relationship between the node voltage and current, increase the system's equivalent damping coefficient, reduce the oscillation amplitude, and achieve active suppression of the dominant oscillation mode.

[0086] In some possible implementations, when the modal consensus unit outputs a no-oscillation flag signal, the damping compensation unit enters the second oscillation suppression mode, sets the damping current component to zero, and restores the device to the normal reactive power regulation operation state, avoiding the introduction of unnecessary control disturbances when the photovoltaic grid-connected system is stable.

[0087] This application identifies oscillation modes in a photovoltaic grid-connected system through a modal consensus unit, and constructs a compensation current with the same frequency as the mode and energy dissipation characteristics by a damping compensation unit. This achieves an active increase in the equivalent damping of the system. The compensation intensity and phase can be adjusted according to the identified oscillation frequency, amplitude and damping characteristics, thereby intervening in the early stage of oscillation amplification, preventing the risk of voltage over-limit or cascading grid disconnection caused by the continuous growth of oscillation, and improving the dynamic stability and safe operation capability of the distributed photovoltaic grid-connected system.

[0088] Example 5: The compensation module is mainly used to calculate the corresponding reactive power regulation current based on time series data, forming a reactive current component. This reactive current component is then superimposed with the damping current component to form a reactive power compensation current reference. Please refer to [link / reference]. Figure 1 .

[0089] To make the description of the following embodiments clear and concise, a brief introduction to the relevant terms is given first: Reactive current component: The regulating current component used to maintain the stability of grid-connected node voltage, calculated based on time series data, and mainly used for reactive power regulation.

[0090] Damped current component: The current component generated by the damping compensation unit to suppress the dominant oscillation mode, which has specific frequency and phase characteristics.

[0091] Synchronous rotating coordinate system: A rotating coordinate system established with the fundamental voltage angular frequency of the power grid as the rotating reference. It is used to decompose the current in the three-phase stationary coordinate system into two mutually orthogonal rotating axis components to achieve decoupling control.

[0092] First and second rotating axis components: Two orthogonal axial components obtained by decomposing the reactive current component in a synchronous rotating coordinate system.

[0093] The third and fourth rotational axis components are two orthogonal axial components obtained by decomposing the damping current component in a synchronous rotating coordinate system.

[0094] Reactive power compensation current reference: The final current control command after integrating reactive power regulation current and damping compensation current.

[0095] In some possible implementations, the compensation module receives the damped current component output by the damping compensation unit and simultaneously calculates the reactive power regulation current based on the time-series data generated by the electrical acquisition module, forming the reactive current component. The time-series data includes the voltage sequence, current sequence, and power characteristics of the grid-connected nodes, and the reactive power regulation demand is determined through voltage deviation calculation or reactive power control algorithms.

[0096] Because the three-phase currents are correlated in the natural coordinate system, it is not conducive to independently adjusting the reactive current component and the oscillation suppression component. Therefore, the reactive current component and the damping current component are transformed to the synchronous rotating coordinate system through coordinate transformation by the compensation module. Through this transformation, the reactive current component and the damping current component are decomposed into two mutually orthogonal rotating axis components.

[0097] In a synchronous rotating coordinate system, the first rotating axis component of the reactive current component and the third rotating axis component of the damping current component are superimposed along the same axis to obtain the first rotating axis reference component of the reactive compensation current; the second rotating axis component of the reactive current component and the fourth rotating axis component of the damping current component are superimposed along the corresponding axis to obtain the second rotating axis reference component of the reactive compensation current. Since the two rotating axes are orthogonal to each other, axial superposition will not introduce intersection, thus realizing the parallel integration of reactive power regulation function and oscillation suppression function.

[0098] After completing the superposition of the rotating axis components, the compensation module transforms the obtained first and second rotating axis reference components back to the three-phase stationary coordinate system through inverse coordinate transformation to form a reactive power compensation current reference. This reactive power compensation current reference simultaneously contains the reactive power component required for voltage support and the damping component required for oscillation suppression, and is output to the grid-connected node by the power electronic execution module.

