Fault analysis method and system for distributed power supply access distribution network

Abstract

The invention provides a fault analysis method and system for a distributed power supply access distribution network, and relates to the technical field of intelligent power grid and distributed power supply access, and the method comprises the steps: building a simulation model: building an AC / DC hybrid power distribution network model containing a distributed power supply on simulation software; fault characteristic analysis: analyzing the change of the fault characteristics of the power distribution network after the distributed power supply is connected; fault injection and simulation: injecting different types of faults into the AC / DC hybrid power distribution network model; fault signal extraction: extracting parameters through simulation data; verification of a protection strategy: verifying the effectiveness of the protection strategy in the AC / DC hybrid power distribution network model; and performance evaluation: based on the generalized S transformation and the Pearson's correlation coefficient, evaluating the reliability in fault identification and protection actions after the distributed power supply is accessed, analyzing the influence of the access of the distributed power supply on the power failure time and the power failure frequency of the system by adopting a sequential Monte Carlo simulation method, and finally realizing accurate identification of the change of the power distribution network fault.

Description

Technical Field

[0001] The present invention relates to the field of smart grid and distributed power supply access technology, and in particular to a fault analysis method and system for distributed power supply access to a distribution network. Background Art

[0002] With the decreasing supply of traditional energy and the increasing environmental pollution, the development and utilization of new and renewable energy has become an inevitable trend in global energy development. Distributed power sources (such as photovoltaic, wind power generation, energy storage devices, etc.) have been widely used and promoted due to their clean, efficient, and flexible characteristics. However, with the access of a large number of distributed power sources to the distribution network, especially the AC / DC hybrid distribution network, the structure and operating characteristics of the distribution network have changed significantly, bringing new challenges to traditional relay protection and fault analysis methods.

[0003] In traditional AC distribution networks, the relay protection system is mainly based on the power frequency phasor protection algorithm, and adopts protection strategies such as three-stage current protection and power direction elements, which can effectively identify and isolate faults. However, the access of distributed power sources has transformed the distribution network from a single power supply to a complex network with multiple power supplies, and the fault characteristics have also changed fundamentally. For example, DC side faults (such as short circuit faults and ground faults) show completely different characteristics from AC systems in terms of abnormal voltage changes and fluctuations in fault current amplitude; there are also significant differences in the performance of island effects in AC systems and DC sides. In addition, the dynamic response characteristics, nonlinear characteristics, and diversity of access methods of distributed power sources (such as direct access, access through transformers, and access through converters) further increase the complexity of fault analysis.

[0004] In the existing technology, the fault analysis methods for distribution networks containing distributed power sources mainly focus on the study of single fault types, and lack comprehensive analysis of multiple fault types in AC / DC hybrid distribution networks (such as short-circuit faults and ground faults on the AC side, short-circuit faults and ground faults on the DC side, and islanding effect faults). In addition, the existing methods fail to fully consider the bidirectionality of the fault impact range after the distributed power source is connected, the dynamic response characteristics, and the impact of non-periodic components and amplitude fluctuations in the fault current on the action of the protection device. This causes the traditional protection strategy to malfunction or refuse to operate in the distribution network after the distributed power source is connected, which seriously affects the power supply reliability and stability of the distribution network. Summary of the invention

[0005] The present invention provides a fault analysis method and system for distributed power supply access to a distribution network, which are used to solve the technical problem in the prior art that changes in distribution network fault characteristics after the distributed power supply access cannot be accurately identified.

[0006] On the one hand, the present invention provides a method for analyzing a fault of a distributed power supply connected to a distribution network, comprising: Establish a simulation model: Build an AC / DC hybrid distribution network model containing distributed power sources on the simulation software; Fault feature analysis: Analyze the changes in distribution network fault features after the distributed generation is connected, including changes in fault type, fault impact range, and fault current characteristics; Fault injection and simulation: different types of faults are injected into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and responses under various fault conditions are recorded; Fault signal extraction: Extract parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in fault current; Protection strategy verification: verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model; Performance evaluation: Based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the access of distributed generation is evaluated, and the impact of the access of distributed generation on the power outage time and frequency of the system is analyzed by using the sequential Monte Carlo simulation method; Among them, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, including: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

[0007] Optionally, the change in the fault type includes the manifestation of a short circuit fault on the DC side, the abnormal voltage change of a ground fault on the DC side, and the difference in islanding effect between the AC system and the DC side; the fault impact range includes the bidirectional impact and dynamic response characteristics caused by the access of distributed power sources; the fault current characteristics include non-periodic components and amplitude fluctuations, and the fault feature analysis includes: The analysis of short-circuit faults includes identifying the manifestations of short-circuit faults on the DC side, including but not limited to the characteristics of short-circuit faults between photovoltaic inverters or energy storage devices, and analyzing the differences between short-circuit faults and AC system short-circuit faults; The analysis of ground faults includes analyzing the characteristics of ground faults on the DC side as an increase or decrease in voltage to ground, and the impact of voltage changes on the system; The analysis of the islanding effect includes simulating the action behavior of the distributed generation when the main power grid fails, evaluating the effectiveness of the islanding detection and protection strategy, analyzing the impact of the islanding state on the AC system and the DC side, and the protection measures taken to avoid the islanding effect; In the fault impact range analysis, the bidirectional impact analysis includes analyzing the phenomenon that the fault impact range spans both the AC and DC systems after the distributed power supply is connected, analyzing the impact of this phenomenon on the fault location time, and measures to reduce the fault location time; Dynamic response analysis includes analyzing the impact of the response characteristics of the distributed power grid-connected inverter on the fault development process and recovery speed, and analyzing the relationship between the dynamic adjustment of the inverter and the amplitude and phase of the fault current; The non-periodic component analysis includes analyzing the content and changes of harmonic components in the fault current caused by the nonlinear characteristics of the distributed power inverter, and analyzing the impact of different distributed power types on the harmonic content; Amplitude fluctuation analysis includes analyzing the characteristics of fault current amplitude fluctuation caused by the dynamic response characteristics of distributed power sources, analyzing the impact of this fluctuation on the action of protection devices and improvement measures.

[0008] Optionally, the fault injection and simulation includes: Simulate the behavior of distributed power sources when they fail under different access modes and analyze their impact on system stability; Inject transient faults of different intensities and durations into AC / DC hybrid distribution networks and analyze their impact on the system dynamic response and protection device operation; Simulate the behavior of distributed power sources when they fail under different environmental conditions and analyze their impact on the fault characteristics; Inject compound faults and analyze their impact on the system protection strategy.

