Relay protection method, device and system for microgrid

Abstract

The application provides a kind of micro-grid relay protection method, device and system, it is related to micro-grid technical field.The method comprises: collecting the electrical quantity and operating state of micro-grid public coupling point;Using hybrid island detection method based on electrical quantity and operating state carries out island detection, determines the mode recognition result of micro-grid;Hybrid island detection method is constructed based on passive detection method and active detection method;Mode recognition result is one of grid-connected mode, off-grid mode and switching transient mode;Determine the target relay protection strategy corresponding to mode recognition result based on set mapping strategy;Set mapping strategy includes the relay protection strategy corresponding to grid-connected mode, off-grid mode and switching transient mode respectively.The application is used to solve the problem of the lack of switching transient protection logic in the existing micro-grid dual-mode operation mode.

Description

Technical Field

[0001] This invention relates to the field of microgrid technology, and more specifically to a relay protection method, a relay protection device, a relay protection system, a machine-readable storage medium, and a computer program product for microgrids. Background Technology

[0002] As a core carrier for the efficient utilization of distributed power sources, microgrids possess dual-mode operation capabilities, including grid-connected and off-grid operation. Their core function is to operate in grid-connected mode when the main grid is functioning normally, enabling renewable energy to be fed into the grid; and to quickly switch to off-grid mode during main grid failures or maintenance to ensure continuous power supply to critical loads, before smoothly reconnecting to the main grid once it is restored. Currently, separate-mode relay protection schemes and islanding detection technologies exist for the dual-mode operation of microgrids.

[0003] Different modes of relay protection scheme: Different protection settings and action criteria are designed for the two operating modes of microgrids: grid-connected and off-grid. In grid-connected mode, relying on the large short-circuit current provided by the main grid, traditional directional overcurrent protection and undervoltage protection are used as the main and backup protections, respectively, and the operating current is set according to the maximum short-circuit current under grid-connected conditions. In off-grid mode, the fault current is only provided by the inverter-type distributed power source and is subject to the current limiting control of the inverter. The fault current amplitude is only 1.2 to 2 times the rated current. Therefore, low-amplitude overcurrent protection is used as the main protection, and some schemes will be combined with voltage criteria to assist in fault identification.

[0004] Islanding detection technology is divided into two types: passive detection and active detection. Passive detection monitors electrical quantities such as voltage amplitude, frequency, and phase at the point of common coupling (PCC) in real time. When these electrical quantities exceed a preset threshold, a main grid fault is identified, triggering off-grid switching. Active detection injects small disturbances (such as frequency shifts or voltage disturbances) into the microgrid and determines whether it is in an islanded state based on the disturbance response characteristics, thus solving the problem of missed detection by passive detection under light load conditions.

[0005] However, the current microgrid dual-mode operation features incomplete mode-specific relay protection, lacking transitional protection logic. Specifically, existing technology only distinguishes between grid-connected and off-grid stable operating modes, failing to treat the transitional process between grid connection and off-grid (lasting 5-200ms) as an independent operating state. During this transitional period, voltage and frequency fluctuate drastically, and current amplitude and direction change rapidly. Traditional protection logic does not adjust synchronously, easily leading to protection maloperation (e.g., inrush current triggering protection tripping during grid-connected to off-grid transition) or failure to operate (e.g., fault current not reaching the set value during off-grid to grid-connected transition).

[0006] It should be noted that the information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a relay protection method, device, and system for microgrids to solve the problem of lack of switching transient protection logic for the sub-mode relays in the existing dual-mode operation of microgrids.

[0008] To achieve the above objectives, embodiments of the present invention provide a relay protection method for a microgrid, comprising: Collect electrical quantities and operating status at the common coupling point of the microgrid; A hybrid islanding detection method is used to perform islanding detection based on the electrical quantities and the operating status to determine the pattern recognition result of the microgrid; the hybrid islanding detection method is constructed based on passive detection method and active detection method; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode; The target relay protection strategy corresponding to the pattern recognition result is determined based on the set mapping strategy; the set mapping strategy includes the relay protection strategies corresponding to grid-connected mode, off-grid mode and switching transient mode respectively.

[0009] Optionally, the method of using a hybrid islanding detection approach to perform islanding detection based on the electrical quantities and the operating status, and to determine the pattern recognition result of the microgrid, includes: A preliminary detection method is used to perform initial detection based on the electrical quantities and operating status to obtain preliminary detection results; If the preliminary detection results indicate that the switch at the common coupling point is closed and the electrical quantity is not within the preset threshold range, the microgrid is subjected to multiple islanding detections using an active detection method to obtain multiple islanding detection results. Based on the matching results of the multiple islanding detections and the comprehensive mode conditions, the mode recognition result of the microgrid is determined; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

[0010] Optionally, determining the microgrid pattern recognition result based on the matching result of the multiple island detection results and the comprehensive pattern conditions includes: If the results of the multiple islanding detections all match the mode conditions of the grid-connected mode, the mode recognition result of the microgrid is determined to be the grid-connected mode. If the results of the multiple island detections all match the mode conditions of the off-grid mode, the mode recognition result of the microgrid is determined to be off-grid mode. If the results of the multiple island detections all match the mode conditions of the switching transient mode, the mode recognition result of the microgrid is determined to be the switching transient mode.

[0011] Optionally, determining the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy includes: When the pattern recognition result is a grid-connected mode, the target relay protection strategy corresponding to the grid-connected mode is determined to be to call the grid-connected protection setting library, use directional inverse time overcurrent protection as the main protection, and use undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current of the grid connection, and the direction criterion is that the fault current direction points to the line. When the pattern recognition result is an off-grid mode, the target relay protection strategy corresponding to the off-grid mode is determined to be to call the off-grid protection setting library, adopt amplitude inverse time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, cancel the direction criterion, and set the operating current according to the set multiple range of the rated current of the distributed power source. If the pattern recognition result is a switching transient mode, the target relay protection strategy corresponding to the switching transient mode is determined to be to call the switching transient setting library, block the main protection, and only activate the overcurrent instantaneous trip protection and overvoltage protection or the overcurrent instantaneous trip protection and undervoltage protection.

[0012] Optionally, after determining the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy, the method further includes: In the event of a fault in the main network, a trip command is sent to the fault isolation layer to drive the corresponding switch to trip. If the fault is not cleared, the switch corresponding to the fault is controlled to remain in the tripped state. If the fault clearance status is cleared, the process jumps to the step of using a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating status, and determining the microgrid pattern recognition result, and then re-executes the pattern recognition and relay protection strategy determination.

[0013] Optionally, the method further includes: In the event of grid-connected / off-grid switching, coordinate the opening and closing actions of the common coupling point switch, the control mode switching of distributed power sources, and the switching of the target relay protection strategy corresponding to the microgrid.

[0014] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using the hybrid islanding detection method, a common coupling point trip command is sent to the common coupling point switch, and the target relay protection strategy corresponding to the microgrid is switched to the relay protection strategy corresponding to the transient mode. Switch the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode. After the first set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the off-grid mode.

[0015] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When the electrical quantity of the main grid is detected to meet the set grid connection requirements, the distributed power source is controlled to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within the set error range. Send a common coupling point closing command to the common coupling point switch, and at the instant the common coupling point switch closes, switch the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode; Switch the control mode of the distributed power source from constant voltage and constant frequency control mode to constant power control mode; After the second set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the grid-connected mode.

[0016] On the other hand, embodiments of the present invention also provide a relay protection device for a microgrid, comprising: The data acquisition module is used to collect electrical quantities and operating status at the common coupling point of the microgrid; The detection module is used to perform islanding detection based on the electrical quantities and the operating status using a hybrid islanding detection method, and to determine the pattern recognition result of the microgrid; the hybrid islanding detection method is constructed based on passive detection method and active detection method; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode; The determination module is used to determine the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy; the set mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode and switching transient mode respectively.

