Relay protection analysis method and system for distributed photovoltaic access power distribution network

Abstract

The invention discloses a distributed photovoltaic access power distribution network relay protection analysis method and system, and belongs to the technical field of photovoltaic grid connection, and the method specifically comprises the steps: injecting a dynamic resonance detection signal at the AC side of a current converter of a photovoltaic grid-connected system, and enabling the frequency to be matched with the natural resonance frequency of a target section; analyzing the energy focusing effect of the dynamic resonance detection signal in the power distribution network, and generating a resonance energy distribution map; when the energy density of a certain section in the resonance energy distribution map exceeds a preset threshold value, the photovoltaic output current waveform is adjusted to be a discontinuous waveform containing periodic intermittent cutoff; based on the reflection delay difference of the waveform in the fault section, constructing a space-time mapping model of a fault point, and analyzing and determining a fault position; according to an output result of the space-time mapping model, controlling a photovoltaic side circuit breaker and a power grid side relay to execute a selective tripping action based on waveform phase synchronization; according to the invention, the sensitivity and reliability of distributed photovoltaic access power distribution network relay protection are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid connection, and particularly to a method and system for analyzing relay protection of distributed photovoltaic access to a distribution network. Background Art

[0002] With the wide application of distributed photovoltaic power generation in the distribution network, the topological structure and power flow characteristics of the distribution network have changed significantly. The traditional passive relay protection technology is difficult to meet the requirements of rapid fault detection and accurate isolation in complex operation scenarios. The active detection protection technology emerges as the times require. By actively injecting specific signals into the power grid, the system response characteristics are obtained to identify potential faults, providing a new technical path for relay protection and becoming a research hotspot in the field of intelligent power grid protection.

[0003] The existing active detection protection technologies mainly detect faults by injecting detection signals with a fixed frequency into the distribution network and analyzing the propagation characteristics and reflection characteristics of the signals in the network. Some solutions use the injected harmonic signals to judge the fault location based on the distribution law of harmonic currents; there are also technologies that adopt the pulse injection method to locate faults according to the attenuation and delay characteristics of the pulse signals. These methods have improved the fault detection effect to a certain extent and provided a practical basis for active protection.

[0004] However, the detection signals with a fixed frequency are difficult to adapt to the real-time changing impedance characteristics of the distribution network and cannot form an effective resonance with the natural resonance frequency of a specific section of the power grid, resulting in insufficient extraction of fault signal characteristics; during the fault location process, the dynamic changes of the power grid topological structure and the energy transfer characteristics during the fault development process are not fully considered, and the early warning and effective isolation of faults cannot be achieved, affecting the power supply reliability and operation stability of the distribution network. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for analyzing relay protection of distributed photovoltaic access to a distribution network, and solve the following technical problems: The detection signals with a fixed frequency are difficult to adapt to the real-time changing impedance characteristics of the distribution network and cannot form an effective resonance with the natural resonance frequency of a specific section of the power grid, resulting in insufficient extraction of fault signal characteristics; during the fault location process, the dynamic changes of the power grid topological structure and the energy transfer characteristics during the fault development process are not fully considered, and the early warning and effective isolation of faults cannot be achieved.

[0006] The purpose of the present invention can be achieved by the following technical solutions: A method for analyzing relay protection of distributed photovoltaic access to a distribution network includes the following steps: Inject a dynamic resonance detection signal into the AC side of the converter in the photovoltaic grid-connected system. The frequency of the dynamic resonance detection signal is adaptively adjusted according to the real-time impedance characteristics of the distribution network to match the natural resonance frequency of the target section. Generate a resonance energy distribution map reflecting the fault characteristics by analyzing the energy focusing effect of the dynamic resonance detection signal in the distribution network. When the energy density of a certain section in the resonance energy distribution map exceeds the preset threshold, trigger the fault current reconstruction mode on the photovoltaic side and adjust the photovoltaic output current waveform to a discontinuous waveform including periodic intermittent current interruption. Based on the reflection delay difference of the intermittent current interruption waveform in the fault section, construct a spatio-temporal mapping model of the fault point and determine the fault location by analyzing the spatio-temporal mapping model. According to the output result of the spatio-temporal mapping model, control the photovoltaic side circuit breaker and the grid side relay to perform a selective tripping action based on waveform phase synchronization.