[0009] Optionally, the simulation of the behavior of the distributed power source when a fault occurs in different access modes includes: Constructing an access model for distributed power sources, wherein the access modes of the access model include but are not limited to direct access, access through a transformer, and access through a converter; A fault point is set in the AC / DC hybrid distribution network model, and short circuit fault, ground fault or islanding fault is injected into the AC side and DC side respectively; Analyze the impact of different access methods on system stability; The method of injecting transient faults of different intensities and durations into the AC / DC hybrid distribution network includes: Select fault nodes in the AC / DC hybrid distribution network model and set transient faults of different intensities and durations; Inject transient faults into the AC side and DC side respectively; Analyze the impact of transient faults on system dynamic response and protection device action; The simulated behavior of the distributed power supply when a fault occurs under different environmental conditions includes: Setting environmental parameters of distributed power sources in the AC / DC hybrid distribution network model, including but not limited to the light intensity of the photovoltaic power source, the wind speed of the wind turbine generator, and the charging and discharging status of the energy storage system; Simulate the operating status of distributed power sources under different environmental parameters, inject faults into the AC and DC sides respectively and record the system response; Analyze the impact of environmental parameter changes on fault characteristics; The injection of compound faults and analysis of their impact on the system protection strategy include: Set up compound faults in the AC / DC hybrid distribution network model; Set different fault locations and fault occurrence sequences on the AC side and DC side to simulate compound fault scenarios; Analyze the impact of compound faults on protection strategies.

[0010] Optionally, calculating the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode includes: According to the preset fault mode library and historical simulation data, the correlation coefficient thresholds of different fault types and fault locations are set; For each fault characteristic quantity, calculate the Pearson correlation coefficient between it and the preset fault mode; The method of judging the fault type and location according to the threshold of the Pearson correlation coefficient and verifying the accuracy of the action of the longitudinal protection after the distributed power source is connected includes: According to the comparison result of the correlation coefficient and the correlation coefficient threshold, the fault type and the fault location are determined; According to the determined fault type and fault location, simulate the action logic of the longitudinal protection to obtain the simulated action time and action range; The determined fault type, fault location, simulated action time and action range are compared with the preset fault type, fault location, action time and action range to verify the action accuracy of the longitudinal protection after the distributed power source is connected.

[0011] Optionally, performing a generalized S transform on the fault signal to obtain a transformed fault feature quantity includes: Preprocessing the fault signal; wherein the preprocessing includes filtering and denoising; The preprocessed fault signal is subjected to generalized S transform to decompose the fault signal into information in two dimensions, time and frequency, while retaining the amplitude and phase to obtain the transformed fault feature quantity.

[0012] Optionally, a sequential Monte Carlo simulation method is used to analyze the impact of the access of distributed generation on the system outage time and frequency, including: Initialize system models and parameters, including but not limited to distributed generation characteristics, load demand, grid structure, and protection device settings; Based on the preset failure modes and operating conditions, a series of random event sequences are generated using the sequential Monte Carlo simulation method, including but not limited to distributed power generation output fluctuations, load changes, equipment failures, and external environmental impacts; In each simulation iteration, the system status is updated and the system response caused by each event is recorded, including the outage time, outage scope and recovery process; Calculate statistical indicators, including but not limited to average power outage duration and average power outage frequency, and evaluate the impact of distributed generation access on system reliability.

[0013] On the other hand, the present invention also provides a fault analysis system for accessing a distributed power supply to a distribution network, comprising: Establish a simulation model module to build an AC / DC hybrid distribution network model containing distributed power sources on the simulation software; Fault feature analysis module, used to analyze the changes in distribution network fault features after the distributed generation is connected, including changes in fault type, fault impact range, and fault current features; A fault injection and simulation module, used for injecting different types of faults into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and recording responses under various fault conditions; A fault signal extraction module, used to extract parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in the fault current; Protection strategy verification, used to verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model; The performance evaluation module evaluates the reliability of fault identification and protection action after the access of distributed power sources based on the generalized S transform and Pearson correlation coefficient, and uses the sequential Monte Carlo simulation method to analyze the impact of the access of distributed power sources on the system power outage time and frequency; Among them, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, including: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

[0014] The fault analysis method and system for the access of distributed power sources to the distribution network provided by the present invention, by establishing an AC / DC hybrid distribution network model containing distributed power sources, can comprehensively analyze the changes in fault characteristics of the distribution network after the access of distributed power sources, including fault type, impact range and current characteristics, and can effectively identify complex fault types such as short circuit, ground fault and island effect, providing a more accurate basis for fault diagnosis. Through fault injection and simulation, the protection strategy is verified and improved so that it can adapt to the complex working conditions after the access of distributed power sources. The adaptive protection strategy can automatically adjust the protection setting according to the access location, capacity and operating status of the distributed power sources, thereby improving the sensitivity and selectivity of the protection device. Based on performance evaluation, the impact of the access of distributed power sources on the stability of the distribution network can be effectively evaluated, which is conducive to improving the overall reliability and stability of the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 It is a flow chart of a fault analysis method for accessing a distributed power supply to a distribution network provided by an embodiment of the present invention; Figure 2 It is a structural diagram of a fault analysis system for accessing a distributed power supply to a distribution network provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Figure 1 The present invention provides a flow chart of a method for analyzing a fault of a distributed power source connected to a distribution network. The method can be executed by a computer, a tablet computer, or other devices.

[0019] See also Figure 1 The fault analysis method for distributed power supply access to the distribution network may include the following steps.

[0020] Step 101, establishing a simulation model: constructing an AC / DC hybrid distribution network model including distributed power sources on the simulation software.

[0021] In this step, the AC / DC hybrid distribution network model may include an AC bus, a transformer, a feeder, a distributed power model, and a load model. The distributed power model may establish corresponding inverter and power generation equipment models according to the type of distributed power, and the load model may include loads of different types of load characteristics. The simulation software may include Matlab / Simulink, PSCAD / EMTDC, and DIgSILENT PowerFactory. The AC bus is the core part of the distribution network, which is used to connect transformers, feeders, and distributed power sources. It can be modeled by defining parameters such as the voltage level and short-circuit capacity of the bus. For example, in Matlab / Simulink, the "AC Bus" module can be used to set the voltage and frequency of the bus. The transformer is used to realize the conversion between different voltage levels. It is necessary to set the rated capacity, transformation ratio, short-circuit impedance and other parameters of the transformer. For example, in PSCAD / EMTDC, the "Transformer" module can be used to model. The feeder is a line connecting the bus and the load. Its modeling needs to consider the resistance, reactance and capacitance parameters of the line. The modeling can be completed by defining parameters such as the length of the line and the wire model. For example, in DIgSILENT PowerFactory, the electrical parameters of a feeder can be set using the "Line" module.

[0022] Distributed Generation (DG) refers to small-scale power generation equipment distributed in the distribution network. Common types include photovoltaic power generation, wind power generation and energy storage systems. When modeling in simulation software, it is necessary to select the appropriate module according to the type of distributed generation and set the corresponding parameters.

[0023] Photovoltaic power generation system is a device that uses solar panels to convert solar energy into electrical energy. When modeling in simulation software, the following parameters are usually set, such as photovoltaic panel area, light intensity, temperature, conversion efficiency, maximum output power, etc. Wind power generation system is a device that uses wind to drive the wind wheel to rotate and convert mechanical energy into electrical energy through the generator. When modeling in simulation software, the following parameters need to be set, such as wind speed, rated power, cut-in wind speed, cut-out wind speed, rated wind speed, wind wheel diameter, etc. Load models can include characteristics of different types of loads, such as constant impedance load, constant power load and induction motor load. Constant impedance load can be modeled by setting the resistance and reactance of the load. Constant power load can set the active and reactive power of the load. Induction motor load can set the parameters of the motor, which can include stator resistance, stator leakage reactance, rotor resistance, rotor leakage reactance, excitation reactance, mechanical inertia time constant, rated power, rated voltage, power factor and induction motor load ratio. Energy storage systems (such as battery energy storage) are used to store and release electrical energy to balance the intermittency of distributed power sources and changes in load. When modeling in simulation software, the following parameters need to be set, such as energy storage capacity, charge and discharge power, charge and discharge efficiency, initial state of charge, self-discharge rate, etc.

