An Adaptive Off-Grid Coordinated Control System and Method for Microgrids with Multiple Connection Points

Abstract

A multi-connection-point microgrid adaptive off-grid coordinated control system and method are disclosed. The system includes a microgrid MGCC (Mechanical Management Control Center) deployed at each microgrid connection point and a microgrid feeder automation device for each bus section. All devices are interconnected via GOOSE networking communication. A dynamically selected MGCC co-control host executes a global coordinated control strategy. The MGCC co-control host can receive the switch positions and anti-islanding protection action information of the interconnected bus MGCCs. When the microgrid is disconnected planned or unplanned, the MGCC co-control host controls the tripping of the connection point switches and switches the loads to ensure the microgrid enters a stable off-grid operation state. The microgrid feeder automation device collects the positions of the feeders and tie switches on its own bus and can control the opening and closing of the switches. This application allows the microgrid to enter the off-grid operation state only after the islanding status is simultaneously identified at multiple connection points, reducing the risk of anti-islanding protection malfunction and achieving seamless switching between planned and unplanned microgrid off-grid operation.

Description

Technical Field

[0001] This application relates to the field of microgrid anti-islanding protection and coordinated control technology, and in particular to an adaptive off-grid coordinated control system and method for microgrids with multiple grid connection points. Background Technology

[0002] With the rapid development of renewable energy, microgrids, as an important form of efficient utilization of distributed energy, play a crucial role in improving power supply reliability and promoting the consumption of new energy. However, microgrids still face many technical challenges during grid-connected / off-grid switching, especially the off-grid control of microgrids with multiple grid connection points.

[0003] Traditional microgrids typically employ a single grid connection point structure, with off-grid control primarily relying on local anti-islanding protection devices to trip upon detecting grid anomalies and switch to off-grid operation. However, for microgrids with multiple grid connection points, relying solely on the anti-islanding protection of a single node may result in some grid connection points failing to disconnect in a timely manner, leading to asynchronous closing or islanding failure, thus affecting system stability. Furthermore, existing technologies lack a global coordination mechanism, making it difficult to achieve rapid source-load power balancing and coordinated control of energy storage devices during planned off-grid operations or passive disconnection due to grid faults, which can easily lead to microgrid instability and power outages.

[0004] Currently, some solutions use centralized controllers to achieve off-grid coordination of microgrids, but there are problems such as communication delays and single points of failure; while fully distributed control is difficult to guarantee the rapid synchronous judgment of the status of multiple grid-connected points, which may lead to protection malfunctions or difficulties in coordinated control.

[0005] Existing technologies, suitable for smooth switching control between planned and unplanned grid connection and disconnection in hybrid microgrids, do not consider system-level coordinated control and the instability of microgrid operation caused by excessive power deficit in unplanned disconnection scenarios. Grid-connected microgrid coordinated control systems and methods do not provide detailed explanations of the protection action logic of the grid-connected point RTU (Remote Terminal Unit) in the event of a fault outside the microgrid, and there is a communication delay between the MGCC (Micro Grid Central Controller) and the grid-connected point RTU, affecting the speed of control such as synchronization detection and closing or energy storage mode switching. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this application provides an adaptive off-grid coordinated control system and method for microgrids with multiple grid connection points, which solves the problem of seamless switching between planned and unplanned off-grid operations of microgrids with multiple grid connection points, and ensures stable off-grid operation of microgrids.

[0007] The technical solution adopted in this application is as follows.

[0008] The first aspect of this application provides an adaptive off-grid coordinated control system for a microgrid with multiple grid connection points, wherein the multiple grid connection points are located on interconnected bus segments, and at least one bus segment is connected to energy storage or grid-connected distributed power generation equipment. The system includes:

[0009] Microgrid coordination control devices are deployed at each grid connection point and microgrid feeder automation devices are deployed at each bus section; one microgrid coordination control device acts as the co-control master and the remaining microgrid coordination control devices act as co-control slaves.

[0010] In the active off-grid coordinated control mode, after the co-control host receives the active off-grid control command from the superior master station, the microgrid feeder automation device implements load switching. When the power of the grid connection point is adjusted to be less than the preset threshold value, the co-control host controls each co-control slave to turn off the corresponding grid connection switch and sends an off-grid operation success or failure signal to the superior master station.

[0011] In the unplanned off-grid coordinated control mode, when each slave device identifies an island within a set time, it trips the corresponding grid-connected switch and sends the island protection action signal to the master device. The master device then sends a power limit release command to the energy storage power conversion system and implements load switching through the microgrid feeder automation device. After achieving source-load balance within the microgrid, the master device sends an off-grid operation success or failure signal to the upper-level master station.