[0017] Optionally, the method of using a hybrid islanding detection approach to perform islanding detection based on the electrical quantities and the operating status, and to determine the pattern recognition result of the microgrid, includes: A preliminary detection method is used to perform initial detection based on the electrical quantities and operating status to obtain preliminary detection results; If the preliminary detection results indicate that the switch at the common coupling point is closed and the electrical quantity is not within the preset threshold range, the microgrid is subjected to multiple islanding detections using an active detection method to obtain multiple islanding detection results. Based on the matching results of the multiple islanding detections and the comprehensive mode conditions, the mode recognition result of the microgrid is determined; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

[0018] Optionally, determining the microgrid pattern recognition result based on the matching result of the multiple island detection results and the comprehensive pattern conditions includes: If the results of the multiple islanding detections all match the mode conditions of the grid-connected mode, the mode recognition result of the microgrid is determined to be the grid-connected mode. If the results of the multiple island detections all match the mode conditions of the off-grid mode, the mode recognition result of the microgrid is determined to be off-grid mode. If the results of the multiple island detections all match the mode conditions of the switching transient mode, the mode recognition result of the microgrid is determined to be the switching transient mode.

[0019] Optionally, determining the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy includes: When the pattern recognition result is a grid-connected mode, the target relay protection strategy corresponding to the grid-connected mode is determined to be to call the grid-connected protection setting library, use directional inverse time overcurrent protection as the main protection, and use undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current of the grid connection, and the direction criterion is that the fault current direction points to the line. When the pattern recognition result is an off-grid mode, the target relay protection strategy corresponding to the off-grid mode is determined to be to call the off-grid protection setting library, adopt amplitude inverse time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, cancel the direction criterion, and set the operating current according to the set multiple range of the rated current of the distributed power source. If the pattern recognition result is a switching transient mode, the target relay protection strategy corresponding to the switching transient mode is determined to be to call the switching transient setting library, block the main protection, and only activate the overcurrent instantaneous trip protection and overvoltage protection or the overcurrent instantaneous trip protection and undervoltage protection.

[0020] Optionally, the device further includes: The first control module is used to send a trip command to the fault isolation layer to drive the switch corresponding to the fault to trip when there is a fault in the main grid; when the fault clearance status is not cleared, it controls the switch corresponding to the fault to remain in the tripped state; when the fault clearance status is cleared, it jumps to the step of using the hybrid islanding detection method to perform islanding detection based on the electrical quantity and the operating status to determine the pattern recognition result of the microgrid and re-executes the pattern recognition and relay protection strategy determination.

[0021] Optionally, the device further includes: The coordination module is used to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid in the event of grid-to-off-grid switching.

[0022] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using the hybrid islanding detection method, a common coupling point trip command is sent to the common coupling point switch, and the target relay protection strategy corresponding to the microgrid is switched to the relay protection strategy corresponding to the transient mode. Switch the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode. After the first set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the off-grid mode.

[0023] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When the electrical quantity of the main grid is detected to meet the set grid connection requirements, the distributed power source is controlled to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within the set error range. Send a common coupling point closing command to the common coupling point switch, and at the instant the common coupling point switch closes, switch the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode; Switch the control mode of the distributed power source from constant voltage and constant frequency control mode to constant power control mode; After the second set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the grid-connected mode.

[0024] On the other hand, the present invention also provides a relay protection system for a microgrid, comprising: The operation mode perception layer is used to collect electrical quantities and operating status at the common coupling point of the microgrid; a hybrid islanding detection method is used to perform islanding detection based on the electrical quantities and operating status to determine the microgrid's mode recognition result; the hybrid islanding detection method is constructed based on passive detection method and active detection method; the mode recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode; An adaptive protection decision layer is used to determine the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy; the set mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode and switching transient mode respectively.

[0025] Optionally, the system further includes: The collaborative control layer is used to receive control signals from the operation mode perception layer or the adaptive protection decision layer in the event of a grid-connected / off-grid switchover, so as to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid.

[0026] On the other hand, the present invention also provides a machine-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described relay protection method for microgrids.

[0027] On the other hand, the present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the above-mentioned relay protection method for microgrids.

[0028] Through the above technical solution, this embodiment of the invention utilizes a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating state, determine the microgrid's pattern recognition result, and then determine the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy. The set mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively. Thus, this embodiment of the invention clearly divides the microgrid's operating state into three operating modes—grid-connected, off-grid, and switching transient (0~200ms)—through hybrid islanding detection, rather than the traditional binary mode, providing a foundation for mode-specific protection. Furthermore, this embodiment of the invention designs independent relay protection strategies for each of the three operating modes, solving the problems of false tripping in grid-connected mode, failure to trip in off-grid mode, and instability in switching transient mode. Therefore, this embodiment of the invention solves the problem of the lack of switching transient protection logic in the mode-specific relays of existing microgrid dual-mode operation.

[0029] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0030] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic flowchart of the relay protection method for microgrids provided by the present invention; Figure 2This is a schematic diagram of the structure of the relay protection device for microgrids provided by the present invention; Figure 3 This is a schematic diagram of the relay protection system for a microgrid provided by the present invention. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0032] First, the technical terms involved in this invention will be explained: (1) PCC: Point of Common Coupling, refers to the interface node connecting the microgrid and the main grid, including the PCC switch, which is the core component for grid-connected and off-grid switching; (2) DG: Distributed Generation, refers to small power equipment such as photovoltaic, energy storage, and wind power connected to a microgrid; (3) PQ control: constant power control, the common control mode of DG under grid connection mode, to maintain stable output power; (4) V / f control: constant voltage and constant frequency control, the common control mode of DG in off-grid mode, to maintain the stability of microgrid voltage and frequency.

[0033] Although existing technologies can achieve grid-connected and off-grid switching and basic protection for microgrids, they lack sufficient protection coordination during the transient process of grid-connected and off-grid switching, and cannot solve the problems of protection maloperation, failure to operate, and fault escalation throughout the entire operation cycle of microgrids. The specific shortcomings are as follows: 1. Incomplete division of operating modes and lack of transient protection logic: Existing technology only classifies two stable operating modes: grid-connected and off-grid, without treating the transient process of grid-connected to off-grid switching (duration 5~200ms) as an independent operating state. During the switching transient, voltage and frequency fluctuate drastically, and current amplitude and direction change rapidly. Traditional protection logic does not adjust synchronously, which easily leads to protection maloperation (such as protection tripping triggered by inrush current when switching from grid-connected to off-grid) or failure to operate (such as the fault current not reaching the set value when switching from off-grid to grid-connected).

[0034] 2. Asynchronous protection settings and switching processes, resulting in poor adaptability: Existing protection setting switching relies on delayed feedback from pattern recognition, failing to coordinate with PCC switch operation and distributed power supply control mode switching in a timely manner. For example, when switching from grid-connected to off-grid, after the PCC switch opens, the protection settings remain at the high setting of the grid-connected mode, causing small current faults in the off-grid mode to fail to trigger protection action (failure to operate); when switching from off-grid to grid-connected, after the PCC switch closes, the protection settings do not switch to the grid-connected mode in a timely manner, leading to inrush current triggering protection maloperation.

[0035] 3. Disconnect between islanding detection and protection action: In existing technologies, islanding detection is only used to trigger the PCC switch action. The detection result is not directly linked to the protection logic adjustment, resulting in a delay in protection mode switching after islanding is detected. During the transient period, the fault cannot be handled in a timely manner, which can easily lead to the escalation of the fault. At the same time, some passive detection schemes have the problem of missing detection under light loads, and the disturbances injected by active detection schemes can easily affect power quality.