[0024] Step 102, fault characteristic analysis: analyzing the changes in the fault characteristics of the distribution network after the distributed generation is connected, including the changes in the fault type, the fault impact range, and the fault current characteristics.

[0025] In this step, the changes in fault types include the manifestation of short-circuit faults on the DC side, abnormal voltage changes on the DC side due to ground faults, and the differences in islanding effects between the AC system and the DC side; the fault impact range includes the bidirectional impact and dynamic response characteristics caused by the access of distributed power sources; and the fault current characteristics include non-periodic components and amplitude fluctuations.

[0026] Step 103, fault injection and simulation: different types of faults are injected into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and responses under various fault conditions are recorded.

[0027] Step 104, fault signal extraction: extracting parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in the fault current.

[0028] Step 105: Verify the protection strategy: verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model.

[0029] Step 106, performance evaluation: Based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the access of distributed generation is evaluated, and the impact of the access of distributed generation on the system power outage time and frequency is analyzed by using the sequential Monte Carlo simulation method.

[0030] In this step, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, which may include: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

[0031] For example, in a distribution network containing distributed power sources, when a fault occurs, the characteristic quantities of the fault signal (such as frequency, amplitude and phase information) are extracted through generalized S transform. Assume that after the fault signal is preprocessed, its characteristic quantities are calculated with the preset short-circuit fault mode for the Pearson correlation coefficient. Preset threshold: The Pearson correlation coefficient threshold of the short-circuit fault mode is set to 0.8. Calculation result: The actual calculated Pearson correlation coefficient is 0.85. Judgment result: According to the correlation coefficient being higher than the threshold, it is judged to be a short-circuit fault, and the fault location is consistent with the preset mode. Protection action verification: By simulating the action logic of the longitudinal protection, verify that its action time is consistent with the preset value, thereby confirming the effectiveness of the protection strategy.

[0032] In this embodiment, by establishing an AC / DC hybrid distribution network model containing distributed power sources, the fault characteristic changes of the distribution network after the distributed power sources are connected can be comprehensively analyzed, including the fault type, impact range and current characteristics, and complex fault types such as short circuit, ground fault and island effect can be effectively identified, providing a more accurate basis for fault diagnosis. Through fault injection and simulation, the existing protection strategy is verified and improved to adapt to the complex working conditions after the distributed power sources are connected. The adaptive protection strategy can automatically adjust the protection setting according to the access location, capacity and operating status of the distributed power sources, and improve the sensitivity and selectivity of the protection device. Based on performance evaluation, the impact of the access of distributed power sources on the stability of the distribution network can be effectively evaluated, which is conducive to improving the overall reliability and stability of the distribution network.

[0033] In an embodiment of the present specification, for step 102, the fault feature analysis may include at least one of the following situations.

[0034] The first type: short-circuit fault analysis may include identifying the manifestation of short-circuit fault on the DC side, which may include but is not limited to the short-circuit fault characteristics between photovoltaic inverters or energy storage devices, and analyzing the differences between short-circuit faults and AC system short-circuit faults.

[0035] For example, in an AC / DC hybrid distribution network, assume that a short circuit occurs between the photovoltaic inverter and the energy storage device. A short circuit fault in an AC system is usually manifested as a sharp increase in current, while a short circuit fault on the DC side may be manifested as a rapid increase in current, but limited by the inverter control strategy, the current growth rate is slower than that of the AC system. Difference analysis: The short circuit fault current of the AC system is mainly determined by the system impedance, while the short circuit fault current on the DC side is also affected by the current limiting protection and control strategy of the inverter.

[0036] The second type: The analysis of ground faults may include analyzing the characteristics of ground faults on the DC side as increased or decreased voltage to ground, and the impact of voltage changes on the system.

[0037] For example, when a ground fault occurs on the DC side, assume that the system voltage to ground increases or decreases from the normal value, such as from ±100 V to ±120 V or ±80 V. Impact analysis: This voltage change may cause malfunction of other devices on the DC bus, such as overloading of the DC motor due to excessively high voltage, or failure to start normally due to too low voltage.

[0038] The third type: The analysis of the islanding effect may include simulating the action behavior of the distributed generation when the main grid fails, evaluating the effectiveness of the islanding detection and protection strategy, analyzing the impact of the islanding state on the AC system and the DC side, and the protection measures taken to avoid the islanding effect.

[0039] For example, suppose that in a photovoltaic power generation system, multiple rooftop photovoltaic devices are connected to the city grid through inverters. When a short power outage occurs in the grid, causing the inverter to be separated from the grid, the system enters an island state. In the island state, the voltage, frequency, and power balance of the AC system and the DC side are affected. For example, when the island effect occurs, the voltage on the AC side may fluctuate due to the loss of grid support, while the voltage on the DC side may rise or fall due to the dynamic response of the distributed power source. This state may cause equipment malfunction or damage. For example, the increase in DC bus voltage may cause the energy storage system to overcharge.

[0040] In order to prevent the risks brought by the islanding effect, the following protection measures can be taken, such as rapid shutdown: after detecting the islanding effect, the system automatically triggers the protection mechanism to isolate the inverter from the grid and shut down; reactive power disturbance method: by controlling the inverter or active power filter (APF) to inject reactive power disturbance, the reactive power balance of the island is broken, so as to quickly detect the islanding state; optimization control strategy: in the islanding state, the inverter can maintain the stability of voltage and frequency by dynamically adjusting the output power, thereby reducing the impact on the system.

[0041] The fourth type: In the analysis of the fault impact range, the two-way impact analysis may include analyzing the phenomenon that the fault impact range spans both the AC and DC systems after the distributed power supply is connected, analyzing the impact of this phenomenon on the fault location time, and measures to reduce the fault location time.

[0042] For example, assuming that after the distributed power source is connected, the AC side fault propagates to the DC side through the inverter, causing the DC side voltage to fluctuate. At the same time, the DC side fault may also reversely affect the AC system. Fault location time analysis: This bidirectional impact may increase the fault location time. Improvement measures: The fault location time can be shortened by optimizing the fault location algorithm or increasing the number of fault indicators.

[0043] Fifth: Dynamic response analysis may include analyzing the impact of the response characteristics of the distributed power grid-connected inverter on the fault development process and recovery speed, and analyzing the relationship between the dynamic adjustment of the inverter and the amplitude and phase of the fault current.

[0044] For example, the dynamic adjustment characteristics of the distributed power grid-connected inverter when a fault occurs are analyzed. It is assumed that after a short-circuit fault occurs on the AC side, the inverter limits the fault current by adjusting the output current phase and amplitude, thereby affecting the action time of the protection device.