[0007] As a further solution of the present invention: The dynamic resonance detection signal is specifically: Embed a random pulse sequence in the modulation wave of the converter in the photovoltaic grid-connected system. The width of the random pulse sequence is negatively correlated with the current fundamental frequency period of the distribution network. By real-time monitoring the small fluctuations of the distribution network impedance, dynamically adjust the interval time of the random pulse sequence so that the frequency of the dynamic resonance detection signal forms a dynamic envelope around the natural resonance frequency of the distribution network. The frequency coverage range of the dynamic envelope is from the preset low-frequency multiple band to the preset high-frequency multiple band of the distribution network fundamental frequency, and the shape of the dynamic envelope is reshaped in real time according to the voltage harmonic distortion rate of adjacent nodes.

[0008] As a further solution of the present invention: The generation process of the resonance energy distribution map is: Deploy bipolar magnetic field sensors at the beginning and end of each branch line of the distribution network to capture the electromagnetic field vortex characteristics generated when the dynamic resonance detection signal propagates. Extract the magnetic field rotation direction and magnetic field strength gradient information in the electromagnetic field vortex characteristics and calculate the energy absorption coefficient of each line section. Perform three-dimensional correlation on the energy absorption coefficient and the dynamic envelope frequency to generate a three-dimensional map with the frequency dimension, space dimension, and energy density dimension as coordinate axes, and mark the abnormal section with a sudden increase in energy density.

[0009] As a further solution of the present invention: The specific content of the fault current reconstruction mode includes: After detecting a sudden increase in energy density, switch the maximum power point tracking control on the photovoltaic DC side to the chaos modulation mode, and make the photovoltaic output current show intermittent current interruption characteristics by introducing non-linear carrier perturbation. The duration of the intermittent current interruption is positively correlated with the sudden increase amplitude of the energy density, and the interruption interval is synchronized with the dynamic envelope frequency; Meanwhile, a reverse compensation current is superimposed on the AC side of the converter in the PV grid-connected system, so that the electromagnetic transient wave generated at the moment of current interruption forms a traceable reflection mark.

[0010] As a further solution of the present invention: The construction method of the spatio-temporal mapping model is as follows: Using the reflection time difference of the electromagnetic transient wave at the moment of current interruption between the fault section and the non-fault section, calculate the equivalent electrical distance of the propagation path of the electromagnetic transient wavefront; by comparing the drift amount of the equivalent electrical distance in different current interruption periods, identify the dynamic displacement trajectory of the fault point; match the dynamic displacement trajectory with the preset grid topology time-delay database to determine the physical grid coordinates where the fault point is located.

[0011] As a further solution of the present invention: The specific logic of the selective tripping action based on waveform phase synchronization is as follows: After the physical grid coordinates of the fault point are determined, extract the voltage phase change characteristics of the grid nodes corresponding to the physical grid coordinates in the nearest preset number of fundamental frequency periods; Control the pre-breakdown operation of the PV side circuit breaker within a preset angle range before the voltage phase passes through the zero point, and artificially create a local arc to enhance the fault characteristics; Synchronously adjust the action timing of the grid side relay so that the tripping moment of the grid side relay is strictly aligned with the electromagnetic radiation peak value of the pre-breakdown arc, realizing the spatio-temporal focusing of the protection action.

[0012] As a further solution of the present invention: The specific content of the pre-breakdown operation includes: Within a preset angle range before the voltage phase passes through the zero point, inject a high-frequency induced current into the contacts of the PV side circuit breaker to ionize the medium between the contacts in advance; according to the electrical properties of the physical grid coordinates of the fault point, dynamically adjust the amplitude gradient of the high-frequency induced current to make the ionization intensity match the severity of the fault; record the optical signal spectrum characteristics during the ionization process as the basis for secondary verification of the fault type.

[0013] As a further solution of the present invention: After the first tripping action is completed, inject a low-frequency scanning signal into the isolated section and monitor the harmonic regeneration phenomenon of the low-frequency scanning signal in the adjacent section; By analyzing the frequency offset and amplitude attenuation slope of the harmonic regeneration signal, construct a fault energy transfer chain model; when the fault energy transfer chain model shows that the length of the energy transfer chain exceeds the preset safety value, automatically start the whole network impedance reshaping program to forcefully change the resonance frequency distribution of the non-fault section.

[0014] As a further solution of the present invention: The whole-network impedance reshaping program specifically includes: By coordinating the output phases of the converters of the photovoltaic grid-connected system and the energy storage device, a controllable standing-wave interference phenomenon is artificially created in the distribution network; the position of the standing-wave antinode is adjusted to cover the key nodes of the fault energy transfer chain, and the low-impedance characteristics of the node region are used to absorb the residual fault energy; after the absorption of the residual fault energy is completed, the original frequency distribution of the distribution network is gradually restored, and the stability of the distribution network is verified by the full-frequency band scanning of the dynamic resonance detection signal.