[0012] Optionally, it can be determined whether there are network-type devices connected to the grid connection point. If there are network-type devices connected, it can be dynamically determined whether the grid connection point should act as a co-control host based on the interconnection relationship between the bus and other bus of the grid connection point.

[0013] Optionally, the microgrid coordination control device and microgrid feeder automation device at each grid connection point are connected to the process layer and achieve horizontal communication through GOOSE networking.

[0014] Optionally, determine whether the grid connection point has network-type equipment connected. If network-type energy storage is connected, dynamically determine whether the grid connection point should act as a co-control host based on the interconnection relationship between the bus and other bus of the grid connection point, including:

[0015] Each microgrid coordination control device calculates the grid construction capacity based on the energy storage devices connected to its corresponding bus.

[0016] The communication link quality of the microgrid coordination control device is calculated based on the GOOSE communication delay and packet loss rate between the microgrid coordination control devices.

[0017] Prioritize each microgrid coordination and control device by comprehensively considering network construction capabilities and communication link quality.

[0018] The microgrid coordination control device receives the status of the tie switch through GOOSE to determine the interconnection status between this bus and other buses.

[0019] The microgrid coordination control device with the highest priority among the interconnected buses is selected as the co-control host; if the priorities are the same, the microgrid coordination control device with the smallest bus number is selected as the co-control host.

[0020] Optionally, each microgrid coordination control device calculates the grid construction capacity based on the energy storage devices connected to its corresponding bus, including:

[0021] Obtain the maximum output power of the energy storage device connected to the bus corresponding to each microgrid coordination control device;

[0022] Calculate the difference between the state of charge and the minimum allowable state of charge of the energy storage device connected to this bus, and calculate the product of the difference and the rated capacity of the grid-type energy storage.

[0023] Calculate the ratio of the product to the minimum operating time for critical loads;

[0024] The smaller of the maximum output power of the energy storage device connected to this bus and the ratio is taken as the network construction capability of each microgrid coordination control device.

[0025] Optionally, each microgrid coordination control device can monitor the voltage and frequency at its local grid connection point in real time. When all upstream power sources fail, the low voltage, low frequency, and frequency change rate at the grid connection point can be used as islanding criteria to identify the islanding status.

[0026] Each microgrid coordination control device uses negative sequence voltage, zero sequence voltage, and overcurrent as the blocking conditions for anti-islanding protection. When a short circuit or ground fault occurs inside or outside the zone, the fault is identified and the anti-islanding protection is blocked to prevent the anti-islanding protection from malfunctioning.

[0027] The second aspect of this application provides an adaptive off-grid coordinated control method for microgrids with multiple grid connection points, which operates in the aforementioned adaptive off-grid coordinated control system for microgrids with multiple grid connection points. The method includes steps of active off-grid coordinated control and unplanned off-grid coordinated control.

[0028] The steps of the active off-grid coordination control specifically include:

[0029] The upper-level master station sends an active off-grid control command to the co-control host. The co-control host controls the other co-control slaves to trip the grid connection switch at their respective bus. The co-control host performs multi-level load switching and adjusts the power of the grid connection point until it is less than the preset threshold value. The co-control host stops switching loads and trips the grid connection switch on its side, and sends a signal to the upper-level master station indicating whether the off-grid operation was successful or failed.

[0030] The steps of the unplanned off-grid coordination control specifically include:

[0031] Upon detecting a power failure at the upstream level, the slave device immediately trips its local grid connection switch and sends an islanding protection action signal to the master device. Upon detecting a power failure at the upstream level, the master device, after all other interconnecting bus grid connection point switches are disconnected, stores the current grid connection point power and trips its local grid connection switch. It then issues a power limit release command to the energy storage power conversion system, and, based on the grid connection point power deficit, switches the load in one go according to the preset priority, sending a successful or failed off-grid operation signal to the upstream master station.

[0032] Optionally, the method further includes adding fault identification interlocking logic to the anti-islanding protection, including:

[0033] When the co-control host detects a system fault, it sends a standby signal to the energy storage power conversion system and locks the anti-islanding protection logic, waiting for the reclosing delay to end. If a momentary fault occurs and the reclosing successfully restores power, the co-control host controls the energy storage to resume or stop operation based on the grid connection point voltage and frequency status. If a permanent reclosing failure occurs, resulting in power loss at the upstream level, the unplanned off-grid coordination control steps are executed.