[0045] Specifically, changes in the magnitude of the fault current: When a fault occurs, the inverter's control strategy usually limits the magnitude of the fault current. For example, through current limiting protection and fast response control, the inverter can limit the fault current to a lower level. This means that the magnitude of the fault current may decrease instead of increasing sharply as in traditional systems. Changes in the action time of the protection device: Because the inverter can effectively limit the magnitude of the fault current, the current change detected by the protection device may not be as significant as in traditional systems, which may lead to an increase in the action time of the protection device because it takes longer to confirm the fault.

[0046] Changes in fault current phase: The inverter can optimize system performance by adjusting the phase of the output current when a fault occurs. For example, by changing the current phase, the inverter can reduce the impact of the fault current on the system. This phase adjustment may cause the phase of the fault current to change, but the specific direction of change (advance or lag) depends on the control strategy. Changes in the operating time of the protection device: Changes in the fault current phase may affect the sensitivity of the protection device. If the phase adjustment can effectively reduce the impact of the fault current, the operating time of the protection device may increase because more time is needed to determine the severity of the fault.

[0047] Sixth: Non-periodic component analysis may include analyzing the content and changes of harmonic components in fault current caused by the nonlinear characteristics of distributed power inverters, and analyzing the impact of different distributed power types on harmonic content.

[0048] For example, when a photovoltaic power station is connected to the grid, the inverter's phase-locked loop (PLL) is disturbed by the grid voltage harmonics, resulting in phase tracking errors, which in turn cause the inverter output current distortion. This distortion increases the harmonic content in the fault current, especially high-frequency harmonics (such as 3rd and 5th harmonics). Traditional overcurrent protection devices usually judge faults based on the amplitude of the fundamental current. When the harmonic content in the fault current increases, the protection device may not be able to accurately detect the actual amplitude of the fault current, resulting in reduced sensitivity and failure to act in time.

[0049] When the background harmonics of the power grid are high, the inverter interacts with the grid harmonics, which may cause harmonics of a specific frequency to be amplified. For example, when there is a 5th harmonic in the power grid, the output of the inverter may be superimposed on it, further increasing the content of the harmonic of that frequency. Impact: The protection device may misjudge these harmonics as fault signals, resulting in false operation. This false operation not only increases the power outage time, but may also cause equipment damage.

[0050] In a distribution network with multiple distributed power sources connected, when a fault occurs, the inverters of different distributed power sources may generate different harmonic characteristics. For example, a photovoltaic inverter may generate high-frequency harmonics, while an energy storage inverter may generate low-frequency harmonics. Impact: When determining the fault location, the protection device usually relies on the characteristic changes of current and voltage. When the harmonic components in the fault current are complex, the protection device may not be able to accurately distinguish the fault location, resulting in a loss of selectivity.

[0051] Seventh: Amplitude fluctuation analysis may include analyzing the characteristics of fault current amplitude fluctuation caused by the dynamic response characteristics of distributed power sources, analyzing the impact of such fluctuation on the action of protection devices and improvement measures.

[0052] The dynamic response characteristics of distributed power sources (such as photovoltaic inverters) can cause the amplitude of the fault current to fluctuate. This fluctuation may cause the protection device to misjudge the fault type, resulting in malfunction or refusal to operate. For example, in a distribution network, after the distributed power source is connected, the dynamic adjustment of the inverter when a fault occurs causes the amplitude of the fault current to fluctuate. If the amplitude of the fault current is lower than the setting value of the protection device during the fluctuation process, the protection device may not be able to detect the fault, resulting in reduced sensitivity. For example, in a distribution network, after the distributed power source is connected, the amplitude fluctuation of the fault current causes the short-circuit current detected by the downstream protection device to decrease, causing the protection device to refuse to operate.

[0053] Rapid fluctuations in the fault current amplitude may cause the protection device to misjudge the fault type. For example, when the fault current rises or falls rapidly in a short period of time, the protection device may misjudge that the fault has been cleared or the fault type has changed, resulting in malfunction. For example, in a distribution network containing distributed power sources, the rapid disconnection characteristics of the inverter when a fault occurs causes the fault current amplitude to fluctuate, causing the protection device to misjudge it as a reverse short-circuit current, resulting in malfunction. Fault current amplitude fluctuations may cause the action range of the protection device to expand or shrink. For example, when the fault current amplitude exceeds the setting value of the protection device during the fluctuation process, the protection device may act in advance and expand the power outage range. By controlling the access capacity of distributed power sources, optimizing the setting value of the protection device, and adopting an adaptive protection strategy, the impact of fault current amplitude fluctuations on the sensitivity and selectivity of the protection device can be effectively alleviated. These measures can significantly improve the safety and reliability of the distribution network and adapt to the complex operating environment after the access of distributed power sources.

[0054] In this embodiment, through the detailed analysis of short-circuit faults, ground faults and islanding effects on the DC side and AC system, the characteristic changes of distribution network faults after the access of distributed power sources can be more accurately identified and understood, providing a more comprehensive basis for fault diagnosis. The influence of bidirectional influence and dynamic characteristic response on fault location time is clarified, and measures to reduce fault location time are proposed, which helps to improve fault handling efficiency. By analyzing the dynamic response characteristics, non-periodic components and amplitude fluctuations of distributed power grid-connected inverters on fault currents and protection device actions, theoretical support is provided for improving protection strategies.

[0055] In an embodiment of the present specification, for step 103, fault injection and simulation may include at least one of the following situations.

[0056] The first one is to simulate the behavior of distributed power sources when failure occurs under different access modes and analyze its impact on system stability.

[0057] Specifically, the first case may include the following: Constructing an access model for distributed power sources, wherein the access modes of the access model may include but are not limited to direct access, access through a transformer, and access through a converter; A fault point is set in the AC / DC hybrid distribution network model, and short circuit fault, ground fault or islanding fault is injected into the AC side and DC side respectively; Analyze the impact of different access methods on system stability.

[0058] (1) An example of direct access is as follows: Fault type: AC side short circuit fault. Example: PV power source is directly connected to the distribution network feeder. Fault location: The connection point between the PV power source and the feeder. Impact: The fault current increases significantly, which may cause the upstream protection device to malfunction and expand the scope of the power outage.

[0059] Fault type: DC side short circuit fault. Example: The energy storage system is directly connected to the DC bus. Fault location: The connection point between the energy storage system and the DC bus. Impact: The current rises rapidly, which may trigger the inverter overcurrent protection and cut off the connection.

[0060] Fault type: AC side ground fault. Example: PV power source is directly connected to the distribution network feeder, and a single-phase ground fault occurs. Fault location: The connection point between the PV power source and the feeder. Impact: A ground fault will cause the voltage at the fault point to drop and the voltage of the non-fault phase to increase. The magnitude of the fault current depends on the system grounding method and the location of the fault point.

[0061] Fault type: DC side ground fault. Example: The energy storage system is directly connected to the DC bus, and a single-pole ground fault occurs. Fault location: The connection point between the energy storage system and the DC bus. Impact: A DC side ground fault will cause abnormal changes in the DC bus voltage. If the positive pole is grounded, the DC bus positive pole voltage will drop and the negative pole voltage will increase; if the negative pole is grounded, the situation is the opposite.