[0036] 4. Incomplete protection criteria in off-grid mode: In the existing technology, the off-grid mode only adopts low-amplitude overcurrent protection, without considering the bidirectional flow characteristics of power flow inside the microgrid, and still retains the directional criteria of the grid-connected mode, which makes it impossible to trigger protection action for some reverse faults; and lacks auxiliary criteria, making it impossible to effectively distinguish between fault current and normal load current, resulting in a high false alarm rate and missed alarm rate.

[0037] 5. Chaotic timing of switching process and protection action: The existing technology does not clearly define the blocking, switching and reset sequence of protection during the switching process, which leads to conflict between PCC switch action and protection trip action, resulting in problems such as over-level tripping and power outage in non-fault areas, and cannot guarantee uninterrupted power supply to important loads during the switching process.

[0038] In view of this, in order to solve at least one of the above-mentioned technical problems, embodiments of the present invention provide a relay protection method, device and system for microgrids.

[0039] Method Implementation Examples Please refer to Figure 1 This invention provides a relay protection method for a microgrid, comprising: Step 100: Collect electrical quantities and operating status of the microgrid's common coupling point.

[0040] In some embodiments, the relay protection method for microgrids according to the present invention can be implemented based on a relay protection system for microgrids. The relay protection system for microgrids consists of an operation mode perception layer, an adaptive protection decision layer, a collaborative control layer, a fault isolation layer, and a human-machine interface and backend unit. Each layer of modules works collaboratively to achieve adaptive protection throughout the entire process of microgrid grid-to-grid switching. The specific architecture is described as follows: Main grid and microgrid connection: The main grid is connected to the microgrid bus via a common coupling point (PCC, including the PCC switch). The PCC is the core interface for microgrid grid-to-grid switching; its closed state corresponds to grid-connected operation, and its open state corresponds to off-grid operation. Microgrid core unit: The microgrid bus connects distributed power generation units (including photovoltaic, energy storage, converters, etc.) and load units. Distributed power generation units can switch control modes (PQ control / V / f control) according to the operation mode. Load units include important loads and general loads, realizing the supply and consumption of electrical energy. The core of the operation mode perception layer is the mode perception unit, which includes electrical quantity acquisition modules (such as voltage acquisition modules, frequency acquisition modules, and phase acquisition modules), PCC switch status monitoring modules, and hybrid islanding detection modules. First, the operation mode perception layer controls the real-time acquisition of electrical quantities (such as voltage U, current I, frequency f, and phase θ) at the common coupling point and the microgrid bus, as well as the operating status of the common coupling point (open or closed). It should be noted that the operation mode perception layer can also filter and denoise the raw data of the electrical quantities at the common coupling point and the microgrid bus to ensure data accuracy.

[0041] Step 200: Utilize a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating status, and determine the microgrid's pattern recognition result; the hybrid islanding detection method is constructed based on passive detection and active detection methods; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode.

[0042] The control operation mode perception layer uses a hybrid islanding detection module to accurately identify the operation mode (grid-connected, off-grid, and switching transient) based on the electrical quantities and the operation status, and transmits the collected signals and mode identification signals to the adaptive protection decision layer. In some embodiments, the hybrid islanding detection method is used to perform islanding detection based on the electrical quantities and the operation status to determine the microgrid's mode recognition result, including: using a passive detection method to perform preliminary detection based on the electrical quantities and the operation status to obtain a preliminary detection result; when the preliminary detection result indicates that the switch of the common coupling point is closed and the electrical quantity is not within a preset threshold range, using an active detection method to perform islanding detection on the microgrid to obtain an islanding detection result; and determining the microgrid's mode recognition result based on the matching result of the islanding detection result and the comprehensive mode conditions.

[0043] The hybrid islanding detection module of the operation mode perception layer in this embodiment of the invention adopts a strategy of "passive detection as the main method and active detection as the auxiliary method" to analyze the raw data of electrical quantities at the preprocessed common coupling point and the microgrid bus. The passive detection method monitors whether the voltage, frequency, and phase at the common coupling point and the microgrid bus are within a preset threshold range, and combines this with the switch status of the common coupling point to preliminarily determine the operation mode. It should be noted that under normal circumstances, the common coupling point switch is closed, and the system operates in grid-connected mode, continuously monitoring whether the voltage, frequency, and phase at the common coupling point port are within the preset threshold range. 1. If the common coupling point switch is closed, and the voltage, frequency, and phase are all within the grid-connected steady-state threshold (preset threshold range), then the passive detection is valid, and the system is in grid-connected mode; active detection is not initiated. 2. If the common coupling point switch is open, the system is in off-grid mode, and active detection is blocked throughout. 3. If the common coupling point switch is closed, and any electrical quantity parameter of voltage, frequency, or phase is outside the preset threshold range, then the passive detection method is abnormal, and the active detection method is activated to verify the islanding status. Therefore, if the preliminary detection result of the passive detection method indicates that the switch at the common coupling point is closed, and the electrical quantity is not within the preset threshold range, for example, if the passive detection shows an abnormality (such as the voltage exceeding 0.85~1.15U), n If the islanding status is confirmed based on the disturbance response characteristics, the active detection method is activated. A high-frequency micro-disturbance of 200-500Hz is injected into the microgrid through distributed power sources. The detection time is ≤5ms. If the corresponding integrated mode conditions are met, the operating mode is locked, and a mode identification signal (or mode recognition result, including grid-connected / off-grid / switching transients) is output to the adaptive protection decision layer.

[0044] The comprehensive mode conditions include mode conditions for grid-connected mode, off-grid mode, and switching transient mode. In some embodiments, the mode conditions for grid-connected mode can be: grid-connected state: the common coupling point switch is closed, and when a high-frequency disturbance is injected, the high-frequency disturbance component of the system is quickly absorbed by the main grid, and electrical quantities such as voltage, frequency, and phase remain within the preset threshold range after a brief fluctuation and stabilization. When the islanding detection result matches the above-mentioned mode conditions for grid-connected mode, the microgrid's mode identification result is determined to be grid-connected mode. The mode conditions for off-grid mode can be: off-grid state: the common coupling point switch is open, and when a high-frequency disturbance is injected, the high-frequency disturbance component of the system cannot be quickly absorbed by the small power source alone, the waveform fluctuates significantly, and electrical quantity parameters such as voltage, frequency, and phase deviate from the preset threshold range. When the islanding detection result matches the above-mentioned mode conditions for off-grid mode, the microgrid's mode identification result is determined to be off-grid mode. The mode conditions for switching transient mode can be: the disturbance response continuously changes, and the waveform is unstable. When the islanding detection result matches the mode conditions for switching transient modes as described above, the microgrid's mode recognition result is determined to be off-grid mode.

[0045] Existing passive detection schemes sometimes miss detection under light loads, while disturbances injected by active detection schemes can easily affect power quality. This invention achieves rapid identification at the 5ms level through hybrid islanding detection, clearly dividing the microgrid operating state into three types: grid-connected, off-grid, and switching transient (0~200ms), rather than the traditional binary mode, thus providing a foundation for mode-specific protection.

[0046] Step 300: Determine the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy.

[0047] The adaptive protection decision layer determines the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy. The set mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively. The core of the adaptive protection decision layer is the adaptive protection decision unit, which includes a pattern recognition module, a grid-connected setting library, an off-grid setting library, a switching transient setting library, and a time-limit coordination module. The core function of this layer is to receive signals from the pattern perception layer, lock the current operating mode through the pattern recognition module, call protection settings and action criteria from the corresponding setting library, calculate the action time limit through the time-limit coordination module, generate a protection control signal, and transmit it to the collaborative control layer. In other words, the adaptive protection decision layer performs adaptive protection logic matching. The adaptive protection decision layer calls protection settings and action criteria from the corresponding setting library according to the pattern recognition result.