[0099] For example, a synchronous rotating coordinate system is a dynamic coordinate system constructed with the fundamental voltage angular frequency of the power grid as the rotating reference. In a three-phase power system, the three-phase currents change periodically in a natural stationary coordinate system, and the control quantity oscillates over time, which is not conducive to achieving steady-state control. By establishing a rotating coordinate system with the phase of the power grid voltage as the reference, the periodically changing AC quantity can be converted into an approximately constant DC quantity, thereby simplifying the control structure. Furthermore, the synchronous rotating coordinate system projects the three-phase current onto two orthogonal rotating axes, forming two rotating axis components. One rotating axis component is usually aligned with the power grid voltage vector and is used to characterize the current component related to active or reactive power regulation; the other rotating axis component is orthogonal to the above rotating axis component and is used to characterize another independent component. Since the two rotating axes are mathematically independent, the control of the current component can be achieved in this coordinate system.

[0100] In this application, the orthogonality of the synchronous rotating coordinate system is utilized to integrate the reactive power regulation function and the oscillation suppression function under a unified reference frame, thereby avoiding the phase deviation and interference that may occur when directly superimposed in the natural coordinate system.

[0101] For example, after completing the coordinate transformation, the compensation module obtains the first and second rotating axis components corresponding to the reactive current component, and the third and fourth rotating axis components corresponding to the damping current component.

[0102] Since the reactive current component and the damping current component adopt the same synchronous rotation angle during the transformation process, the third rotation axis component and the first rotation axis component are on the same physical axis, and the fourth rotation axis component and the second rotation axis component are on the same physical axis, and the two are superimposed.

[0103] The first step is to algebraically superimpose the first rotating axis component of the reactive current component with the third rotating axis component of the damping current component to obtain the first rotating axis reference component of the reactive compensation current. This superposition is a linear superposition along the same axis and does not involve phase rotation, thus ensuring the synergistic effect of reactive power regulation and damping enhancement along this axis.

[0104] The second step involves algebraically superimposing the second rotating axis component of the reactive current component with the fourth rotating axis component of the damping current component to obtain the second rotating axis reference component of the reactive compensation current. This process is also a coaxial superposition, ensuring that the two control functions contribute independently along the orthogonal axes.

[0105] During the superposition process, amplitude limiting mechanisms or priority constraint mechanisms can be set according to the operating status of the photovoltaic grid-connected system. For example, when the damping compensation current component is too large and may affect the inverter current capacity, the total current amplitude can be constrained to ensure the safe operation of the device. For instance, after the compensation module completes the superposition of the first rotating axis reference component and the second rotating axis reference component, the compensation module can calculate the amplitude of the reactive power compensation current based on the first rotating axis reference component and the second rotating axis reference component. Since the two rotating axis components in the synchronous rotating coordinate system constitute an orthogonal component relationship, the amplitude of the reactive power compensation current can be obtained by taking the square root of the sum of the squares of the two rotating axis reference components, thereby obtaining the equivalent current amplitude corresponding to the current integrated control output. This amplitude reflects the total current demand level after integrating the reactive power regulation function and the oscillation suppression function.

[0106] The compensation module compares the calculated reactive power compensation current amplitude with the rated current capacity of the grid-connected power regulation equipment. When the reactive power compensation current amplitude is less than or equal to the rated current capacity, it indicates that the current control output has not exceeded the equipment's carrying capacity, and the inverse coordinate transformation output current reference can be directly executed; when the reactive power compensation current amplitude is greater than the rated current capacity, it indicates that the fusion control command has exceeded the equipment's allowable range, and the compensation module enters the amplitude limiting control process.

[0107] During the limiting control process, the compensation module calculates the limiting coefficient, which is the ratio between the rated current capacity and the current reactive power compensation current amplitude. This limiting coefficient is a scaling factor less than one, used to proportionally scale the current reference component in the rotating coordinate system. The compensation module multiplies the first and second rotating axis reference components by the limiting coefficient, respectively, to obtain the limited first and second rotating axis reference components. Since both components are scaled using the same limiting coefficient, the original current vector direction remains unchanged during scaling, and only the amplitude is compressed proportionally, thus avoiding control direction deviation or functional priority imbalance. After completing the limiting process, the compensation module transforms the limited first and second rotating axis reference components to the three-phase stationary coordinate system through inverse coordinate transformation, forming the limited reactive power compensation current reference, which is then output to the power electronic actuator to perform current control.

[0108] After obtaining the first and second rotating axis reference components, the compensation module transforms the current reference value in the rotating coordinate system back to the three-phase stationary coordinate system through a reverse coordinate transformation, forming a reactive power compensation current reference. This current reference includes both the reactive power component required for voltage support and the damping component used for oscillation suppression.