[0034] Optionally, the steps of proactive off-grid coordination control specifically include:

[0035] The superior master station sends an active disconnection control command to the co-control host. Upon receiving the control command from the superior master station, the co-control host determines whether all the grid connection switches of the other interconnected bus grid connection points are disconnected. If not all are disconnected, the co-control host controls the other co-control slaves through GOOSE to trip the grid connection switch at their respective bus.

[0036] After all connections are disconnected, the co-control host determines the power of the grid connection point on this side. If the power is greater than the preset threshold, it controls the feeder automation device to switch on and off according to the preset load priority, ensuring that the power of the grid connection point is less than the preset threshold.

[0037] The co-control host stops switching resistors and trips the local grid-connected switch. It then checks whether the voltage and frequency of the microgrid are stable. If they remain stable, it determines that the microgrid is successfully operating off-grid and sends an off-grid operation success signal to the upper-level master station, and the microgrid enters the off-grid operation control mode. Otherwise, it sends an off-grid operation failure signal to the upper-level master station.

[0038] Optional, the steps for unplanned off-grid coordination control specifically include:

[0039] If the upstream power grid experiences a power outage, each slave device in the coordinated control unit will identify islanding operation based on the changes in electrical quantities at the grid connection point. After identifying islanding within a set time, each slave device in the coordinated control unit will immediately trip its own grid connection switch and send the islanding protection action signal to the coordinated control host.

[0040] After the host detects that the upper-level power is lost, it determines whether all interconnected slave busbars have been tripped based on the real-time topology. After all the grid connection point switches of the remaining interconnected busbars are disconnected, it stores the current grid connection point power and trips the grid connection switch on its own side.

[0041] After the islanding protection is activated, the co-control host sends a power limit release signal to the energy storage power conversion system. The energy storage operates at maximum output power. Based on the grid connection point power and energy storage power before the islanding protection is activated, the co-control host controls the feeder automation device through GOOSE to switch the load on and off, ensuring the source-load balance within the microgrid.

[0042] The co-control host determines whether the voltage and frequency on the microgrid side are stable. If they remain stable, it determines that the microgrid has successfully started off-grid operation and sends an off-grid operation success signal to the upper-level master station, and the microgrid enters the off-grid operation control mode; otherwise, it sends an off-grid operation failure signal to the upper-level master station.

[0043] A third aspect of this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded onto the processor, implements the above-described adaptive off-grid coordinated control method for microgrids with multiple grid connection points.

[0044] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described adaptive off-grid coordinated control method for microgrids with multiple grid connection points.

[0045] Compared with the prior art, the beneficial effects of this application include at least the following:

[0046] This application provides a coordinated control method for achieving smooth adaptive off-grid operation switching of a microgrid system with multiple grid-connected points. When the microgrid switches between grid-connected and off-grid operation states, it can quickly identify islands and perform power balance control on the grid-connected points, improving the accuracy and stability of the microgrid during planned or unplanned off-grid switching, and ensuring continuous power supply to important loads when the upper-level system fails.

[0047] This application utilizes the GOOSE fast communication protocol between devices and collaborative control to coordinate and control energy storage and loads, ensuring power supply to critical loads during unplanned off-grid operation. It enables rapid and seamless off-grid switching in microgrids with multiple grid connection points, reduces the risk of islanding protection malfunction, and ensures the stable operation of the microgrid after off-grid operation.

[0048] This application adopts an adaptive master-slave coordinated control architecture to replace the traditional centralized control method, which improves the adaptability of the coordinated control strategy to multi-connection point systems and the speed of control response.

[0049] This application presents a passive anti-islanding protection method based on multi-criteria collaboration, applicable to on-grid / off-grid switching scenarios and on-grid power balance control in microgrids with multiple on-grid points. In unplanned off-grid scenarios, millisecond-level fault identification and active power balance at on-grid points are achieved through collaborative master-slave control and global coordinated control of anti-islanding protection and source-load balance control, effectively ensuring power supply to important loads. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0051] Figure 1 This is a schematic diagram of the topology of an adaptive off-grid coordinated control system for a microgrid with multiple grid connection points, provided in an embodiment of this application.

[0052] Figure 2 This is a schematic diagram of an active off-grid coordination control process provided in an embodiment of this application;

[0053] Figure 3 A schematic diagram of an unplanned off-grid coordination and control process provided for an embodiment of this application;

[0054] Figure 4 This is a schematic diagram of an island detection principle provided in an embodiment of this application. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The embodiments described in this application are merely some embodiments of this application, and not all embodiments. Based on the spirit of this application, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this application.