[0015] The present invention further includes a distributed photovoltaic access distribution network relay protection analysis system for implementing the above-mentioned distributed photovoltaic access distribution network relay protection analysis method, including: A signal injection module for injecting a dynamic resonance detection signal into the AC side of the converter of the photovoltaic grid-connected system, and the frequency of the dynamic resonance detection signal is adaptively adjusted according to the real-time impedance characteristics of the distribution network to match the natural resonance frequency of the target section; A spectrum generation module for generating a resonance energy distribution spectrum reflecting the fault characteristics by analyzing the energy focusing effect of the dynamic resonance detection signal in the distribution network; A waveform adjustment module for triggering the fault current reconstruction mode on the photovoltaic side and adjusting the photovoltaic output current waveform to a discontinuous waveform including periodic intermittent current interruption when the energy density of a certain section in the resonance energy distribution spectrum exceeds a preset threshold; A fault location module for constructing a spatio-temporal mapping model of the fault point based on the reflection delay difference of the intermittent current interruption waveform in the fault section, and analyzing and determining the fault location through the spatio-temporal mapping model; A tripping control module for controlling the photovoltaic side circuit breaker and the grid side relay to perform a selective tripping action based on waveform phase synchronization according to the output result of the spatio-temporal mapping model.

[0016] The beneficial effects of the present invention: The present invention injects a frequency - adaptive dynamic resonance detection signal on the AC side of the converter in the photovoltaic grid - connected system to match the natural resonance frequency of the target section, and uses the energy focusing effect to generate a resonance energy distribution map, so as to solve the problems that traditional fixed - frequency detection signals are difficult to adapt to grid impedance changes and the lack of extraction of fault signal characteristics; when the energy density in the map exceeds the threshold, it triggers the photovoltaic - side fault current reconstruction mode, adjusts the output current to a discontinuous waveform with periodic intermittent current interruption, and superimposes a reverse compensation current to form a reflection mark to enhance the recognition of fault characteristics; based on the reflection delay difference of the intermittent current - interruption waveform in the fault section, a spatio - temporal mapping model is constructed, and combined with the grid topology time - delay database to determine the fault location, overcoming the defect that the existing methods cannot consider the dynamic changes of the grid topology; by controlling the pre - breakdown operation of the photovoltaic - side circuit breaker and the action timing of the grid - side relay, selective tripping based on waveform phase synchronization is realized to solve the problem of inaccurate fault removal; after the first tripping, a low - frequency scanning signal is injected to construct a fault energy transfer chain model, and a whole - network impedance reshaping program is started to change the resonance frequency distribution, absorb the residual fault energy, avoid fault spread, and comprehensively improve the sensitivity, accuracy and reliability of the relay protection for distributed photovoltaic access to the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the drawings.

[0018] Figure 1 It is a schematic flow chart of the relay protection analysis method for distributed photovoltaic access to the distribution network of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.

[0020] Please refer to Figure 1 As shown, the present invention is a relay protection analysis method for distributed photovoltaic access to the distribution network, including the following steps: First, a dynamic resonance detection signal is injected into the AC side of the converter in the PV grid-connected system. The system monitors the impedance change of the distribution network in real time and uses an adaptive frequency adjustment algorithm to dynamically adjust the frequency of the detection signal. Specifically, by calculating the natural resonance frequencies of each section of the distribution network online, the frequency of the injected dynamic resonance detection signal is precisely matched with the target section. In actual operation, a random pulse sequence is embedded in the modulation wave of the converter in the PV grid-connected system. The width of this sequence is negatively correlated with the current fundamental frequency period of the distribution network. By tracking the minute fluctuations of the distribution network impedance in real time, the interval time of the random pulse sequence is dynamically adjusted, enabling the detection signal frequency to form a dynamic envelope around the natural resonance frequency of the distribution network. The frequency coverage range of this envelope is from the preset low-frequency multiple band to the preset high-frequency multiple band of the fundamental frequency of the distribution network, and the envelope shape is reshaped in real time according to the voltage harmonic distortion rate of adjacent nodes, thus ensuring that the detection signal can effectively stimulate the resonance effect of the power grid.