[0109] This application achieves a structural superposition of reactive power regulation and oscillation suppression by performing current component decomposition and axial corresponding superposition in a synchronous rotating coordinate system. The synchronous rotating coordinate system transforms AC quantities into independently controllable orthogonal components, making different control objectives mathematically independent. A fused output is then achieved through linear superposition along the same axis. Compared to directly superimposing current signals in a three-phase stationary coordinate system, this application avoids compensation weakening or control conflict problems caused by phase misalignment, improving control accuracy and dynamic response performance. Simultaneously, it superimposes damping enhancement functions without altering the original reactive power regulation control framework, thereby achieving active stability support for low-frequency grid oscillations in the photovoltaic grid-connected system.

[0110] Example 6: The power electronic execution module is mainly used to control the grid-connected power regulation equipment to output compensation current to the grid-connected node according to the reactive power compensation current reference. Please refer to [link / reference]. Figure 1 and Figure 3 .

[0111] Control signals: Electrical quantities used by power electronic actuators to drive power regulation equipment, such as pulse width modulation signals, voltage commands, or current reference signals.

[0112] Grid-connected power regulation equipment: Equipment capable of rapidly responding to control signals and outputting current, such as grid-connected inverters, static synchronous compensators (STATCOM), static var compensators (SVC), or other power electronic devices.

[0113] In some possible implementations, the power electronic execution module receives a reactive power compensation current reference output from the compensation module. This reference contains current amplitude and phase information for the target grid-connected node. Internally, the module parses and converts the reactive power compensation current reference into an internal representation suitable for power regulation equipment. For example, it converts the current reference in a three-phase stationary coordinate system into a pulse-width modulation amplitude or voltage-current command recognizable by the equipment. The power electronic execution module generates corresponding control signals based on the parsed reactive power compensation current reference. For inverter-type equipment, space vector pulse width modulation or sinusoidal pulse width modulation techniques can be used to convert the current amplitude and phase into corresponding switching control modes, ensuring that the output current closely matches the reference signal in amplitude and phase. For STATCOM or SVC equipment, precise reactive current output is achieved by adjusting the conduction state of the controllable reactor or power electronic bridge arm. Based on the generated control signal, the power electronic execution module drives the grid-connected power regulation equipment to output compensation current at the target grid-connected node. The output compensation current consists of two parts: a reactive power regulation current to maintain node voltage stability and a damping compensation current to actively suppress node oscillations. By rapidly responding to control signals, the power electronic actuator can adjust the output current within a millisecond timescale, thereby ensuring that oscillation suppression and reactive power regulation work synchronously on the power grid.

[0114] This application provides a novel distributed control device for reactive power compensation in grid-connected photovoltaic systems, which also includes a protection module. Please refer to [link / reference]. Figure 3 .

[0115] The protection module is electrically connected to both the electrical acquisition module and the power electronic execution module. The protection module is mainly used to detect the operating status of the grid-connected node based on the time series data. When an abnormal operating status is detected, a protection trigger signal is generated and transmitted to the power electronic execution module.

[0116] Among them, the protection trigger signal refers to the control signal generated by the protection module when the grid-connected node detects an abnormal operating state (such as overcurrent, overvoltage, undervoltage, frequency deviation, or reverse power flow), which is used to notify the power electronic execution module to switch to protection mode or stop outputting compensation current.

[0117] Abnormal operating status: refers to the state of photovoltaic grid-connected nodes deviating from the normal operating range, including but not limited to voltage or current exceeding the rated value, abnormal frequency, reverse power flow, short circuit or open circuit, etc.

[0118] The protection module receives time-series data transmitted from the electrical acquisition module, including voltage sequences, current sequences, and power characteristics. It continuously monitors the operating status of the grid-connected nodes by calculating indicators such as voltage and current amplitudes, frequency deviations, power flow direction, and instantaneous power in real time.

[0119] The protection module compares the detected indicators with preset safety thresholds. If any indicator exceeds the safety threshold or shows a continuous deviation trend, the grid-connected node is determined to be in an abnormal operating state. The thresholds can be set separately for different parameters such as voltage, current, frequency, power, and reverse power.

[0120] After determining the abnormal state, the protection module generates a corresponding protection trigger signal. This signal may contain information such as trigger type, severity, and duration, which is used to guide the power electronic execution module to take corresponding actions.

[0121] The protection trigger signal is sent to the power electronic actuator module via electrical connection, driving it to respond quickly, such as cutting off the compensation current output, switching to protection mode, or reducing power output, thereby preventing equipment damage and maintaining grid safety.