[0056] Embodiment 1 of this application provides an adaptive off-grid coordinated control system for microgrids with multiple grid connection points, which is applied to a microgrid system with multiple grid connection points, wherein the multiple grid connection points are located on multiple interconnected bus sections, and at least one bus section is connected to an energy storage device.

[0057] It is worth noting that, in this application, a microgrid refers to a microgrid with multiple grid connection points, or a microgrid group with multiple grid connection points located on interconnected busbars. It is a microgrid group composed of multiple microgrids interconnected by busbars, wherein each microgrid has an independent grid connection point.

[0058] The adaptive off-grid coordinated control system for microgrids based on multiple grid connection points includes: an MGCC deployed at each grid connection point and a microgrid feeder automation device at each bus section. Examples, but not limited to, include... Figure 1 As shown, the adaptive off-grid coordinated control system for microgrids with multiple grid connection points is applied to a microgrid system with three grid connection points. The three grid connection points are located on three interconnected 10kV bus lines: bus I, bus II, and bus III. The 10kV bus II is connected to an energy storage device.

[0059] The MGCC and microgrid feeder automation devices at each grid connection point are all connected to the process layer and achieve horizontal communication through GOOSE (GenericObject Oriented Substation Event) networking.

[0060] The energy storage operates in VSG (Virtual Synchronous Generator) mode, enabling rapid grid construction support during the switching between microgrid and off-grid operation, ensuring power supply to critical loads.

[0061] Each MGCC monitors key electrical quantities such as voltage and frequency at its grid connection point in real time. When all upstream power supplies fail, the low voltage, low frequency, and frequency change rate at the grid connection point are used as islanding criteria to quickly identify the islanding status.

[0062] Each MGCC uses negative sequence voltage, zero sequence voltage, and overcurrent as the blocking conditions for anti-islanding protection operation. When a short circuit or ground fault occurs inside or outside the zone, it can quickly identify the fault and block the anti-islanding protection to prevent the anti-islanding protection from malfunctioning.

[0063] Furthermore, when a two-phase short-circuit fault occurs upstream of the MGCC, negative sequence voltage is used as the fault criterion; when a three-phase short-circuit fault occurs upstream of the MCGG, the grid connection point voltage temporarily drops, and when islanding occurs, since the hydropower units and VSG can provide instantaneous active and reactive power support, the grid connection point voltage gradually decreases to a steady state or becomes unstable according to different power differences, and low voltage with slip-ring blocking is used as the fault criterion; when a short-circuit fault occurs downstream of the MGCC, overcurrent is used as the fault criterion; when a ground fault occurs on the 110kV or 35kV side, negative sequence voltage is used as the fault criterion; when a ground fault occurs on the 10kV side, zero sequence voltage is used as the fault criterion; when all upstream power supplies fail, causing islanding, both frequency and voltage decrease, and low frequency, low voltage, and frequency change rate are considered as islanding criteria; one of the multiple MGCCs acts as the co-control master, and the remaining MGCCs at the grid connection point of the interconnected bus act as co-control slaves.

[0064] Preferably, but not restrictively, the MGCC determines the co-control host in real time based on the microgrid system topology and the grid-connected energy storage access.

[0065] Furthermore, the MGCC at the grid connection point with the smallest number and an energy storage access bus is selected as the coordination control host.

[0066] The system pre-determines whether the local area is connected to the energy storage network device through the pre-configured settings of the co-control device, judges the interconnection relationship between the local bus and other buses in real time, and dynamically determines whether to act as the co-control host.

[0067] Each microgrid coordination control device calculates the grid construction capacity based on the energy storage devices connected to its corresponding bus, including:

[0068] Obtain the maximum output power of the energy storage device connected to the bus corresponding to each microgrid coordination control device;

[0069] Calculate the difference between the state of charge and the minimum allowable state of charge of the energy storage device connected to this bus, and calculate the product of the difference and the rated capacity of the grid-type energy storage.

[0070] The ratio of the product to the minimum operating time of critical loads is calculated, and the smaller of the maximum output power of the energy storage device connected to the corresponding bus and the ratio is taken as the network construction capability of each microgrid coordination control device.

[0071] Specifically, the grid capacity of each MGCC is calculated based on the energy storage devices connected to its bus, using the following formula:

[0072] C a = min(P) max , ( SOC current - SOC min ) E rated / t ）

[0073] in, C a This indicates the networking capability of each MGCC. max This indicates the maximum output power of grid-type energy storage. current Indicates the current state of charge. min Indicates the minimum permissible state of charge. E rated t represents the rated capacity of grid-type energy storage, and t represents the minimum operating time to ensure critical loads.