[0021] Next, with the help of bipolar magnetic field sensors deployed at the heads and ends of each branch line of the distribution network, the electromagnetic field vortex characteristics generated during the propagation of the dynamic resonance detection signal are captured. The magnetic field rotation direction and magnetic field intensity gradient information in the electromagnetic field vortex characteristics are extracted, and an energy analysis algorithm is used to calculate the energy absorption coefficient of each line section. Subsequently, the energy absorption coefficient is three-dimensionally correlated with the dynamic envelope frequency to generate a three-dimensional resonance energy distribution map with the frequency dimension, spatial dimension, and energy density dimension as the coordinate axes. The map can visually present the energy distribution state of the detection signal in the power grid and automatically mark the abnormal sections with sudden increases in energy density, providing a visual basis for fault judgment.

[0022] Once the energy density of a certain section in the resonance energy distribution map exceeds the preset threshold, the system immediately triggers the fault current reconstruction mode on the PV side. At this time, the maximum power point tracking control on the PV DC side is switched to the chaotic modulation mode. By introducing a non-linear carrier perturbation, the PV output current exhibits intermittent current interruption characteristics. Among them, the duration of the intermittent current interruption is positively correlated with the amplitude of the sudden increase in energy density, and the interruption interval is synchronized with the dynamic envelope frequency. At the same time, a reverse compensation current is superimposed on the AC side of the converter in the PV grid-connected system, making the electromagnetic transient wave generated at the moment of current interruption form a traceable reflection mark, further enhancing the fault characteristics.

[0023] Then, based on the reflection delay differences of the intermittent current interruption waveform between the fault section and the non-fault section, a spatio-temporal mapping model of the fault point is constructed. Using the reflection time difference of the electromagnetic transient wave generated at the moment of current interruption in different sections, the equivalent electrical distance of the propagation path of the electromagnetic transient wavefront is calculated. By comparing the drift amount of the equivalent electrical distance within different current interruption periods, the dynamic displacement trajectory of the fault point is identified. Then, the dynamic displacement trajectory is matched with the preset grid topology time-delay database, thereby accurately determining the physical grid coordinates where the fault point is located.

[0024] Finally, based on the physical grid coordinates of the fault point output by the spatio-temporal mapping model, the system extracts the voltage phase change characteristics of the power grid node corresponding to this coordinate within the recent preset number of fundamental frequency cycles. The photovoltaic side circuit breaker is controlled to perform a pre-breakdown operation within a preset angle range before the voltage phase zero crossing, injecting a high-frequency induced current into the circuit breaker contacts to pre-ionize the dielectric in the contact gap. According to the electrical properties of the physical grid coordinates of the fault point, the amplitude gradient of the high-frequency induced current is dynamically adjusted to match the ionization intensity with the severity of the fault. At the same time, the action timing of the grid side relay is synchronously adjusted to strictly align the tripping moment of the grid side relay with the peak value of the electromagnetic radiation of the pre-breakdown arc, realizing a selective tripping action based on waveform phase synchronization, quickly and accurately isolating the fault section, and ensuring the safe and stable operation of the distribution network.

[0025] In a preferred embodiment of the present invention, the dynamic resonance detection signal is specifically: The dynamic resonance detection signal adopts an innovative pulse sequence modulation strategy to achieve deep coupling with the state of the distribution network. Specifically, a random pulse sequence is embedded in the modulation wave of the converter in the photovoltaic grid-connected system. The width of this sequence follows a strict negative correlation mechanism - it is linked in real-time with the current fundamental frequency cycle of the distribution network. When the fundamental frequency cycle shortens, the pulse becomes narrower; conversely, it becomes wider, ensuring that the signal has dynamic adaptability. The system is equipped with a high-precision impedance monitoring module to capture the subtle fluctuations of the distribution network impedance at a millisecond-level sampling frequency. Through an adaptive timing adjustment algorithm, the interval time of the random pulse sequence is dynamically changed. This adjustment process is based on the real-time measurement of the natural resonance frequency of the distribution network, making the frequency of the detection signal form a dynamically changing frequency envelope centered on the natural resonance frequency. The frequency range of this envelope covers the preset low-frequency multiple band to the high-frequency multiple band of the fundamental frequency of the distribution network (such as the 0.5 - 3 times fundamental frequency interval), and its shape is not fixed, but is reshaped in real-time according to the voltage harmonic distortion rate of adjacent nodes. When the distortion rate increases, the envelope automatically expands to enhance the signal coverage ability; when the distortion rate decreases, it contracts and focuses to improve the energy density, ensuring that the detection signal always excites the grid resonance effect in the optimal form.