[0048] In one embodiment, determining the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy includes: when the pattern recognition result is a grid-connected mode, determining the target relay protection strategy corresponding to the grid-connected mode as calling the grid-connected protection setting library, using directional inverse-time overcurrent protection as the main protection, and undervoltage protection and over-frequency / under-frequency protection as backup protection, setting the operating current according to the maximum short-circuit current of the grid connection, and using the direction criterion as the fault current direction pointing to the line; when the pattern recognition result is an off-grid mode, determining the target relay protection strategy corresponding to the off-grid mode as calling the off-grid protection setting library, using amplitude inverse-time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, canceling the direction criterion, and setting the operating current according to the set multiple range of the rated current of the distributed power source; when the pattern recognition result is a switching transient mode, determining the target relay protection strategy corresponding to the switching transient mode as calling the switching transient setting library, blocking the main protection, and only activating overcurrent instantaneous trip protection and overvoltage protection or overcurrent instantaneous trip protection and undervoltage protection.

[0049] That is, when the pattern recognition result indicates a grid-connected mode, the adaptive protection decision layer calls the grid-connected protection setting library, adopting directional inverse-time overcurrent protection as the main protection, and undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current in the grid, and the direction criterion is that the fault current direction points towards the line. Among them, the directional inverse-time overcurrent protection is a protection that integrates a direction discrimination element on the basis of traditional inverse-time overcurrent protection. The directional inverse-time overcurrent protection stipulates that: the inverse-time timing logic is only activated when the fault current flows from the bus to the protected line (i.e., in the positive direction); if the current direction is opposite (flowing from the line to the bus), the protection is immediately blocked and does not operate.

[0050] When the pattern recognition result indicates off-grid mode, the adaptive protection decision layer calls the off-grid protection setting library, adopting low-amplitude inverse-time overcurrent protection (i.e., amplitude inverse-time overcurrent protection) + voltage drop auxiliary criterion as the main protection, canceling the direction criterion (to adapt to bidirectional power flow), and setting the operating current to 1.2 to 1.5 times the rated current of the distributed power source. Low-amplitude inverse-time overcurrent protection is a type of inverse-time overcurrent protection specifically designed for islanded operation mode. Its core feature is a significant reduction in the current initiation value (Ip), usually combined with an adjustment of the time constant (K), forming a steeper or left-shifted operating curve, enabling it to respond sensitively and quickly to very low-amplitude short-circuit currents in islanded mode. The voltage drop auxiliary criterion refers to continuously monitoring the voltage at the point of connection (PCC). When a voltage drop exceeding a preset large threshold (e.g., dropping to 85% or below the rated voltage) is detected within a very short time (usually within 1-2 cycles), a highly reliable "grid anomaly" signal is immediately issued. Existing technologies only employ low-amplitude overcurrent protection in off-grid mode, failing to consider the bidirectional power flow characteristics within the microgrid and retaining the directional criteria of the grid-connected mode. This results in some reverse faults failing to trigger protection action; furthermore, the lack of auxiliary criteria makes it difficult to effectively distinguish between fault current and normal load current, leading to high false alarm and missed alarm rates. This invention addresses the problems of protection failure and high false alarm rates in off-grid mode by optimizing the protection criteria for off-grid mode to adapt to the low-current fault characteristics of inverter-type distributed generation and the bidirectional power flow characteristics of microgrids. Specifically, this invention employs a dual criterion of "low-amplitude overcurrent + voltage drop," eliminating the directional criterion and adapting to the low-current fault characteristics of inverter-type distributed generation and the bidirectional power flow characteristics of microgrids.

[0051] When the pattern recognition result indicates a switching transient mode, the adaptive protection decision layer calls the switching transient setting library, blocks the main protection, and only activates the overcurrent instantaneous trip protection (3 times the rated current, 0ms delay) and overvoltage / undervoltage protection to suppress the switching inrush current. It should be noted that the protection time limits for grid-connected mode, off-grid mode, and switching transient mode can be set according to actual conditions; specific examples are not provided here.

[0052] This invention implements mode-specific adaptive protection logic, designing independent protection setting libraries, action criteria, and time limits for each of the three operating modes, thus solving the problems of maloperation in grid-connected mode, failure to operate in off-grid mode, and transient instability during switching. This invention also achieves accurate identification of the three states of microgrids: grid-connected, off-grid, and switching transients, matching corresponding protection logic to each state to avoid maloperation and failure to operate during switching transients.

[0053] This invention utilizes a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating state, determining the microgrid's pattern recognition result. Then, based on a set mapping strategy, it determines the target relay protection strategy corresponding to the pattern recognition result. The set mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively. Thus, this invention clearly divides the microgrid's operating state into three modes—grid-connected, off-grid, and switching transient (0~200ms)—through hybrid islanding detection, rather than the traditional binary mode, providing a foundation for mode-specific protection. Furthermore, this invention designs independent relay protection strategies for each of the three operating modes, solving the problems of false tripping in grid-connected mode, failure to trip in off-grid mode, and instability during switching transients. Therefore, this invention solves the problem of the lack of switching transient protection logic in the mode-specific relays of existing microgrid dual-mode operation.

[0054] In other aspects of the embodiments of the present invention, the method of using a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating status to determine the pattern recognition result of the microgrid includes: using a passive detection method to perform preliminary detection based on the electrical quantities and the operating status to obtain preliminary detection results; when the preliminary detection results indicate that the switch of the common coupling point is closed and the electrical quantity is not within a preset threshold range, using an active detection method to perform multiple islanding detections on the microgrid to obtain multiple islanding detection results; and determining the pattern recognition result of the microgrid based on the matching result of the multiple islanding detection results and the comprehensive mode conditions; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

[0055] The passive detection method is the same as described above and will not be repeated here. In the active detection phase of this invention, the microgrid's pattern recognition result can be determined based on the matching results of the multiple islanding detection results and the integrated mode conditions. Determining the microgrid's pattern recognition result based on the matching results of the multiple islanding detection results and the integrated mode conditions includes: determining the microgrid's pattern recognition result as grid-connected mode when all multiple islanding detection results match the mode conditions of the grid-connected mode; determining the microgrid's pattern recognition result as off-grid mode when all multiple islanding detection results match the mode conditions of the off-grid mode; and determining the microgrid's pattern recognition result as a switching transient mode when all multiple islanding detection results match the mode conditions of the switching transient mode.

[0056] For example, if multiple consecutive islanding detection results show that the switch at the common coupling point is closed, and when a high-frequency disturbance is injected, the high-frequency disturbance component of the system is quickly absorbed by the main grid, and the electrical quantities such as voltage, frequency, and phase remain within the preset threshold range after a brief fluctuation and stabilization, then the microgrid's pattern recognition result is determined to be grid-connected mode. If multiple consecutive islanding detection results show that the switch at the common coupling point is open, and when a high-frequency disturbance is injected, the high-frequency disturbance component of the system cannot be quickly absorbed by the small power supply alone, the waveform fluctuates significantly, and the electrical quantities such as voltage, frequency, and phase deviate from the preset threshold range, then the microgrid's pattern recognition result is determined to be off-grid mode. If multiple consecutive islanding detection results show that the disturbance response is continuously changing and the waveform is unstable, then the microgrid's pattern recognition result is determined to be switching transient mode. This embodiment of the invention improves the accuracy of pattern recognition by verifying multiple islanding detection results.

[0057] In other aspects of the embodiments of the present invention, after determining the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy, the method further includes: in the case of a fault in the main grid, sending a trip command to the fault isolation layer to drive the switch corresponding to the fault to trip; in the case that the fault clearance state is not cleared, controlling the switch corresponding to the fault to remain in the tripped state; in the case that the fault clearance state is cleared, jumping to the step of using the hybrid islanding detection method to perform islanding detection based on the electrical quantity and the operating state to determine the pattern recognition result of the microgrid and re-executing the pattern recognition and relay protection strategy determination.