[0074] Understandably, the maximum power that grid-connected energy storage can generate under conditions of at least continuous power supply time t is compared with the rated maximum output power of the energy storage to determine the grid-connection capability in real time.

[0075] Specifically, the MGCC communication link quality is calculated based on the GOOSE communication delay and packet loss rate between MGCCs:

[0076]

[0077] in, Indicates the quality of the MGCC communication link. The normalized value representing the average delay of the GOOSE heartbeat between MGCCs. This represents the normalized value of the maximum GOOSE communication delay between the current MGCC and other MGCCs. This represents the normalized value of the packet loss rate. If H is less than 0, it is forcibly set to 0, indicating a communication failure.

[0078] The communication link quality of MGCCs is calculated based on the GOOSE communication delay and packet loss rate between MGCCs; the priority of each MGCC is determined by comprehensively considering network construction capability and communication link quality.

[0079] The MGCC receives the status of the tie switch through GOOSE to determine the interconnection status between this bus and other buses; it selects the MGCC with the highest priority among the interconnected buses as the co-control master; if the priorities are the same, the MGCC with the smaller bus number is selected as the co-control master.

[0080] Taking into account network construction capabilities and communication link quality, the priority of each MGCC is determined as follows:

[0081] The network construction capabilities and communication link quality of each MGCC are normalized.

[0082] The comprehensive priority score is obtained by weighting the normalized network construction capability, communication link quality, and the weights of network construction capability and communication link quality:

[0083] P Score =λ×Norm( C a )+(1-λ)×Norm(H)

[0084] Among them, P Score To calculate the overall priority score, Norm( C a ) for MGCC's network construction capabilities C a The normalized value of , Norm(H) is the normalized value of the MGCC communication link quality H, and λ is C a The weight.

[0085] The priority of each MGCC is determined based on the overall priority score, and the one with the highest overall priority score is selected as the co-control host.

[0086] In this embodiment, the system can automatically complete the master re-election under operating conditions such as hot-swapping of energy storage, switching of bus connection, and communication interruption, without the need for manual adjustment of master-slave relationship.

[0087] The MGCC co-control host receives the tie-line switch status collected by the microgrid feeder automation device through the process layer, and judges the bus interconnection status in real time.

[0088] The microgrid feeder automation device can collect the status of each feeder and tie switch and send it to the MGCC (Mechanical Management Control Center) of the main bus. Control priorities are preset for each feeder load based on its importance level.

[0089] like Figure 2 As shown, in the active off-grid coordinated control mode, the MGCC co-control host is used to receive active off-grid control commands from the superior master station, control the other MGCC co-control slaves through GOOSE, and trip the grid connection switch at the bus where it is located; adjust the power of the grid connection point to below the preset threshold value through multi-level load switching, trip the grid connection switch on this side, and send a signal indicating successful or failed off-grid operation to the superior master station based on whether the voltage and frequency on the microgrid side are stable.

[0090] The MGCC slave device is used to receive control from the MGCC master device via GOOSE and trip the grid connection switch at its bus.

[0091] The microgrid feeder automation device is used to receive control from the MGCC co-control host via GOOSE and to switch loads on and off according to preset load priorities.

[0092] like Figure 3 As shown, in the unplanned off-grid coordinated control mode, if the upstream power grid loses power, each MGCC, including the MGCC co-control host and each MGCC co-control slave, is used to detect key electrical quantity characteristics such as voltage and frequency at the local grid connection point in real time. When all upstream power sources lose power, the low voltage, low frequency and frequency change rate at the grid connection point are used as islanding criteria to quickly identify the islanding status.

[0093] Each MGCC slave device is used to immediately trip its local grid-connected switch after identifying an island within a set time, and send the island protection action signal to the MGCC master device.

[0094] After identifying the island, the MGCC co-control host receives the status of the grid connection points of the other interconnected buses, records the power deficit of the grid connection point and trips the grid connection point switch on its side, issues a power limit release command to the energy storage PCS, and switches the loads in one go according to the preset priority based on the power deficit of the grid connection point to ensure that the microgrid enters the stable off-grid operation state. Based on whether the voltage and frequency on the microgrid side are stable, it sends a signal to the upper-level master station indicating whether the off-grid operation is successful or failed.

[0095] Energy storage is used to operate at maximum output power after receiving a power limit release signal.

[0096] The microgrid feeder automation device is used to receive control from the MGCC co-control host via GOOSE to switch loads on and off.