[0062] Fault type: AC side islanding fault. Example: The PV power source is directly connected to the distribution network feeder, resulting in islanding. Fault location: The connection point between the PV power source and the feeder. Impact: Due to the loss of voltage and frequency support from the main grid, the voltage and frequency in the island area may fluctuate, causing equipment malfunction or damage.

[0063] Fault type: DC side islanding fault. Example: The energy storage system is directly connected to the DC bus, causing an islanding effect. Fault location: The connection point between the energy storage system and the DC bus. Impact: The islanding effect can cause fluctuations in the DC bus voltage and current, affecting the normal operation of the DC load.

[0064] (2) An example of access through a transformer is shown below: Fault type: AC side ground fault. Example: Wind turbine connected to the distribution network through a transformer. Fault location: Transformer low voltage side. Impact: Fault current distribution changes, protection selectivity decreases, and voltage sag may occur.

[0065] Fault type: DC side ground fault. Example: The energy storage system is connected to the DC side through a transformer. Fault location: The connection point between the high voltage side of the transformer and the DC bus. Impact: The DC side voltage changes abnormally, and the fault current propagates in the reverse direction to the AC side.

[0066] Fault type: AC side short circuit fault. Example: Wind turbines are connected to the distribution network through transformers. Fault location: transformer low voltage side. Impact: Short circuit faults can cause a sharp increase in the current at the fault point. The short circuit current on the transformer low voltage side may exceed the rated current of the transformer, or even its short circuit tolerance. This may cause the transformer protection device to operate, cut off the connection between the transformer and the distribution network, and expand the scope of the power outage.

[0067] Fault type: DC side short circuit fault. Example: The energy storage system is connected to the DC side through a transformer. Fault location: The connection point between the high voltage side of the transformer and the DC bus. Impact: A DC side short circuit fault will cause the current at the fault point to rise rapidly, which may exceed the short circuit tolerance of the transformer, causing the transformer protection device to operate and cut off the connection with the DC bus.

[0068] (3) An example of access via a converter is shown below: Fault type: AC side islanding fault. Example: The energy storage system is connected to the distribution network through a converter. Fault location: The connection point between the converter and the distribution network. Impact: In the islanding state, the impact current increases and the risk of malfunction of the protection device increases.

[0069] Fault type: DC side islanding fault. Example: The energy storage system is connected to the DC bus through the converter. Fault location: The connection point between the converter and the DC bus. Impact: DC side voltage and frequency fluctuations, and increased risk of malfunction of protection devices.

[0070] The second method is to inject transient faults of different intensities and durations into the AC / DC hybrid distribution network and analyze their impact on the dynamic response of the system and the action of the protection devices.

[0071] Specifically, the second situation may include: Select fault nodes in the AC / DC hybrid distribution network model and set transient faults of different intensities and durations; Inject transient faults into the AC side and DC side respectively; Analyze the impact of transient faults on system dynamic response and protection device operation.

[0072] (1) Specific examples of transient faults on the AC side are as follows. Fault type 1: short circuit fault. Intensity and duration: 1.5 times the rated current, duration 100ms. Fault location: midpoint of the AC feeder. Impact: The fault current rises rapidly, which may cause the protection device to operate for a longer time and the voltage to drop temporarily.

[0073] (2) Specific examples of transient faults on the DC side are shown below. Fault type 2: Ground fault. Intensity and duration: A ground current twice the rated current is injected into the DC bus for a duration of 50ms. Fault location: Somewhere on the DC bus. Impact: The current rises rapidly, which may trigger the converter station to lock out and the system to lose part of its power supply.

[0074] The third method is to simulate the behavior of distributed power sources when they fail under different environmental conditions and analyze their impact on the fault characteristics.

[0075] Specifically, the third situation may include: Setting environmental parameters of distributed power sources in the AC / DC hybrid distribution network model may include but is not limited to the light intensity of photovoltaic power sources, the wind speed of wind turbines, and the charging and discharging status of energy storage systems; Simulate the operating status of distributed power sources under different environmental parameters, inject faults into the AC and DC sides respectively and record the system response; Analyze the impact of environmental parameter changes on fault characteristics.

[0076] Specific examples and fault locations: (1) Changes in photovoltaic power environment: Fault type: AC side short circuit fault. Example: When the light intensity weakens (such as when the light intensity suddenly changes from 1000W / m² to 200W / m²), a short circuit fault is injected. Fault location: The connection point between the photovoltaic power source and the AC feeder. Impact: The fault current is reduced and the sensitivity of the protection device is reduced.

[0077] (2) Changes in the charging and discharging state of the energy storage system: Fault type: DC side islanding fault. Example: When the energy storage system switches from charging state to discharging state, an islanding fault is injected. Fault location: The connection point between the energy storage system and the DC bus. Impact: Increased inrush current, voltage drop, and reduced system stability.

[0078] (3) Wind speed change of wind turbine: Fault type: ground fault on the AC side. Example: When the wind speed weakens (e.g., when the wind speed suddenly changes from 8m / s to 2m / s), the output power of the wind turbine drops significantly, and a ground fault is injected at this time. Fault location: The connection point between the wind turbine and the AC feeder. Impact: The amplitude and phase of the fault current are unstable, the risk of malfunction of the protection device increases, and the system voltage drops temporarily.

[0079] Fault type: DC side ground fault. Example: When the wind speed weakens (for example, when the wind speed suddenly changes from 9m / s to 4m / s), the output power of the wind turbine decreases, and a ground fault is injected on the DC side. Fault location: The connection point where the wind turbine is connected to the DC bus through the converter. Impact: A DC side ground fault will cause abnormal changes in the DC bus voltage.

[0080] Fault type: DC side short circuit fault. Example: When the wind speed weakens (e.g., when the wind speed suddenly changes from 10m / s to 3m / s), the output power of the wind turbine fluctuates, and a short circuit fault is injected on the DC side. Fault location: The connection point where the wind turbine is connected to the DC bus through the converter. Impact: The fault current rises rapidly, but due to the decrease in the output power of the wind turbine, the current growth rate may be lower than normal, resulting in a longer action time for the protection device.

[0081] Fault type: three-phase short circuit fault on the AC side. Example: When the wind speed weakens (when the wind speed suddenly changes from 7m / s to 1m / s), the output power of the wind turbine drops significantly. At this time, a three-phase short circuit fault is injected on the AC side. Fault location: the connection point between the wind turbine and the AC feeder. Impact: The fault current amplitude decreases, the protection device may not be able to detect the fault in time, the sensitivity decreases, the voltage drops temporarily, and the system stability is affected.

[0082] The fourth method is to inject compound faults and analyze their impact on the system protection strategy.

[0083] Specifically, the fourth situation may include: Set up compound faults in the AC / DC hybrid distribution network model; Set different fault locations and fault occurrence sequences on the AC side and DC side to simulate compound fault scenarios; Analyze the impact of compound faults on protection strategies.

[0084] An example of a compound fault is shown below.