[0026] In another preferred embodiment of the present invention, the generation of the resonance energy distribution map relies on multi-dimensional electromagnetic feature capture and three-dimensional modeling technology. Bipolar magnetic field sensor arrays are deployed at key nodes (the head and the end) of each branch line of the distribution network. The sensors adopt the composite sensing technology of fluxgate and Hall effect, and can simultaneously detect the dynamic changes of the magnetic field intensity and direction, accurately capturing the electromagnetic field vortex characteristics generated during the propagation of the dynamic resonance detection signal. The sensor data is processed in real time by the edge computing unit to extract the magnetic field rotation direction (clockwise / counterclockwise) and the magnetic field intensity gradient information, where the gradient information reflects the energy attenuation rate in space. Based on the electromagnetic field theory, an energy absorption coefficient calculation model is established, incorporating parameters such as the magnetic field intensity change rate and the rotation angular velocity into the calculation to obtain the energy absorption coefficients of each line section. Subsequently, a three-dimensional data mapping algorithm is used to correlate the energy absorption coefficient, the dynamic envelope frequency, and the line space coordinates. With the frequency as the vertical axis, the spatial position as the horizontal and vertical plane, and the energy density as the color / height encoding, an intuitive three-dimensional map is generated. The map has an intelligent marking function. When the energy density in a certain area exceeds the threshold set based on historical data and operation experience, the abnormal section is automatically highlighted and marked, providing a visual basis for fault location.

[0027] In another preferred embodiment of the present invention, the specific content of the fault current reconstruction mode includes: The fault current reconstruction mode adopts a dual reinforcement mechanism of chaotic modulation and electromagnetic marking. After the system detects a sudden increase in the energy density in the resonance energy distribution map, it immediately initiates the switching of the photovoltaic DC side control strategy, converting the conventional maximum power point tracking control into the chaotic modulation mode. This mode makes the photovoltaic output current exhibit periodic intermittent current interruption characteristics by introducing a non-linear carrier perturbation algorithm. The duration of the current interruption is strictly positively correlated with the amplitude of the sudden increase in the energy density. For example, when the energy density increases by 10%, the current interruption time is extended by 20%. The current interruption interval is synchronized and phase-locked with the dynamic envelope frequency to ensure that the current interruption period coordinates with the frequency change of the detection signal. At the same time, a reverse compensation current injection module is deployed on the AC side of the converter in the photovoltaic grid-connected system. This module calculates the characteristics of the electromagnetic transient wave generated at the moment of current interruption based on the fault transient analysis model and generates a matching reverse compensation current. After the compensation current is injected, it is superimposed with the current interruption transient wave to form a unique reflection mark, which contains the characteristic encoding of frequency, phase, and amplitude, facilitating the subsequent accurate identification of the fault location through the traveling wave analysis technology, and significantly improving the recognizability of the fault characteristics and the positioning accuracy.

[0028] In another preferred embodiment of the present invention, the construction method of the spatio-temporal mapping model is: The process of constructing the spatio-temporal mapping model integrates electromagnetic transient analysis and dynamic trajectory matching technology to achieve high-precision positioning of the fault point. The system captures in real time the electromagnetic transient wave generated at the moment of intermittent interruption of the photovoltaic output current. Through transient monitoring devices deployed at key nodes of the distribution network, the reflected signals of the transient wave in the fault section and the non-fault section are collected. Based on the traveling wave transmission theory, using the reflection time difference between different sections and combining the line parameters and wave velocity calculation model, the equivalent electrical distance of the propagation path of the electromagnetic transient wavefront is accurately calculated. Considering factors such as the dynamic change of the arc and the fluctuation of line parameters during the fault development process, the system continuously monitors multiple interruption cycles, compares the drift amount of the equivalent electrical distance in different cycles, smooths the data through the Kalman filter algorithm, and identifies the dynamic displacement trajectory of the fault point over time. At the same time, a time-delay database containing information such as the power grid topology structure, line length, and impedance parameters is established, and the dynamic displacement trajectory is pattern-matched with the theoretical time-delay data in the database. An optimization algorithm is used to solve the optimal matching solution, and finally the physical grid coordinates where the fault point is located are determined, and the error can be controlled within 10% of the actual line node spacing.