[0097] like Figure 4 As shown, to prevent the anti-islanding protection from malfunctioning due to grounding or short-circuit faults in the system, fault identification and blocking logic is added to the anti-islanding protection. The MGCC co-control host is used to identify grounding or short-circuit faults in the system, send a standby signal to the energy storage PCS and block the anti-islanding protection logic. The MGCC co-control host enters the normal control logic or the unplanned off-grid coordination control mode depending on whether the reclosing is successful.

[0098] Embodiment 2 of this application provides an adaptive off-grid coordination control method for microgrids with multiple grid connection points. Specifically, it is an off-grid coordination control method for microgrids based on GOOSE communication, which operates on the adaptive off-grid coordination control system for microgrids with multiple grid connection points as described in Embodiment 1. Through collaborative judgment of the status of multiple grid connection points and global load optimization management, it achieves seamless switching between planned and unplanned off-grid operations, improving the power supply reliability and flexible networking capability of the microgrid. The adaptive off-grid coordination control method for microgrids with multiple grid connection points includes: steps of active off-grid coordination control, steps of unplanned off-grid coordination control, and, in order to prevent the anti-islanding protection from malfunctioning due to grounding or short-circuit faults in the system, fault identification blocking logic is added to the anti-islanding protection.

[0099] like Figure 2 As shown, the steps of proactive off-grid coordination control specifically include:

[0100] Step 1.1: The upper-level master station sends an active disconnection control command to the MGCC co-control host. Upon receiving the control command from the upper-level master station, the MGCC co-control host determines whether all the grid connection switches of the other interconnected bus points are disconnected. If all are disconnected, proceed to step 1.2. If not all are disconnected, the MGCC co-control host controls the other MGCC co-control slaves through GOOSE to trip the grid connection switches at their respective bus points. After all are disconnected, proceed to step 1.2.

[0101] For example, but not limited to, if Figure 1 If the grid connection switches of bus I and bus III are not disconnected, the MGCC co-control host will control the other MGCC co-control slaves to trip their grid connection switches via GOOSE.

[0102] Preferably, but not restrictively, each MGCC determines its coordinating control host in real time based on the microgrid system topology and the grid-connected energy storage. Further, the MGCC with the smallest number and the grid connection point with grid-connected energy storage is selected as the coordinating control host. The MGCC most recently configured as the coordinating control host communicates with the superior master station.

[0103] Step 1.2: The MGCC co-control host performs multi-level load switching and adjusts the power of the grid connection point until it is less than the preset threshold value, then continues to execute step 1.3.

[0104] Specifically, the MGCC co-control host determines the power of the local grid connection point. If the power of the local grid connection point is greater than the preset threshold value, it controls the feeder automation device to switch on and off according to the preset load priority, so as to ensure that the power of the grid connection point is less than the preset threshold value.

[0105] Preferably, but not restrictively, the preset threshold value can be set as a set percentage of the rated energy storage capacity.

[0106] For example, but not limited to, 10% of the rated energy storage capacity, to reduce the impact on energy storage equipment when switching to active off-grid operation.

[0107] Step 1.3: The MGCC co-control host stops switching resistors and trips the local grid-connected switch. It then determines whether the voltage and frequency of the microgrid are stable. If they remain stable, the microgrid is considered to be successfully operating off-grid. The host sends an off-grid operation success signal to the upper-level master station, and the microgrid enters the off-grid operation control mode. Otherwise, the host sends an off-grid operation failure signal to the upper-level master station.

[0108] like Figure 3 As shown, the specific steps of unplanned off-grid coordination control include:

[0109] Step 2.1: After the MGCC slave device detects the power failure of the upstream unit, it immediately trips the local grid connection switch and sends the islanding protection action signal to the MGCC master device. After the MGCC master device detects the power failure of the upstream unit, it determines whether all interconnected slave busbars have tripped based on the real-time topology. After all other interconnected busbar grid connection point switches are disconnected, it stores the current grid connection point power and trips the local grid connection switch.

[0110] Specifically, if a power outage occurs in the upstream power grid, each MGCC slave device quickly identifies islanding operation based on changes in key electrical quantities such as voltage and frequency at the grid connection point. After identifying islanding within a set time, each MGCC slave device immediately trips its own grid connection switch. Preferably, but not limited to, each MGCC slave device identifies islanding within 60ms and immediately trips its own grid connection switch, and sends the islanding protection action signal to the MGCC master device.

[0111] Step 2.2: After identifying the island, the MGCC co-control host determines the status of the grid connection point switches of the other interconnected buses. If all are disconnected, it records the power deficit of the grid connection point and trips the grid connection point switch on its side.