[0085] (1) Combination of AC side short circuit fault and ground fault: Fault type: AC side compound fault. Example: Short circuit fault and ground fault are injected simultaneously on the AC feeder. Fault location: Somewhere on the AC feeder. Impact: Fault current is complicated and the risk of protection device failure increases.

[0086] (2) Combination of DC side short circuit fault and islanding effect: Fault type: DC side compound fault. Example: Short circuit fault and islanding fault are injected into the DC bus at the same time. Fault location: Somewhere in the DC bus. Impact: Increased risk of malfunction of protection device and increased difficulty of fault isolation.

[0087] (3) Combination of single-phase ground fault and overload fault on the AC side: Fault type: AC side compound fault. Example: In the AC distribution network, a single-phase ground fault and an overload fault occur simultaneously. Fault location: A single-phase ground fault occurs at the branch end of an AC feeder; an overload fault occurs in the middle of another feeder. Impact: A single-phase ground fault causes the voltage at the fault point to drop, and the voltage of the non-fault phase to increase. The magnitude of the ground current depends on the system grounding method. An overload fault causes the feeder current to exceed the rated value, which may cause the protection device to malfunction.

[0088] (4) Combination of DC side ground fault and energy storage system overcharge fault: Fault type: DC side compound fault. Example: A DC side ground fault and an energy storage system overcharge fault occur simultaneously on the DC bus. Fault location: The ground fault occurs on the positive side of the DC bus; the energy storage system overcharge fault occurs inside the energy storage device connected to the DC bus. Impact: A DC side ground fault can cause abnormal changes in the DC bus voltage. Positive grounding can cause the positive voltage to drop and the negative voltage to increase. Overcharging of the energy storage system may trigger internal protection action, cutting off the connection between the energy storage system and the DC bus.

[0089] In this embodiment, by simulating the fault behavior of distributed power sources under different access modes, different environmental conditions and complex faults, the impact of faults on system stability, dynamic response and protection strategy is comprehensively analyzed, thereby providing data support and improvement direction for optimizing protection strategies and improving system reliability.

[0090] In an embodiment of the present specification, for step 104, fault signal extraction may include: Extract the maximum and minimum values ​​of fault current and fault voltage, etc. This information can reflect the intensity change of the fault signal.

[0091] The fault signal can also be converted from the time domain to the frequency domain by using a fast Fourier transform (FFT) to extract the frequency components in the fault signal, such as harmonic content, and of course, the fundamental wave.

[0092] In an embodiment of the present specification, verifying the effectiveness of the protection strategy in the AC / DC hybrid distribution network model may include: Verify the effectiveness of the protection strategy: In the AC / DC hybrid distribution network model, the effectiveness of protection strategies (such as overcurrent protection, distance protection, island detection protection, etc.) in fault identification, action time and selectivity is verified according to the changes in fault characteristics after the distributed power sources are connected.

[0093] The action behaviors of protection devices before and after the distributed generation are connected are compared through simulation data to evaluate their adaptability to changes in fault current, voltage and frequency.

[0094] Proposed improvement measures: Optimize the setting value of the protection device: According to the fault signal extraction results, readjust the setting value of the protection device to adapt to the fault current amplitude fluctuation and non-periodic components after the distributed power supply is connected.

[0095] Introducing adaptive protection strategies: Based on the dynamic changes of fault characteristics, adaptive protection strategies are adopted, such as directional protection elements and phase current difference fault components as protection action criteria, to improve the sensitivity and selectivity of protection devices.

[0096] Optimize inverter control strategy: Adjust the control strategy of distributed power inverters, such as low voltage ride-through capability, islanding effect detection and protection, to reduce the impact of faults on the system.

[0097] Verify the effectiveness of improvement measures: Under the improved protection strategy, fault injection and simulation are performed again to verify whether the action time, action range and fault isolation capability of the protection device meet the system requirements.

[0098] By comparing the simulation results before and after the improvement, the effectiveness of the protection strategy improvement measures is evaluated to ensure the reliability of the system after the distributed power source is connected.

[0099] In one embodiment of the present specification, calculating the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode may include: According to the preset fault mode library and historical simulation data, the correlation coefficient thresholds of different fault types and fault locations are set; For each fault characteristic quantity, calculate the Pearson correlation coefficient between it and the preset fault mode; Determine the fault type and location based on the threshold of the Pearson correlation coefficient and verify the accuracy of the action of the longitudinal protection after the distributed power source is connected, which may include: According to the comparison result of the correlation coefficient and the correlation coefficient threshold, the fault type and the fault location are determined; According to the determined fault type and fault location, simulate the action logic of the longitudinal protection to obtain the simulated action time and action range; The determined fault type, fault location, simulated action time and action range are compared with the preset fault type, fault location, action time and action range to verify the action accuracy of the longitudinal protection after the distributed power source is connected.

[0100] In this embodiment, for example, according to the preset fault mode library and historical simulation data, the thresholds of the Pearson correlation coefficient are set for different fault types (such as short circuit fault and ground fault). These thresholds are used for subsequent fault type and location judgment. For example, the correlation coefficient threshold of the short circuit fault is set to 0.8, and the correlation coefficient threshold of the ground fault is set to 0.75. Assuming that after the fault signal is transformed by the generalized S transform, the correlation coefficient calculation result of the extracted feature quantity and the short circuit fault mode is 0.82, and the correlation coefficient calculation result of the ground fault mode is 0.68. Since 0.82>0.8, it is judged as a short circuit fault. Since 0.68<0.75, the ground fault is excluded. The simulation results show that the action time of the longitudinal protection is 100ms, and the action range is consistent with the preset value. The determined fault type, fault location, simulated action time and action range are compared with the preset value to verify the action accuracy of the longitudinal protection after the distributed power supply is connected. For example, the preset short circuit fault action time is 100ms, and the actual simulation result is 100ms. The action range is consistent with the preset value, verifying that the protection action is accurate.

[0101] In an embodiment of the present specification, performing a generalized S transform on the fault signal to obtain a transformed fault feature quantity may include: Preprocess the fault signal; the preprocessing may include filtering and denoising. For example, suppose a fault occurs in a distribution network, and the collected fault signal contains high-frequency noise and low-frequency interference. Filter the signal through a digital filter (such as a low-pass filter or a band-pass filter) to remove high-frequency noise; at the same time, use methods such as wavelet transform to remove low-frequency interference and obtain a relatively pure fault signal.

[0102] Perform a generalized S transform on the preprocessed fault signal to decompose the fault signal into information in two dimensions: time and frequency, while retaining the amplitude and phase, and finally obtain the transformed fault feature quantity. For example, assume that the preprocessed fault signal is a time domain signal with a duration of 1 second and a sampling rate of 1000Hz. After performing a generalized S transform on the signal, a two-dimensional time-frequency matrix is ​​obtained, in which the horizontal axis represents time (0~1 second) and the vertical axis represents frequency (0~500Hz). The value of each point represents the signal amplitude and phase at that time and frequency.