[0122] For example, in addition to receiving the reactive power compensation current reference and controlling the output compensation current of the grid-connected power regulation equipment, the power electronic execution module can also execute protection strategies upon receiving a protection trigger signal from the protection module. When the protection trigger signal is received, the power electronic execution module immediately blocks the current reactive power compensation current reference to prevent further injection of compensation current and additional burden on the equipment or grid. Based on the protection type and strategy contained in the protection trigger signal, the power electronic execution module adjusts the operating state of the grid-connected power regulation equipment, such as quickly cutting off power output, reducing voltage or current levels, switching to protection mode, or enabling overcurrent / overvoltage protection functions, thereby preventing damage to the grid-connected node equipment.

[0123] In this application, the protection module can work in conjunction with the oscillation suppression module, the compensation module, and the power electronic execution module. When the photovoltaic grid-connected node oscillates or becomes abnormal, it can trigger damping compensation to suppress the oscillation and also trigger protection actions to prevent damage to the photovoltaic grid-connected system, thus achieving dual protection of safety and dynamic stability.

[0124] The novel photovoltaic grid-connected reactive power compensation distributed control device provided in this application synchronously samples and encapsulates the voltage, current, and power characteristics of the grid-connected nodes through an electrical acquisition module. The oscillation suppression module accurately identifies low-frequency or weakly damped oscillations based on mode decomposition and multi-node mode consensus algorithms. It generates a damping current with the same frequency and phase optimization as the dominant oscillation mode through a damping compensation unit. Combined with the reactive current calculated by the compensation module, the current is synchronously rotated and superimposed to form a reactive power compensation current reference injection into the grid-connected node. This method combines data-driven and physical energy dissipation principles to adjust the oscillation amplitude and damping characteristics, enabling proactive intervention in the distributed photovoltaic grid-connected system at the initial stage of oscillation. This suppresses oscillation propagation, prevents voltage over-limit or local grid disconnection risks, and thus achieves enhanced dynamic stability and safe operation assurance from node level to multi-node collaboration in actual operating scenarios.

[0125] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the appended claims and their equivalents.

Claims

1. A novel photovoltaic grid-connected reactive power compensation distributed control device, characterized in that, The device includes: an electrical acquisition module, an oscillation suppression module, a compensation module, and a power electronic execution module; The electrical acquisition module is electrically connected to the oscillation suppression module and is used to sample the electrical signals of the grid-connected node to generate corresponding time series data. The oscillation suppression module includes an oscillation identification unit, a modal consensus unit, and a damping compensation unit; The oscillation identification unit is used to extract features of the oscillation mode of the grid-connected node based on the time series data to obtain local oscillation mode parameters; The modal consensus unit is communicatively connected to adjacent grid-connected nodes and is used to exchange the local oscillation mode parameters with the oscillation mode parameters of the adjacent grid-connected nodes to form dominant oscillation mode information, and output a corresponding suppression trigger signal according to the dominant oscillation mode information; The damping compensation unit is communicatively connected to the compensation module and is used to determine the corresponding oscillation suppression mode according to the suppression trigger signal. Under the oscillation suppression mode, the corresponding damping compensation current is calculated according to the dominant oscillation mode information to form a damping current component. The compensation module is used to calculate the corresponding reactive power regulation current based on the time series data, form a reactive current component, and superimpose the reactive current component with the damping current component to form a reactive power compensation current reference. The power electronic execution module is used to control the grid-connected power regulation device to output compensation current to the grid-connected node according to the reactive power compensation current reference.

2. The apparatus according to claim 1, characterized in that, The oscillation identification unit is specifically used for: The time series data is preprocessed to obtain the target analysis sequence; Modal decomposition is performed on the target analysis sequence to extract the corresponding local oscillation frequency, local oscillation damping ratio, and local oscillation amplitude parameters. The corresponding modal energy index is calculated based on the local oscillation frequency, the local oscillation damping ratio, and the local oscillation amplitude parameter. The local oscillation frequency, the local oscillation damping ratio, the local oscillation amplitude parameter, and the modal energy index are associated and encapsulated to form local oscillation mode parameters.