[0112] Step 2.3: After the MGCC co-control host trips the grid connection switch, it issues a power limit release command to the energy storage PCS. Based on the power deficit at the grid connection point, it switches the loads in one go according to the preset priority to ensure that the microgrid enters a stable off-grid operation state.

[0113] Specifically, after the islanding protection is activated, the MGCC co-control host sends a power limit release signal to the energy storage PCS, and the energy storage operates at maximum output power. Based on the grid connection point power and energy storage power before the islanding protection is activated, the MGCC co-control host controls the feeder automation device through GOOSE to switch the load on and off, ensuring the source-load balance within the microgrid, enabling the microgrid to stably enter the off-grid operation state and ensuring the power supply to important loads.

[0114] Step 2.4: The MGCC co-control host determines whether the voltage and frequency on the microgrid side are stable. If they remain stable, it determines that the microgrid has successfully started off-grid operation and sends an off-grid operation success signal to the upper-level master station, and the microgrid enters the off-grid operation control mode; otherwise, it sends an off-grid operation failure signal to the upper-level master station.

[0115] More specifically, at T0+40ms, the co-control master and slave devices detect a power failure at the upstream level. The co-control slave immediately trips its local grid-connected switch and receives a switch detachment signal at T0+50ms to determine islanding. Simultaneously, it sends an islanding protection action signal to the master via a GOOSE message. At T0+60ms, the master receives the status of all slave devices. At T0+70ms, after determining that all other interconnected bus grid-connected switches have been disconnected, it trips its local grid-connected switch and simultaneously issues an unlocking power limit execution command. At T0+80ms, the master begins to perform a one-time load switching according to priority and continuously monitors the stability of the microgrid's voltage and frequency.

[0116] In this embodiment, all nodes are coordinated by the host to avoid asynchronous operations. The GOOSE message has a time stamp and acknowledgment mechanism to achieve closed-loop control. From detection to execution, the entire process takes less than 200ms and does not rely on IEEE1588 time synchronization. It has zero additional hardware cost and achieves seamless switching.

[0117] like Figure 4 As shown, to prevent the anti-islanding protection from malfunctioning due to grounding or short-circuit faults in the system, fault identification and blocking logic is added to the anti-islanding protection, including the following steps:

[0118] Step 3.1: When the MGCC co-control host detects a grounding or short-circuit fault in the system, it immediately sends a standby signal to the energy storage PCS and blocks the anti-islanding protection logic, waiting for the reclosing delay to end.

[0119] Preferredly but not restrictively, to prevent failure of asynchronous reclosing, the anti-islanding protection blocking delay can be set in conjunction with the circuit breaker reclosing time.

[0120] Step 3.2: After the reclosing delay ends, the MGCC co-control host determines whether the reclosing is successful after the anti-islanding protection logic is unlocked. If a momentary fault occurs and the reclosing successfully restores power supply, continue to step 3.3; otherwise, jump to step 3.4.

[0121] Step 3.3: If a momentary fault occurs and the reclosing successfully restores power supply, the MGCC co-control host determines that the grid connection point voltage and frequency have returned to normal, and issues an operation command to the energy storage PCS, and the energy storage resumes normal operation; if the grid connection point voltage and frequency are abnormal, a shutdown command is issued to the energy storage PCS.

[0122] Step 3.4: If a permanent reclosing failure occurs, resulting in power loss at the upstream level, the MGCC co-control host determines that the grid connection point voltage and frequency have returned to normal. After the MGCC at each grid connection point identifies the islanding operation status, it enters the anti-islanding protection coordination control logic. That is, it executes the steps of unplanned off-grid coordination control.

[0123] As one of the key features of this application, it dynamically selects the MGCC co-control host to execute a global coordinated control strategy based on the bus number and the grid-connected energy storage equipment. The MGCC co-control host can receive the switch positions and anti-islanding protection action information from the interconnected bus MGCC co-control slaves. When the microgrid is disconnected from the grid in a planned or unplanned manner, the MGCC co-control host controls the tripping of the grid connection point switch and switches the loads to ensure that the microgrid enters a stable off-grid operation state. The microgrid feeder automation device collects the positions of the feeders and tie switches on the bus and can control the opening and closing of the switches. It is suitable for off-grid switching operation control of microgrids with multiple grid connection points. The microgrid only enters the off-grid operation state after multiple grid connection points simultaneously identify the islanding status, reducing the risk of anti-islanding protection malfunction and achieving seamless switching between planned and unplanned microgrid disconnection.