[0103] Extract the fault feature quantity of the fault signal after the generalized S transform. For example, from the result of the generalized S transform, the extracted fault feature quantity may include the following. Amplitude feature: At the time of fault occurrence (such as 0.2 seconds), extract the amplitude change in a certain frequency range (such as around 50Hz). Frequency feature: Analyze the frequency distribution of the fault signal. For example, a short circuit fault may have a significant amplitude in a low frequency band (such as 50Hz), while a ground fault may be abnormal in a high frequency band (such as 100Hz). Phase feature: Extract the phase change of the fault signal. For example, a short circuit fault may cause a sudden phase change.

[0104] The specific example is as follows: Assume that a distribution network fails, and the collected fault signal includes the fault type, such as a three-phase short circuit fault, and the signal characteristics, such as the signal contains high-frequency noise and low-frequency interference.

[0105] The implementation process includes preprocessing: using a low-pass filter to remove high-frequency noise (such as components above 200Hz) and using wavelet transform to remove low-frequency interference (such as components below 10Hz).

[0106] The generalized S transform includes performing a generalized S transform on the preprocessed signal to obtain a time-frequency matrix. In the time-frequency matrix, it is observed that the amplitude of the 50 Hz frequency component increases significantly near the time when the fault occurs (e.g., 0.2 seconds).

[0107] Feature extraction includes extracting amplitude features: at 0.2 seconds, the amplitude of the 50Hz frequency increases from 10V in normal operation to 50V. Extracting frequency features: the fault signal is mainly concentrated around 50Hz, indicating a short circuit fault. Extracting phase features: the phase changes suddenly from 0 degrees to 180 degrees at the moment of the fault.

[0108] In this embodiment, the generalized S transform can accurately identify the fault type (short circuit fault) and fault characteristics (amplitude, frequency, phase change), providing a basis for subsequent fault location and protection strategy optimization.

[0109] In an embodiment of this specification, a sequential Monte Carlo simulation method is used to analyze the impact of the access of distributed power sources on the power outage time and frequency of the system, as shown below: Step 1: Initialize the system model and parameters, which may include but are not limited to the generation characteristics of distributed generation, load demand, grid structure and protection device settings.

[0110] For example, distributed power sources: photovoltaic power sources (capacity 100kW), wind turbines (capacity 50kW). Load demand: The total load is 200kW, distributed at different nodes. Grid structure: 10kV distribution network, including multiple feeders and branches. Protection device: Set the current protection device, and the action time is set to 0.1 second.

[0111] Step 2: Based on the preset failure modes and operating conditions, a series of random event sequences are generated using the sequential Monte Carlo simulation method. The events may include but are not limited to distributed power generation output fluctuations, load changes, equipment failures, and external environmental impacts.

[0112] For example, the randomly generated event sequence may include: the output of the photovoltaic power source suddenly changes from 100kW to 50kW due to changes in light intensity. The output of the wind turbine suddenly changes from 50kW to 30kW due to changes in wind speed. A short circuit fault occurs on a feeder line, which lasts for 0.1 seconds. The load demand increases by 20kW at a certain moment.

[0113] Step 3: In each simulation iteration, update the system status and record the system response caused by each event, which may include the power outage time, power outage scope and recovery process.

[0114] For example, in the first iteration: after the PV output suddenly changes, the system voltage drops by 5%. The wind turbine output decreases, and the system frequency drops by 0.1 Hz. The short-circuit fault causes the protection device to operate, and the power outage lasts for 0.1 seconds, covering 10 users downstream of the faulty feeder. The system restores power within 0.2 seconds.

[0115] Step 4: Calculate statistical indicators, including but not limited to average power outage time and average power outage frequency, to evaluate the impact of distributed power access on system reliability.

[0116] For example, after 1,000 simulation iterations: the average power outage time is 0.12 seconds. The average power outage frequency is 1.5 times per year. After the distributed power generation is connected, the system reliability decreases slightly, but by optimizing the protection strategy, the average power outage time can be reduced to 0.1 seconds and the power outage frequency can be reduced to 1.2 times per year.

[0117] In this embodiment, the impact of distributed generation access on the power outage time and frequency of distribution network is systematically analyzed through the sequential Monte Carlo simulation method, so as to provide a scientific basis for optimizing the configuration of distributed generation and protection strategy to improve the reliability of distribution network.

[0118] In summary, those skilled in the art can fully understand the technical solution of the present invention, and there is no unclear content.

[0119] Based on the same general inventive concept, the present invention also protects a fault analysis system for a distributed power supply connected to a distribution network, such as Figure 2 As shown, Figure 2 The structure diagram of the fault analysis system for accessing a distributed power supply to a distribution network provided by an embodiment of the present invention is as follows. The fault analysis system for accessing a distributed power supply to a distribution network provided by the present invention is described below. The fault analysis system for accessing a distributed power supply to a distribution network described below and the fault analysis method for accessing a distributed power supply to a distribution network described above can be referred to each other.

[0120] The fault analysis system for distributed power supply access to the distribution network may include a simulation model establishment module 201, a fault feature analysis module 202, a fault injection and simulation module 203, a fault signal extraction module 204, a protection strategy verification module 205 and a performance evaluation module 206.

[0121] Establishing a simulation model module 201 for building an AC / DC hybrid distribution network model containing distributed power sources on the simulation software; The fault characteristic analysis module 202 is used to analyze the changes in the fault characteristics of the distribution network after the distributed power supply is connected, including the changes in the fault type, the fault impact range and the fault current characteristics; The fault injection and simulation module 203 is used to inject different types of faults into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and record responses under various fault conditions; The fault signal extraction module 204 is used to extract parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in the fault current; The protection strategy verification module 205 is used to verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model; The performance evaluation module 206 evaluates the reliability of fault identification and protection action after the access of distributed power sources based on the generalized S transform and the Pearson correlation coefficient, and uses the sequential Monte Carlo simulation method to analyze the impact of the access of distributed power sources on the system power outage time and frequency.

[0122] Among them, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, including: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

[0123] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing the faults of distributed power supply access to a distribution network, characterized in that: include: Establish a simulation model: Build an AC / DC hybrid distribution network model containing distributed power sources on the simulation software; Fault feature analysis: Analyze the changes in distribution network fault features after the distributed generation is connected, including changes in fault type, fault impact range, and fault current characteristics; Fault injection and simulation: different types of faults are injected into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and responses under various fault conditions are recorded; Fault signal extraction: Extract parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in fault current; Protection strategy verification: verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model; Performance evaluation: Based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the access of distributed generation is evaluated, and the impact of the access of distributed generation on the power outage time and frequency of the system is analyzed by using the sequential Monte Carlo simulation method; Among them, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, including: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