3. The apparatus according to claim 1, characterized in that, The suppression trigger signal includes a no-oscillation flag signal and an oscillation suppression activation signal, and the modal consensus unit is specifically used for: The system receives oscillation mode parameters sent by adjacent grid-connected nodes, performs frequency matching between the local oscillation mode parameters and the oscillation mode parameters of the adjacent grid-connected nodes, and obtains candidate oscillation mode parameters. The candidate oscillation mode parameters are weighted and fused according to the corresponding mode energy index to obtain the consensus oscillation mode parameters; Calculate the corresponding dominant oscillation energy value based on the consensus oscillation mode parameters; The consensus oscillation mode parameters are associated and encapsulated with the dominant oscillation energy value to form dominant oscillation mode information; If the dominant oscillation energy value in the dominant oscillation mode information is less than a preset trigger threshold, an oscillation-free indicator signal is output. If the dominant oscillation energy value in the dominant oscillation mode information is greater than a preset trigger threshold, output oscillation suppression. activation Signal.

4. The apparatus according to claim 3, characterized in that, The consensus oscillation mode parameters include the consensus oscillation frequency, the consensus oscillation damping ratio, and the consensus oscillation amplitude parameters. The damping compensation unit is specifically used for: Upon receiving the oscillation suppression activation signal, the first oscillation suppression mode is selected; In the first oscillation suppression mode, a synchronous oscillation reference signal is generated based on the consensus oscillation frequency in the consensus oscillation mode parameters; The damping gain coefficient is calculated based on the consensus oscillation amplitude and consensus oscillation damping ratio in the consensus oscillation mode parameters. The damping gain coefficient and the synchronous oscillation reference signal are phase-compensated to generate the corresponding damping current component. Upon receiving a no-oscillation flag signal, select the second oscillation suppression mode and set the damping current component to zero.

5. The apparatus according to claim 1, characterized in that, The compensation module is specifically used for: Receive the damping current component generated by the damping compensation unit; The corresponding reactive power regulation current is calculated based on the time series data to form a reactive current component. The reactive current component and the damping current component are respectively transformed to the synchronous rotating coordinate system through coordinate transformation to obtain the first and second rotating axis components corresponding to the reactive current component, and the third and fourth rotating axis components corresponding to the damping current component. In the synchronous rotating coordinate system, the first rotating axis component of the reactive current component and the third rotating axis component of the damping current component are superimposed to obtain the first rotating axis reference component of the reactive compensation current. The second rotating axis component of the reactive current component is superimposed with the fourth rotating axis component of the damping current component to obtain the second rotating axis reference component of the reactive compensation current. The reactive power compensation current reference is obtained by inverse coordinate transformation of the first and second rotating axis reference components of the reactive power compensation current.

6. The apparatus according to claim 5, characterized in that, The compensation module is also used for: The amplitude of the reactive power compensation current is calculated based on the first rotating axis reference component and the second rotating axis reference component. If the amplitude of the reactive power compensation current is greater than the rated current capacity of the grid-connected power regulation equipment, a limiting factor is calculated, wherein the limiting factor is the ratio of the rated current capacity to the amplitude of the reactive power compensation current. Multiply the first rotation axis reference component and the second rotation axis reference component by the limiting coefficient respectively to obtain the first rotation axis reference component and the second rotation axis reference component after limiting. The first and second rotating axis reference components after amplitude limiting are subjected to inverse coordinate transformation to obtain the reactive power compensation current reference after amplitude limiting.

7. The apparatus according to claim 1, characterized in that, The power electronic execution module is specifically used for: Receive the reactive power compensation current reference output by the compensation module; The reactive power compensation current reference is converted into a corresponding control signal, and the grid-connected power regulation device is driven to output the corresponding compensation current to the grid-connected node according to the control signal.

8. The apparatus according to claim 1, characterized in that, The electrical data acquisition module is specifically used for: The voltage and current signals of the grid-connected nodes are synchronously sampled to obtain voltage and current sequences; The amplitude, phase, and frequency information of the grid voltage are extracted from the voltage sequence to form voltage characteristic quantities; The active power, reactive power, and power factor are calculated based on the voltage sequence and the current sequence to form power characteristic quantities; The voltage sequence, the current sequence, the voltage characteristic, and the power characteristic are encapsulated to form time series data.

9. The apparatus according to claim 1, characterized in that, It also includes a protection module; The protection module is electrically connected to both the electrical acquisition module and the power electronic execution module. The protection module is specifically used to: detect the operating status of the grid-connected node based on the time series data; When an abnormal operating state is detected, a protection trigger signal is generated and transmitted to the power electronic execution module.

10. The apparatus according to claim 9, characterized in that, The power electronic actuator module is also used for: Upon receiving the protection trigger signal, the reactive power compensation current reference is shielded, and the grid-connected power regulation equipment is controlled to perform protection actions according to the protection strategy corresponding to the protection trigger signal.

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