[0029] In another preferred embodiment of the present invention, the specific logic of the selective tripping action based on waveform phase synchronization is as follows: The selective tripping action based on waveform phase synchronization adopts a multi-link collaborative control strategy to improve the efficiency and accuracy of fault isolation. After the physical grid coordinates of the fault point are determined, the system immediately retrieves the real-time monitoring data of the power grid node corresponding to this coordinate, extracts the voltage phase change characteristics within the nearest preset number (such as 5 - 10) of fundamental frequency cycles, and realizes high-precision phase tracking through the phase-locked loop technology. For the photovoltaic-side circuit breaker, within a preset angle range (such as 15° - 30°) before the voltage phase is about to cross zero, the pre-breakdown operation procedure is triggered. This procedure injects a high-frequency induced current into the circuit breaker contacts through a dedicated control module, and the current frequency is set from several kilohertz to dozens of kilohertz. The skin effect is used to accelerate the ionization of the dielectric in the contact gap. At the same time, according to the electrical attributes such as the line voltage level and the calculated value of the short-circuit current associated with the physical grid coordinates of the fault point, the amplitude gradient of the high-frequency induced current is dynamically adjusted. For example, for faults with a high voltage level and a large short-circuit current, the current amplitude is automatically increased to enhance the ionization intensity, so that the ionization degree is accurately matched with the severity of the fault.

[0030] In a preferred case of this embodiment, the specific content of the pre-breakdown operation includes: During the implementation of the pre-breakdown operation, the spectral monitoring equipment deployed near the circuit breaker by the system records the optical signals generated by the ionization of the contact gap in real time, and analyzes the spectral characteristics of the optical signals through spectral analysis technology. Different fault types (such as metallic short circuit, arcing ground short circuit) will generate optical signals with specific spectral fingerprints during the ionization process. The system compares the collected spectral characteristics with the preset fault spectral database as the basis for secondary verification of the fault type, effectively reducing the risk of protection misoperation. At the same time, according to the characteristics of the electromagnetic radiation signals generated by the pre-breakdown arc, the relay control unit on the grid side adjusts the action time of the relay through an accurate timing control algorithm to ensure that its tripping action is strictly aligned with the peak value of the electromagnetic radiation of the pre-breakdown arc. This spatio-temporal focused protection action strategy can shorten the fault isolation time to within several fundamental frequency cycles, significantly reducing the impact range and duration of the fault on the distribution network.

[0031] In another preferred embodiment of the present invention, to prevent the spread of fault energy from triggering a chain reaction, after the first tripping action is completed and the fault section is successfully isolated, the system immediately activates the secondary monitoring and active defense mechanism. A low-frequency scanning signal is injected into the isolated section through an intelligent signal injection device, and the signal frequency is set outside the normal operating frequency range of the distribution network (such as 5-20 Hz) to avoid interference with normal operating signals. The broadband monitoring sensors deployed along the line capture in real time the harmonic regeneration phenomenon of the low-frequency scanning signal during propagation in the adjacent section - that is, the frequency component variation of the signal due to factors such as abnormal line parameters and electromagnetic coupling.

[0032] The system uses time-frequency analysis algorithms to deeply analyze the harmonic regeneration signals, accurately calculate the frequency offset (the difference between the actual frequency and the injected frequency) and the amplitude attenuation slope (the attenuation rate of the signal amplitude with the propagation distance) of the signals. Based on these characteristic parameters, combined with the distribution network topology and line electrical parameters, a fault energy transfer chain model is constructed. This model visually presents the propagation path and intensity change of the fault energy in the network in a graphical form, with each node representing a key position in the power grid and the connection lines indicating the energy transfer direction and intensity. When the length of the energy transfer chain calculated by the model exceeds the preset safety value set according to factors such as the power grid scale and equipment tolerance, the system determines that there is a risk of fault spread and immediately triggers the whole-network impedance reshaping program.

[0033] In a preferred case of this embodiment, the whole-network impedance reshaping program specifically includes: During the implementation of the full-domain impedance reshaping program, the system collaboratively controls the output phase of the inverter and energy storage device of the photovoltaic grid-connected system through the energy management platform. By utilizing the rapid regulation capability of power electronic equipment, a controllable standing wave interference phenomenon is artificially created in the distribution network. By accurately calculating the output phase and amplitude of each device, the antinode position of the standing wave accurately covers the key nodes of the fault energy transfer chain, that is, the hub position or weak link of energy transmission. The node area can efficiently absorb residual fault energy due to its low impedance characteristics, blocking the fault propagation path like an "energy trap".

[0034] During the residual fault energy absorption process, the system continuously monitors the voltage, current waveform and energy flow data of each node. When it detects that the abnormal energy level in the network has dropped below the safety threshold, the frequency recovery program is started. The program gradually adjusts the output parameters of photovoltaic and energy storage equipment in a progressive manner to restore the frequency distribution of the distribution network to its original operating state. After the recovery is completed, the system injects a full-band dynamic resonance detection signal again to scan the entire distribution network. By analyzing the propagation characteristics, energy distribution and network response of the detection signal, the operating stability and fault defense capabilities of the distribution network are verified to ensure that the power grid is restored to a safe and reliable operating state.