2. The method for analyzing the fault of a distributed power supply connected to a distribution network according to claim 1, characterized in that: The changes in fault types include the manifestation of short-circuit faults on the DC side, abnormal voltage changes on the DC side due to ground faults, and differences in islanding effects between the AC system and the DC side; the fault impact range includes the bidirectional impact and dynamic response characteristics caused by the access of distributed power sources; The fault current characteristics include non-periodic components and amplitude fluctuations, and the fault characteristic analysis includes: The analysis of short-circuit faults includes identifying the manifestations of short-circuit faults on the DC side, including but not limited to the characteristics of short-circuit faults between photovoltaic inverters or energy storage devices, and analyzing the differences between short-circuit faults and AC system short-circuit faults; The analysis of ground faults includes analyzing the characteristics of ground faults on the DC side as an increase or decrease in voltage to ground, and the impact of voltage changes on the system; The analysis of the islanding effect includes simulating the action behavior of the distributed generation when the main power grid fails, evaluating the effectiveness of the islanding detection and protection strategy, analyzing the impact of the islanding state on the AC system and the DC side, and the protection measures taken to avoid the islanding effect; In the fault impact range analysis, the bidirectional impact analysis includes analyzing the phenomenon that the fault impact range spans both the AC and DC systems after the distributed power supply is connected, analyzing the impact of this phenomenon on the fault location time, and measures to reduce the fault location time; Dynamic response analysis includes analyzing the impact of the response characteristics of the distributed power grid-connected inverter on the fault development process and recovery speed, and analyzing the relationship between the dynamic adjustment of the inverter and the amplitude and phase of the fault current; The non-periodic component analysis includes analyzing the content and changes of harmonic components in the fault current caused by the nonlinear characteristics of the distributed power inverter, and analyzing the impact of different distributed power types on the harmonic content; Amplitude fluctuation analysis includes analyzing the characteristics of fault current amplitude fluctuation caused by the dynamic response characteristics of distributed power sources, analyzing the impact of this fluctuation on the action of protection devices and improvement measures.

3. The fault analysis method for distributed power supply access to distribution network according to claim 1 is characterized in that: The fault injection and simulation include: Simulate the behavior of distributed power sources when they fail under different access modes and analyze their impact on system stability; Inject transient faults of different intensities and durations into AC / DC hybrid distribution networks and analyze their impact on the system dynamic response and protection device operation; Simulate the behavior of distributed power sources when they fail under different environmental conditions and analyze their impact on the fault characteristics; Inject compound faults and analyze their impact on the system protection strategy.

4. The method for analyzing the fault of a distributed power supply connected to a distribution network according to claim 3, characterized in that: The simulated behavior of the distributed power source when a fault occurs in different access modes includes: Constructing an access model for distributed power sources, wherein the access modes of the access model include but are not limited to direct access, access through a transformer, and access through a converter; A fault point is set in the AC / DC hybrid distribution network model, and short circuit fault, ground fault or islanding fault is injected into the AC side and DC side respectively; Analyze the impact of different access methods on system stability; The method of injecting transient faults of different intensities and durations into the AC / DC hybrid distribution network includes: Select fault nodes in the AC / DC hybrid distribution network model and set transient faults of different intensities and durations; Inject transient faults into the AC side and DC side respectively; Analyze the impact of transient faults on system dynamic response and protection device action; The simulated behavior of the distributed power supply when a fault occurs under different environmental conditions includes: Setting environmental parameters of distributed power sources in the AC / DC hybrid distribution network model, including but not limited to the light intensity of the photovoltaic power source, the wind speed of the wind turbine generator, and the charging and discharging status of the energy storage system; Simulate the operating status of distributed power sources under different environmental parameters, inject faults into the AC and DC sides respectively and record the system response; Analyze the impact of environmental parameter changes on fault characteristics; The injection of compound faults and analysis of their impact on the system protection strategy include: Set up compound faults in the AC / DC hybrid distribution network model; Set different fault locations and fault occurrence sequences on the AC side and DC side to simulate compound fault scenarios; Analyze the impact of compound faults on protection strategies.

5. The method for analyzing the fault of a distributed power supply connected to a distribution network according to claim 1, characterized in that: The calculating of the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode includes: According to the preset fault mode library and historical simulation data, the correlation coefficient thresholds of different fault types and fault locations are set; For each fault characteristic quantity, calculate the Pearson correlation coefficient between it and the preset fault mode; The method of judging the fault type and location according to the threshold of the Pearson correlation coefficient and verifying the accuracy of the action of the longitudinal protection after the distributed power source is connected includes: According to the comparison result of the correlation coefficient and the correlation coefficient threshold, the fault type and the fault location are determined; According to the determined fault type and fault location, simulate the action logic of the longitudinal protection to obtain the simulated action time and action range; The determined fault type, fault location, simulated action time and action range are compared with the preset fault type, fault location, action time and action range to verify the action accuracy of the longitudinal protection after the distributed power source is connected.

6. The method for analyzing the fault of a distributed power supply connected to a distribution network according to claim 1, characterized in that: The generalized S transform is performed on the fault signal to obtain the transformed fault feature quantity, including: Preprocessing the fault signal; wherein the preprocessing includes filtering and denoising; The preprocessed fault signal is subjected to generalized S transform to decompose the fault signal into information in two dimensions, time and frequency, while retaining the amplitude and phase to obtain the transformed fault feature quantity.

7. The method for analyzing the fault of a distributed power supply connected to a distribution network according to claim 1, characterized in that: The sequential Monte Carlo simulation method is used to analyze the impact of the access of distributed generation on the power outage time and frequency of the system, including: Initialize system models and parameters, including but not limited to distributed generation characteristics, load demand, grid structure, and protection device settings; Based on the preset failure modes and operating conditions, a series of random event sequences are generated using the sequential Monte Carlo simulation method, including but not limited to distributed power generation output fluctuations, load changes, equipment failures, and external environmental impacts; In each simulation iteration, the system status is updated and the system response caused by each event is recorded, including the outage time, outage scope and recovery process; Calculate statistical indicators, including but not limited to average power outage time and average power outage frequency, and evaluate the impact of distributed power generation access on system reliability.

8. A fault analysis system for distributed power supply access to a distribution network, characterized in that: include: Establish a simulation model module to build an AC / DC hybrid distribution network model containing distributed power sources on the simulation software; Fault feature analysis module, used to analyze the changes in fault features of the distribution network after the distributed generation is connected, including changes in fault type, fault impact range, and fault current features; A fault injection and simulation module, used for injecting different types of faults into the AC / DC hybrid distribution network model, including short circuit faults and ground faults on the AC side and short circuit faults, ground faults and islanding faults on the DC side, and recording responses under various fault conditions; A fault signal extraction module, used to extract parameters through simulation data, including but not limited to fault current, voltage, frequency and harmonic components in the fault current; A protection strategy verification module, used to verify the effectiveness of the protection strategy in the AC / DC hybrid distribution network model; The performance evaluation module evaluates the reliability of fault identification and protection action after the access of distributed power sources based on the generalized S transform and Pearson correlation coefficient, and uses the sequential Monte Carlo simulation method to analyze the impact of the access of distributed power sources on the system power outage time and frequency; Among them, based on the generalized S transform and Pearson correlation coefficient, the reliability of fault identification and protection action after the distributed generation is connected is evaluated, including: Perform generalized S transformation on the fault signal to obtain the transformed fault feature quantity; Calculate the Pearson correlation coefficient between the fault characteristic quantity and the preset fault mode; The fault type and location are determined based on the threshold of the Pearson correlation coefficient, and the accuracy of the longitudinal protection after the distributed power source is connected is verified.

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