[0058] The adaptive protection decision layer performs fault judgment. Based on the matched protection logic, it judges the fault based on the electrical quantity data of the real-time collected common coupling point, distinguishing between three situations: no fault, minor fault, and serious fault. For example, in this embodiment of the invention, a comprehensive criterion of "voltage as the main factor, current and frequency as secondary factors, and rate of change and direction as supplementary factors" can be selected. When all electrical quantities fluctuate within the steady-state allowable range, for example, voltage: 0.95~1.05pu; frequency: 49.8~50.2 Hz; current: below the protection setting; voltage / current change rate: low, it is determined to be no fault. When electrical quantities experience acceptable, brief, and limited deviations, for example, voltage dip: 0.7~0.85pu, lasting <1s; frequency deviation: 48.5~49.8Hz or 50.2~51.0Hz; current: 1.1~1.5 times the rated value; rate of change: moderate, it is determined to be a minor fault. When electrical quantities deviate significantly, continuously, and jeopardize equipment stability, such as severe voltage drops / interruptions (<0.5 pu or close to 0), severe frequency exceeding limits (<47.5 Hz or >51.5 Hz), current exceeding 1.5~2 times the rated value (short-circuit characteristics), or extremely high rate of change (abrupt change), a serious fault is identified. Fault handling and isolation then proceed. If no fault is detected, the process returns to step 100, continuously monitoring the operating status. If a fault is detected, a trip command is sent to the collaborative control layer according to the hierarchical time limit rules. The collaborative control layer drives the corresponding switch of the execution unit in the fault isolation layer to trip, completing the selective isolation of the fault section and preventing the fault from escalating. The core of the collaborative control layer is the collaborative control unit, which includes a DG control mode switching module, a PCC switch control module, and a transient blocking control module. The core function of this layer is to receive control signals from the adaptive protection decision layer and the operating mode perception layer, coordinate the opening and closing actions of the PCC switch, the control mode switching of the distributed power supply, and the protection blocking logic during the switching transient period, ensuring that the switching process is consistent with the protection action sequence. The core of the fault isolation layer is the execution unit, which includes feeder switches, bus switches, and solid-state circuit breakers. The core function of this layer is to receive instructions from the coordinated control layer and execute tripping operations according to hierarchical and time-limited rules to achieve precise isolation of the faulty section and prevent fault escalation. Finally, protection reset is performed. After fault isolation, it is determined whether the fault has been cleared: if not, the tripping status of the corresponding switch is maintained and continuously monitored; if cleared, step 200 is re-executed to identify the current operating mode, reset the protection logic, and restore normal protection for the corresponding mode, thus closing the process loop. This embodiment of the invention achieves precise fault location and selective isolation, avoiding cascading tripping.

[0059] In other aspects of the embodiments of the present invention, the method further includes: in the event of a grid-connected / off-grid switching, coordinating the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid.

[0060] This invention, through a collaborative control layer, receives control signals from the adaptive protection decision layer and the operation mode perception layer. It coordinates the opening and closing actions of the PCC switch, the switching of control modes of distributed power sources, and the protection blocking logic during switching transients, ensuring that the switching process is consistent with the timing of protection actions. This invention implements a collaborative timing mechanism for off-grid switching and relay protection, achieving synchronous linkage between protection settings, action criteria, PCC switch actions, and distributed power source control mode switching, thereby improving the safety and stability of the switching process.

[0061] The embodiments of this invention construct a collaborative timing mechanism for grid-connected and off-grid handover and protection, which is divided into two branches: grid-connected to off-grid (unplanned islanding) and off-grid to grid-connected (planned overlap), and also includes a common branch for fault handling during the handover process.

[0062] In one embodiment, the coordinated timing mechanism for grid-connected to off-grid transition is as follows: In the event of a grid-connected / off-grid switching, the coordination of the opening and closing actions of the common coupling point switch, the switching of the control mode of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: when there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using a hybrid islanding detection method, sending a common coupling point opening command to the common coupling point switch, and switching the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the switching transient mode; switching the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode; and after a first set time threshold has elapsed, switching the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode.

[0063] The grid-connected to off-grid branch A represents unplanned islanding triggered by a main grid fault. The specific steps include: Step A1: When an anomaly or fault occurs in the main grid, the operation mode sensing layer detects that the voltage and frequency at the PCC exceed the grid-connected mode threshold; Step A2: The hybrid islanding detection module starts detection based on the electrical quantities and operating status of the common coupling point, confirms the islanding status within ≤5ms, and sends a tripping command for the common coupling point to the collaborative control layer; Step A3: Then, the collaborative control layer triggers the tripping of the common coupling point switch (using a solid-state circuit breaker, action time <5ms), and simultaneously sends a transient signal to the adaptive protection decision layer (triggering the relay protection strategy corresponding to the transient mode), triggering the main protection lockout (lockout duration 50ms, i.e., the first set time threshold), to prevent maloperation of the protection due to switching inrush current. Step A4: Next, the collaborative control layer synchronously switches the control mode of the distributed power source from PQ control (constant power control mode) to V / f control (constant voltage and constant frequency control mode) to maintain the stability of voltage and frequency within the microgrid; Step A5: After the 50ms transient ends, the adaptive protection decision layer automatically switches to off-grid protection logic (triggering the relay protection strategy corresponding to the off-grid mode), loads the off-grid protection settings, and puts in low-amplitude overcurrent + voltage auxiliary criteria; Step A6: Finally, the microgrid enters the normal off-grid operation state, and the protection system continuously monitors for faults.

[0064] In existing technologies, islanding detection is only used to trigger PCC switch operation. The detection result is not directly linked to the protection logic adjustment, resulting in a delay in protection mode switching after islanding is detected. During the transient period, the fault cannot be handled in a timely manner, which can easily lead to the escalation of the fault. The embodiments of this invention design a hybrid islanding detection and protection linkage scheme, which achieves rapid identification of islanding status (≤5ms) and directly triggers protection mode switching while avoiding power quality pollution, thus shortening the fault response time.

[0065] In one embodiment, the coordinated timing mechanism of the off-grid to grid-connected branch B is as follows: In the event of a grid-connected / off-grid switchover, coordinating the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: when the electrical quantity of the main grid meets the set grid-connection requirements, controlling the distributed power source to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within a set error range; sending a common coupling point closing command to the common coupling point switch, and switching the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode at the instant the common coupling point switch closes; switching the control mode of the distributed power source from a constant voltage and constant frequency control mode to a constant power control mode; and after a second set time threshold has elapsed, switching the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the grid-connected mode.

[0066] Branch B represents the off-grid to grid-connected transition (planned overlap, triggered by main grid recovery). The specific steps include: Step B1: The main grid returns to normal, and the operation mode sensing layer detects that the main grid voltage, frequency, and phase meet the grid connection requirements; Step B2: The collaborative control layer initiates pre-synchronization adjustment, controlling the distributed power source to adjust the microgrid's voltage, frequency, and phase, ensuring that the voltage difference between the microgrid and the main grid is <2%, the frequency difference is <0.1Hz, and the phase difference is <5°; Step B3: After the pre-synchronization conditions are met, the collaborative control layer triggers the common coupling point switch to close; Step B4: At the moment of closing, the adaptive protection decision layer switches to the relay protection strategy corresponding to the off-grid mode, i.e., blocking the off-grid low-set protection (when blocked). Step B5: Simultaneously switch the control mode of the distributed power source from V / f control (constant voltage and constant frequency control mode) to PQ control (constant power control mode) to restore power grid connection; Step B6: After the 100ms (second set time threshold) transient ends, the adaptive protection decision layer automatically switches to grid connection protection logic (switches to the relay protection strategy corresponding to the grid connection mode), loads the grid connection protection setting, and restores the directional inverse time overcurrent protection; Step B7: The microgrid enters the normal grid connection operation state, and the protection system continuously monitors the fault.