[0035] The present invention also includes a distributed photovoltaic access distribution network relay protection analysis system, which is used to implement the above-mentioned distributed photovoltaic access distribution network relay protection analysis method, including: A signal injection module is used to inject a dynamic resonance detection signal on the AC side of the inverter of the photovoltaic grid-connected system, wherein the frequency of the dynamic resonance detection signal is adaptively adjusted according to the real-time impedance characteristics of the distribution network so that the frequency matches the natural resonance frequency of the target section; A spectrum generation module, used to generate a resonance energy distribution spectrum reflecting fault characteristics by analyzing the energy focusing effect of the dynamic resonance detection signal in the distribution network; A waveform adjustment module is used to trigger the fault current reconstruction mode on the photovoltaic side when the energy density of a certain section in the resonance energy distribution spectrum exceeds a preset threshold, and adjust the photovoltaic output current waveform to a non-continuous waveform including periodic intermittent current interruption; The fault location module is used to construct a time-space mapping model of the fault point based on the reflection delay difference of the intermittent current interruption waveform in the fault section, and determine the fault location through the time-space mapping model analysis; The tripping control module is used to control the photovoltaic side circuit breaker and the grid side relay to perform a selective tripping action based on waveform phase synchronization according to the output result of the time-space mapping model.

[0036] The above has described in detail an embodiment of the present invention, but the above content is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made in accordance with the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. Analysis method for relay protection of distributed photovoltaic power access to distribution network, characterized in that Including the following steps: Inject a dynamic resonance detection signal into the AC side of the converter in the photovoltaic grid-connected system. The frequency of the dynamic resonance detection signal is adaptively adjusted according to the real-time impedance characteristics of the distribution network, so that the frequency matches the natural resonance frequency of the target section; Generate a resonance energy distribution map reflecting the fault characteristics by analyzing the energy focusing effect of the dynamic resonance detection signal in the distribution network; When the energy density of a certain section in the resonance energy distribution map exceeds a preset threshold, trigger the fault current reconstruction mode on the photovoltaic side, and adjust the photovoltaic output current waveform to a discontinuous waveform including periodic intermittent current interruption; Based on the reflection delay difference of the intermittent current interruption waveform in the fault section, construct a spatio-temporal mapping model of the fault point, and determine the fault location by analyzing the spatio-temporal mapping model; According to the output result of the spatio-temporal mapping model, control the photovoltaic side circuit breaker and the grid side relay to perform a selective tripping action based on waveform phase synchronization.

2. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, wherein The specific form of the dynamic resonance detection signal is: Embed a random pulse sequence in the modulation wave of the converter in the photovoltaic grid-connected system. The width of the random pulse sequence is negatively correlated with the current fundamental frequency period of the distribution network; By real-time monitoring the small fluctuations of the distribution network impedance, dynamically adjust the interval time of the random pulse sequence, so that the frequency of the dynamic resonance detection signal forms a dynamic envelope around the natural resonance frequency of the distribution network; The frequency coverage range of the dynamic envelope is from a preset low-frequency multiple band to a preset high-frequency multiple band of the distribution network fundamental frequency, and the shape of the dynamic envelope is reshaped in real time according to the voltage harmonic distortion rate of adjacent nodes.

3. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, wherein The generation process of the resonance energy distribution map is: Deploy bipolar magnetic field sensors at the head and end of each branch line of the distribution network to capture the electromagnetic field vortex characteristics generated when the dynamic resonance detection signal propagates; Extract the magnetic field rotation direction and magnetic field intensity gradient information in the electromagnetic field vortex characteristics, and calculate the energy absorption coefficient of each line section; Perform three-dimensional correlation on the energy absorption coefficient and the dynamic envelope frequency, generate a three-dimensional map with the frequency dimension, space dimension and energy density dimension as the coordinate axes, and mark the abnormal section with a sudden increase in energy density.

4. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, characterized in that, The specific content of the fault current reconstruction mode includes: After detecting a sudden increase in energy density, switch the maximum power point tracking control on the photovoltaic DC side to a chaotic modulation mode, and make the photovoltaic output current show intermittent current interruption characteristics by introducing non-linear carrier perturbation; The duration of the intermittent current interruption is positively correlated with the amplitude of the sudden increase in energy density, and the current interruption interval is synchronized with the dynamic envelope frequency; At the same time, superimpose a reverse compensation current on the AC side of the converter in the photovoltaic grid-connected system, so that the electromagnetic transient wave generated at the moment of current interruption forms a traceable reflection mark.

5. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, characterized in that The construction method of the spatio-temporal mapping model is: Use the reflection time difference of the electromagnetic transient wave at the moment of current interruption in the fault section and the non-fault section to calculate the equivalent electrical distance of the electromagnetic transient wavefront propagation path; by comparing the drift amount of the equivalent electrical distance in different current interruption periods, identify the dynamic displacement trajectory of the fault point; match the dynamic displacement trajectory with the preset grid topology time delay database to determine the physical grid coordinates where the fault point is located.

6. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, characterized in that The specific logic of the selective tripping operation based on waveform phase synchronization is as follows: After determining the physical grid coordinates of the fault point, extract the voltage phase change characteristics of the grid nodes corresponding to the physical grid coordinates within the nearest preset number of fundamental frequency cycles; Control the photovoltaic side circuit breaker to perform a pre-breakdown operation within a preset angle range before the voltage phase zero crossing, artificially creating a local arc to enhance the fault characteristics; Synchronously adjust the action timing of the grid side relay so that the tripping moment of the grid side relay is strictly aligned with the electromagnetic radiation peak of the pre-breakdown arc, realizing the spatio-temporal focusing of the protection action.

7. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 6, characterized in that The specific content of the pre-breakdown operation includes: Within a preset angle range before the voltage phase zero crossing, inject a high-frequency induced current into the contacts of the photovoltaic side circuit breaker to pre-ionize the dielectric in the contact gap; according to the electrical properties of the physical grid coordinates of the fault point, dynamically adjust the amplitude gradient of the high-frequency induced current so that the ionization intensity matches the severity of the fault; record the optical signal spectrum characteristics during the ionization process as the basis for secondary verification of the fault type.

8. The relay protection analysis method for distributed photovoltaic power access to the distribution network according to claim 1, wherein After the first tripping operation is completed, inject a low-frequency scanning signal into the isolated section and monitor the harmonic regeneration phenomenon of the low-frequency scanning signal in the adjacent section; By analyzing the frequency offset and amplitude attenuation slope of the harmonic regeneration signal, construct a fault energy transfer chain model; when the fault energy transfer chain model shows that the length of the energy transfer chain exceeds the preset safety value, automatically start the whole network impedance reshaping program to forcibly change the resonance frequency distribution of the non-fault section.

9. The relay protection analysis method for distributed PV access to the distribution network according to claim 8, wherein, The specific content of the whole network impedance reshaping program includes: By coordinating the output phases of the converters and energy storage devices in the photovoltaic grid-connected system, artificially create a controllable standing wave interference phenomenon in the distribution network; adjust the position of the standing wave antinode to cover the key nodes of the fault energy transfer chain, and use the low impedance characteristics of the node area to absorb the residual fault energy; after the absorption of the residual fault energy is completed, gradually restore the original frequency distribution of the distribution network and verify the stability of the distribution network through the full-frequency band scanning of the dynamic resonance detection signal.

10. A relay protection analysis system for distributed photovoltaic power access to the distribution network, which is used to implement a relay protection analysis method for distributed photovoltaic power access to the distribution network according to any one of claims 1-9, characterized in that, It includes: A signal injection module for injecting a dynamic resonance detection signal into the AC side of the converter in the photovoltaic grid-connected system, and the frequency of the dynamic resonance detection signal is adaptively adjusted according to the real-time impedance characteristics of the distribution network to match the natural resonance frequency of the target section; A spectrum generation module for generating a resonance energy distribution spectrum reflecting the fault characteristics by analyzing the energy focusing effect of the dynamic resonance detection signal in the distribution network; A waveform adjustment module for triggering the fault current reconstruction mode on the photovoltaic side when the energy density of a certain section in the resonance energy distribution spectrum exceeds the preset threshold, and adjusting the photovoltaic output current waveform to a discontinuous waveform including periodic intermittent current interruption; A fault location module for constructing a spatio-temporal mapping model of the fault point based on the reflection delay difference of the intermittent current interruption waveform in the fault section, and analyzing and determining the fault location through the spatio-temporal mapping model; A tripping control module for controlling the photovoltaic side circuit breaker and the grid side relay to perform a selective tripping operation based on waveform phase synchronization according to the output result of the spatio-temporal mapping model.

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