[0067] Existing technologies lack a clear understanding of the blocking, switching, and reset sequence of protection during switching operations, leading to conflicts between PCC switch actions and protection tripping actions. This results in issues such as cascading trips and power outages in non-fault areas, failing to guarantee uninterrupted power supply to critical loads during switching. This invention constructs a coordinated timing mechanism for off-grid switching and relay protection, achieving synchronous linkage between protection settings, action criteria, PCC switch actions, and distributed power supply control mode switching, thus improving the safety and stability of the switching process. This invention constructs a "blocking-switching-reset" timing mechanism to achieve synchronous linkage between PCC switch actions, distributed power supply control mode switching, and protection setting switching, suppressing switching impacts and avoiding timing chaos. Furthermore, it employs a three-stage inverse-time protection system, setting the action time limit in the order of feeder → bus → PCC, achieving precise fault location and selective isolation, and preventing cascading trips.

[0068] In one embodiment, the common branch (general during the handover process) is as follows: if a fault is detected during the handover process from grid-connected to off-grid or from off-grid to grid-connected, instantaneous fast-break protection is immediately activated (delay 0ms), and the execution unit of the fault isolation layer is driven by the collaborative control layer to isolate the faulty section; after the fault isolation is completed, the remaining handover steps are executed, and the protection logic of the corresponding mode is restored after the handover is completed, so as to ensure that the fault can be handled quickly during the handover process and to avoid the fault from expanding.

[0069] In summary, this invention proposes an adaptive relay protection method for the switching process between microgrids and grid connections. The core of this method is the construction of a comprehensive protection system encompassing "three-state identification—adaptive protection—cooperative control—fault isolation." Specifically, it offers the following five beneficial effects: 1. Accurate identification of three-state operation modes: The microgrid operation status is clearly divided into three types: grid-connected, off-grid, and switching transient (0~200ms), instead of the traditional binary mode. It achieves 5ms-level fast identification through hybrid islanding detection, providing a foundation for mode-specific protection.

[0070] 2. Mode-specific adaptive protection logic: Independent protection setting libraries, action criteria, and time limits are designed for the three operating modes to solve the problems of false operation in grid-connected mode, failure to operate in off-grid mode, and transient instability during switching.

[0071] 3. Coordinated timing of grid-connected and off-grid switching and protection: Construct a timing mechanism of "blocking-switching-reset" to realize the synchronous linkage of PCC switching action, distributed power supply control mode switching and protection setting switching, suppress switching impact and avoid timing chaos.

[0072] 4. Optimization of off-grid mode protection criteria: The dual criteria of "low-amplitude overcurrent + voltage drop" are adopted, and the direction criterion is eliminated to adapt to the low-current fault characteristics of inverter-type distributed power sources and the bidirectional power flow characteristics of microgrids.

[0073] 5. Hierarchical fault isolation: Three-stage inverse time protection is adopted, with the operating time set in the order of feeder → bus → PCC, to achieve accurate fault location and selective isolation, and avoid cascading tripping.

[0074] Device Examples Please refer to Figure 2 On the other hand, embodiments of the present invention also provide a relay protection device for a microgrid, comprising: The acquisition module 201 is used to acquire electrical quantities and operating status at the common coupling point of the microgrid; The detection module 202 is used to perform islanding detection based on the electrical quantities and the operating status using a hybrid islanding detection method to determine the pattern recognition result of the microgrid; the hybrid islanding detection method is constructed based on a passive detection method and an active detection method; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode; The determining module 203 is used to determine the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy; the set mapping strategy includes the relay protection strategies corresponding to the grid-connected mode, the off-grid mode and the switching transient mode respectively.

[0075] Optionally, the method of using a hybrid islanding detection approach to perform islanding detection based on the electrical quantities and the operating status, and to determine the pattern recognition result of the microgrid, includes: A preliminary detection method is used to perform initial detection based on the electrical quantities and operating status to obtain preliminary detection results; If the preliminary detection results indicate that the switch at the common coupling point is closed and the electrical quantity is not within the preset threshold range, the microgrid is subjected to multiple islanding detections using an active detection method to obtain multiple islanding detection results. Based on the matching results of the multiple islanding detections and the comprehensive mode conditions, the mode recognition result of the microgrid is determined; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

[0076] Optionally, determining the microgrid pattern recognition result based on the matching result of the multiple island detection results and the comprehensive pattern conditions includes: If the results of the multiple islanding detections all match the mode conditions of the grid-connected mode, the mode recognition result of the microgrid is determined to be the grid-connected mode. If the results of the multiple island detections all match the mode conditions of the off-grid mode, the mode recognition result of the microgrid is determined to be off-grid mode. If the results of the multiple island detections all match the mode conditions of the switching transient mode, the mode recognition result of the microgrid is determined to be the switching transient mode.

[0077] Optionally, determining the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy includes: When the pattern recognition result is a grid-connected mode, the target relay protection strategy corresponding to the grid-connected mode is determined to be to call the grid-connected protection setting library, use directional inverse time overcurrent protection as the main protection, and use undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current of the grid connection, and the direction criterion is that the fault current direction points to the line. When the pattern recognition result is an off-grid mode, the target relay protection strategy corresponding to the off-grid mode is determined to be to call the off-grid protection setting library, adopt amplitude inverse time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, cancel the direction criterion, and set the operating current according to the set multiple range of the rated current of the distributed power source. If the pattern recognition result is a switching transient mode, the target relay protection strategy corresponding to the switching transient mode is determined to be to call the switching transient setting library, block the main protection, and only activate the overcurrent instantaneous trip protection and overvoltage protection or the overcurrent instantaneous trip protection and undervoltage protection.

[0078] Optionally, the device further includes: The first control module is used to send a trip command to the fault isolation layer to drive the switch corresponding to the fault to trip when there is a fault in the main grid; when the fault clearance status is not cleared, it controls the switch corresponding to the fault to remain in the tripped state; when the fault clearance status is cleared, it jumps to the step of using the hybrid islanding detection method to perform islanding detection based on the electrical quantity and the operating status to determine the pattern recognition result of the microgrid and re-executes the pattern recognition and relay protection strategy determination.

[0079] Optionally, the device further includes: The coordination module is used to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid in the event of grid-to-off-grid switching.

[0080] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using the hybrid islanding detection method, a common coupling point trip command is sent to the common coupling point switch, and the target relay protection strategy corresponding to the microgrid is switched to the relay protection strategy corresponding to the transient mode. Switch the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode. After the first set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the off-grid mode.

[0081] Optionally, the coordination of the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching corresponding to the microgrid in the event of a grid-to-offline switching includes: When the electrical quantity of the main grid is detected to meet the set grid connection requirements, the distributed power source is controlled to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within the set error range. Send a common coupling point closing command to the common coupling point switch, and at the instant the common coupling point switch closes, switch the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode; Switch the control mode of the distributed power source from constant voltage and constant frequency control mode to constant power control mode; After the second set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the grid-connected mode.

[0082] The relay protection device of the microgrid includes a processor and a memory. The aforementioned acquisition module 201, detection module 202, and determination module 203 are all stored as program units in the memory. The processor executes these program units stored in the memory to achieve the corresponding functions. The processor contains a kernel, which retrieves the corresponding program units from the memory. One or more kernels may be provided. The memory may include non-permanent memory in computer-readable media, random access memory (RAM), and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. The memory includes at least one memory chip.

[0083] On the other hand, please refer to Figure 3 The present invention also provides a relay protection system for a microgrid, comprising: The operation mode perception layer 10 is used to collect electrical quantities and operating status of the microgrid's common coupling point; it uses a hybrid islanding detection method to perform islanding detection based on the electrical quantities and operating status to determine the microgrid's mode recognition result; the hybrid islanding detection method is constructed based on passive detection method and active detection method; the mode recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode; The adaptive protection decision layer 20 is used to determine the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy; the set mapping strategy includes the relay protection strategies corresponding to the grid-connected mode, the off-grid mode and the switching transient mode respectively.

[0084] The collaborative control layer 30 is used to receive control signals from the operation mode perception layer 10 or the adaptive protection decision layer 20 in the event of a grid-connected / off-grid switching, so as to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid.

[0085] In one embodiment, specifically, the relay protection system of the microgrid of this invention consists of an operation mode sensing layer 10, an adaptive protection decision layer 20, a collaborative control layer 30, a fault isolation layer 40, and a human-machine interaction and back-end unit 50. Each layer of modules works collaboratively to achieve adaptive protection throughout the entire process of microgrid grid-to-grid and off-grid switching. The specific architecture is described below: 1. Connection between main grid and microgrid: The main grid is connected to the microgrid bus through a common coupling point (PCC, including PCC switch). The PCC is the core interface for the microgrid to switch between grid connection and off-grid operation. Its closed state corresponds to grid connection operation, and its open state corresponds to off-grid operation.

[0086] 2. Microgrid core unit: The microgrid bus connects distributed generation units (including photovoltaic, energy storage, converters, etc.) and load units respectively. Distributed generation units can switch control modes (PQ control / V / f control) according to the operating mode. Load units include important loads and general loads to realize the supply and consumption of electrical energy.

[0087] 3. Operation Mode Sensing Layer 10: The core is the mode sensing unit, which includes a voltage acquisition module, a frequency acquisition module, a phase acquisition module, a PCC switch status monitoring module, and a hybrid islanding detection module. The core function of this layer is to acquire electrical quantities (voltage U, current I, frequency f, phase θ) at the PCC and the microgrid bus in real time, as well as the PCC switch status. Through the hybrid islanding detection module, it completes the accurate identification of the operation mode (grid-connected, off-grid, switching transient) and transmits the acquired signals and mode identification signals to the adaptive protection decision layer 20.

[0088] 4. Adaptive Protection Decision Layer 20: The core is the adaptive protection decision unit, which includes a pattern recognition module, a grid-connected setting library, an off-grid setting library, a switching transient setting library, and a time-limit coordination module. The core function of this layer is to receive signals from the pattern perception layer, lock the current operating mode through the pattern recognition module, call protection settings and action criteria from the corresponding setting library, calculate the action time limit through the time-limit coordination module, generate protection control signals, and transmit them to the cooperative control layer 30.

[0089] 5. Cooperative Control Layer 30: The core is the cooperative control unit, which includes the DG control mode switching module, the PCC switch control module, and the transient blocking control module. The core function of this layer is to receive control signals from the adaptive protection decision layer 20, coordinate the opening and closing actions of the PCC switch, the control mode switching of the distributed power supply, and the protection blocking logic during the switching transient period, so as to ensure that the switching process is consistent with the protection action sequence.

[0090] 6. Fault Isolation Layer 40: The core is the execution unit, which includes feeder switches, bus switches, and solid-state circuit breakers. The core function of this layer is to receive instructions from the coordinated control layer 30, execute tripping operations according to the hierarchical and time-limited rules, achieve precise isolation of faulty sections, and prevent the fault from escalating.

[0091] 7. Human-computer interaction and back-end unit 50: Used to realize functions such as operation mode display, protection setting, fault recording, and remote debugging, so as to facilitate operation and maintenance personnel to monitor the system operation status in real time and troubleshoot faults.

[0092] The relay protection system of this microgrid is used to execute the relay protection method for microgrids described in the above-described method embodiments. Since this relay protection system for microgrids adopts all the technical solutions of the above-described relay protection method for microgrids, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here.

[0093] On the other hand, the present invention also provides a computer program product (not shown), which includes a computer program that can be stored on a machine-readable storage medium. When the computer program is executed by a processor, the computer can execute a relay protection method for a microgrid. The method includes: collecting electrical quantities and operating status at the common coupling point of the microgrid; performing islanding detection based on the electrical quantities and operating status using a hybrid islanding detection method to determine the pattern recognition result of the microgrid; the hybrid islanding detection method is constructed based on a passive detection method and an active detection method; the pattern recognition result is one of a grid-connected mode, an off-grid mode, and a switching transient mode; determining a target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy; the set mapping strategy includes relay protection strategies corresponding to the grid-connected mode, the off-grid mode, and the switching transient mode, respectively.

[0094] In another aspect, the present invention also provides a machine-readable storage medium (not shown) storing a computer program thereon, which, when executed by a processor, implements a relay protection method for a microgrid. The method includes: acquiring electrical quantities and operating status at the microgrid's common coupling point; performing islanding detection based on the electrical quantities and operating status using a hybrid islanding detection method to determine the microgrid's pattern recognition result; the hybrid islanding detection method being constructed based on a passive detection method and an active detection method; the pattern recognition result being one of a grid-connected mode, an off-grid mode, and a switching transient mode; and determining a target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy; the set mapping strategy includes relay protection strategies corresponding to the grid-connected mode, the off-grid mode, and the switching transient mode, respectively.

[0095] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0096] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A relay protection method for a microgrid, characterized in that, include: Collect electrical quantities and operating status at the common coupling point of the microgrid; A hybrid islanding detection method is used to perform islanding detection based on the electrical quantities and the operating status, and the pattern recognition result of the microgrid is determined. The hybrid island detection method is constructed based on passive and active detection methods; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode. The target relay protection strategy corresponding to the pattern recognition result is determined based on the set mapping strategy. The mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively.

2. The relay protection method for microgrids according to claim 1, characterized in that, The method of using a hybrid islanding detection approach to perform islanding detection based on the electrical quantities and the operating status, and to determine the pattern recognition result of the microgrid, includes: A preliminary detection method is used to perform initial detection based on the electrical quantities and operating status to obtain preliminary detection results; If the preliminary detection results indicate that the switch at the common coupling point is closed and the electrical quantity is not within the preset threshold range, the microgrid is subjected to multiple islanding detections using an active detection method to obtain multiple islanding detection results. Based on the matching results of the multiple islanding detections and the comprehensive mode conditions, the mode recognition result of the microgrid is determined; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

3. The relay protection method for microgrids according to claim 2, characterized in that, The determination of the microgrid pattern recognition result based on the matching result of the multiple island detection results and the comprehensive pattern conditions includes: If the results of the multiple islanding detections all match the mode conditions of the grid-connected mode, the mode recognition result of the microgrid is determined to be the grid-connected mode. If the results of the multiple island detections all match the mode conditions of the off-grid mode, the mode recognition result of the microgrid is determined to be off-grid mode. If the results of the multiple island detections all match the mode conditions of the switching transient mode, the mode recognition result of the microgrid is determined to be the switching transient mode.

4. The relay protection method for microgrids according to claim 1, characterized in that, The step of determining the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy includes: When the pattern recognition result is a grid-connected mode, the target relay protection strategy corresponding to the grid-connected mode is determined to be to call the grid-connected protection setting library, use directional inverse time overcurrent protection as the main protection, and use undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current of the grid connection, and the direction criterion is that the fault current direction points to the line. When the pattern recognition result is an off-grid mode, the target relay protection strategy corresponding to the off-grid mode is determined to be to call the off-grid protection setting library, adopt amplitude inverse time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, cancel the direction criterion, and set the operating current according to the set multiple range of the rated current of the distributed power source. If the pattern recognition result is a switching transient mode, the target relay protection strategy corresponding to the switching transient mode is determined to be to call the switching transient setting library, block the main protection, and only activate the overcurrent instantaneous trip protection and overvoltage protection or the overcurrent instantaneous trip protection and undervoltage protection.

5. The relay protection method for microgrids according to claim 1, characterized in that, After determining the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy, the method further includes: In the event of a fault in the main network, a trip command is sent to the fault isolation layer to drive the corresponding switch to trip. If the fault is not cleared, the switch corresponding to the fault is controlled to remain in the tripped state. If the fault clearance status is cleared, the process jumps to the step of using a hybrid islanding detection method to perform islanding detection based on the electrical quantities and the operating status, and determining the microgrid pattern recognition result, and then re-executes the pattern recognition and relay protection strategy determination.

6. The relay protection method for microgrids according to claim 1, characterized in that, The method further includes: In the event of grid-connected / off-grid switching, coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid.

7. The relay protection method for microgrids according to claim 6, characterized in that, In the event of a grid-to-off-grid switchover, the coordination of the opening and closing actions of the common coupling point switch, the switching of the control mode of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: When there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using the hybrid islanding detection method, a common coupling point trip command is sent to the common coupling point switch, and the target relay protection strategy corresponding to the microgrid is switched to the relay protection strategy corresponding to the transient mode. Switch the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode. After the first set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the off-grid mode.

8. The relay protection method for microgrids according to claim 6, characterized in that, In the event of a grid-to-off-grid switchover, the coordination of the opening and closing actions of the common coupling point switch, the switching of the control mode of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: When the electrical quantity of the main grid is detected to meet the set grid connection requirements, the distributed power source is controlled to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within the set error range. Send a common coupling point closing command to the common coupling point switch, and at the instant the common coupling point switch closes, switch the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode; Switch the control mode of the distributed power source from constant voltage and constant frequency control mode to constant power control mode; After the second set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the grid-connected mode.

9. A relay protection device for a microgrid, characterized in that, include: The data acquisition module is used to collect electrical quantities and operating status at the common coupling point of the microgrid; The detection module is used to perform islanding detection based on the electrical quantities and the operating status using a hybrid islanding detection method, and to determine the pattern recognition result of the microgrid. The hybrid island detection method is constructed based on passive and active detection methods; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode. The determination module is used to determine the target relay protection strategy corresponding to the pattern recognition result based on the set mapping strategy; The mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively.

10. The relay protection device for a microgrid according to claim 9, characterized in that, The method of using a hybrid islanding detection approach to perform islanding detection based on the electrical quantities and the operating status, and to determine the pattern recognition result of the microgrid, includes: A preliminary detection method is used to perform initial detection based on the electrical quantities and operating status to obtain preliminary detection results; If the preliminary detection results indicate that the switch at the common coupling point is closed and the electrical quantity is not within the preset threshold range, the microgrid is subjected to multiple islanding detections using an active detection method to obtain multiple islanding detection results. Based on the matching results of the multiple islanding detections and the comprehensive mode conditions, the mode recognition result of the microgrid is determined; the comprehensive mode conditions include the mode conditions of grid-connected mode, the mode of off-grid mode, and the mode conditions of switching transient mode.

11. The relay protection device for a microgrid according to claim 10, characterized in that, The determination of the microgrid pattern recognition result based on the matching result of the multiple island detection results and the comprehensive pattern conditions includes: If the results of the multiple islanding detections all match the mode conditions of the grid-connected mode, the mode recognition result of the microgrid is determined to be the grid-connected mode. If the results of the multiple island detections all match the mode conditions of the off-grid mode, the mode recognition result of the microgrid is determined to be off-grid mode. If the results of the multiple island detections all match the mode conditions of the switching transient mode, the mode recognition result of the microgrid is determined to be the switching transient mode.

12. The relay protection device for a microgrid according to claim 9, characterized in that, The step of determining the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy includes: When the pattern recognition result is a grid-connected mode, the target relay protection strategy corresponding to the grid-connected mode is determined to be to call the grid-connected protection setting library, use directional inverse time overcurrent protection as the main protection, and use undervoltage protection and over-frequency / under-frequency protection as backup protection. The operating current is set according to the maximum short-circuit current of the grid connection, and the direction criterion is that the fault current direction points to the line. When the pattern recognition result is an off-grid mode, the target relay protection strategy corresponding to the off-grid mode is determined to be to call the off-grid protection setting library, adopt amplitude inverse time overcurrent protection combined with voltage drop auxiliary criterion as the main protection, cancel the direction criterion, and set the operating current according to the set multiple range of the rated current of the distributed power source. If the pattern recognition result is a switching transient mode, the target relay protection strategy corresponding to the switching transient mode is determined to be to call the switching transient setting library, block the main protection, and only activate the overcurrent instantaneous trip protection and overvoltage protection or the overcurrent instantaneous trip protection and undervoltage protection.

13. The relay protection device for a microgrid according to claim 9, characterized in that, The device further includes: The first control module is used to send a trip command to the fault isolation layer to drive the corresponding switch to trip when there is a fault in the main grid; when the fault clearance status is not cleared, it controls the corresponding switch to remain in the tripped state; when the fault clearance status is cleared, it jumps to the step of using the hybrid islanding detection method to perform islanding detection based on the electrical quantity and the operating status to determine the microgrid pattern recognition result and re-executes the pattern recognition and relay protection strategy determination.

14. The relay protection device for a microgrid according to claim 9, characterized in that, The device further includes: The coordination module is used to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the target relay protection strategy switching of the microgrid in the event of grid-connected or off-grid switching.

15. The relay protection device for a microgrid according to claim 14, characterized in that, In the event of a grid-to-off-grid switchover, the coordination of the opening and closing actions of the common coupling point switch, the switching of the control mode of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: When there is a fault in the main grid and the microgrid is determined to be in off-grid mode based on the electrical quantities and the operating status using the hybrid islanding detection method, a common coupling point trip command is sent to the common coupling point switch, and the target relay protection strategy corresponding to the microgrid is switched to the relay protection strategy corresponding to the transient mode. Switch the control mode of the distributed power source from constant power control mode to constant voltage and constant frequency control mode. After the first set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the off-grid mode.

16. The relay protection device for a microgrid according to claim 14, characterized in that, In the event of a grid-to-off-grid switchover, the coordination of the opening and closing actions of the common coupling point switch, the switching of the control mode of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid includes: When the electrical quantity of the main grid is detected to meet the set grid connection requirements, the distributed power source is controlled to adjust the difference between the electrical quantity of the microgrid and the electrical quantity of the main grid within the set error range. Send a common coupling point closing command to the common coupling point switch, and at the instant the common coupling point switch closes, switch the target relay protection strategy corresponding to the microgrid to the relay protection strategy corresponding to the off-grid mode; Switch the control mode of the distributed power source from constant voltage and constant frequency control mode to constant power control mode; After the second set time threshold has elapsed, the target relay protection strategy corresponding to the microgrid will be switched to the relay protection strategy corresponding to the grid-connected mode.

17. A relay protection system for a microgrid, characterized in that, include: The operation mode sensing layer is used to collect electrical quantities and operating status at the common coupling point of the microgrid; A hybrid islanding detection method is used to perform islanding detection based on the electrical quantities and the operating status, and the pattern recognition result of the microgrid is determined. The hybrid island detection method is constructed based on passive and active detection methods; the pattern recognition result is one of the following: grid-connected mode, off-grid mode, and switching transient mode. An adaptive protection decision layer is used to determine the target relay protection strategy corresponding to the pattern recognition result based on a set mapping strategy. The mapping strategy includes relay protection strategies corresponding to grid-connected mode, off-grid mode, and switching transient mode, respectively.

18. The relay protection system for a microgrid according to claim 17, characterized in that, The system also includes: The collaborative control layer is used to receive control signals from the operation mode perception layer or the adaptive protection decision layer in the event of a grid-connected / off-grid switchover, so as to coordinate the opening and closing actions of the common coupling point switch, the control mode switching of the distributed power source, and the switching of the target relay protection strategy corresponding to the microgrid.

19. A machine-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the relay protection method for the microgrid as described in any one of claims 1 to 8.

20. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the relay protection method for the microgrid as described in any one of claims 1 to 8.

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