[0124] Embodiment 3 of this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements the adaptive off-grid coordinated control method for a microgrid with multiple grid connection points described in Embodiment 2.

[0125] Embodiment 4 of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements an adaptive off-grid coordinated control method for a microgrid with multiple grid connection points as described in Embodiment 2.

[0126] It is worth noting that in the embodiments disclosed herein, "steps + numbers" is merely an expression for clearly describing a specific implementation method of an adaptive off-grid coordinated control method for microgrids with multiple grid connection points, rather than an absolute restriction on the order of the steps. Under the guidance of the core concept of this invention, changing the order of these steps to achieve the same or similar technical effects all fall within the scope of this invention.

[0127] Embodiments of this application may be provided as methods, systems, or computer program products. Therefore, this application may take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application may be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0128] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0129] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0130] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0131] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0132] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A multi-point-of-grid microgrid adaptive off-grid coordinated control system, the multi-point-of-grid is located in interconnected multi-section bus, at least one section of bus accesses network type energy storage device, characterized in that, The system comprises: The micro-grid coordination control device deployed at each grid-connected point and the micro-grid feeder automation device at each section of bus; one micro-grid coordination control device as a coordination host, and the rest as coordination slaves; the micro-grid coordination control device at each grid-connected point and the micro-grid feeder automation device are connected to the process layer, and realize horizontal communication through GOOSE networking; In the active off-grid coordination control mode, after receiving the active off-grid control instruction from the upper master station, the coordination host controls the rest of the coordination slaves to open the grid-connected switch at the bus where the coordination slave is located, controls the micro-grid feeder automation device to implement load switching to adjust the power of the grid-connected point to less than the preset threshold, opens the grid-connected switch on the side, and sends the off-grid operation success or failure signal to the upper master station based on whether the micro-grid side voltage and frequency are stable; In the non-planned off-grid coordination control mode, each coordination slave opens the grid-connected switch on the side after identifying the island within the set time, and sends the island protection action signal to the coordination host; the coordination host opens the grid-connected switch on the side after identifying the island, issues a power limit release instruction to the energy storage power conversion system, controls the micro-grid feeder automation device to implement load switching according to the power shortage of the grid-connected point, and sends the off-grid operation success or failure signal to the upper master station based on whether the micro-grid side voltage and frequency are stable after the load switching is completed; The micro-grid feeder automation device is controlled by the coordination host through GOOSE, and is switched according to the preset load priority; Determine whether there is a grid-forming energy storage device connected to the grid-connected point, and in the case of a grid-forming energy storage device connected to the grid-connected point, dynamically determine whether the grid-connected point is the coordination host according to the interconnection relationship between the bus of the grid-connected point and other buses, including: Each micro-grid coordination control device calculates the grid-forming capability according to the grid-forming energy storage device connected to the bus; Calculate the communication link quality of the micro-grid coordination control device according to the GOOSE communication delay and packet loss rate between the micro-grid coordination control devices; Consider the grid-forming capability and communication link quality to determine the priority of each micro-grid coordination control device; The micro-grid coordination control device receives the status of the tie switch through GOOSE and determines the interconnection state of the bus with the rest of the buses; Select the micro-grid coordination control device with the highest priority among the interconnected buses as the coordination host; if the priorities are the same, preferentially select the micro-grid coordination control device with the smallest bus number as the coordination host.

2. The adaptive off-grid coordination control system based on multiple grid-connected points according to claim 1, wherein: Each micro-grid coordination control device calculates the grid-forming capability according to the grid-forming energy storage device connected to the bus, including: Obtain the maximum output power of the grid-forming energy storage device connected to the bus corresponding to each micro-grid coordination control device; Calculate the difference between the state of charge and the minimum allowable state of charge of the grid-forming energy storage device connected to the bus corresponding to each micro-grid coordination control device, and the product of the difference and the rated capacity of the grid-forming energy storage device; Calculate the ratio of the product to the minimum operating time of the important load; The smaller value between the maximum output power of the networked energy storage device corresponding to the bus to which the microgrid is connected and the ratio is taken as the network construction capability of each microgrid coordination control device. 3.The adaptive off-grid coordination control system based on multiple grid-connected points of a microgrid according to claim 1, characterized in that: Each microgrid coordination control device detects the voltage and frequency at the grid-connected point in real time, and takes the low voltage, low frequency and frequency change rate at the grid-connected point as the islanding criterion to identify the islanding state when all the upper power supplies are powered off. Each microgrid coordination control device takes the negative sequence voltage, zero sequence voltage and overcurrent as the anti-islanding protection action blocking condition, identifies the fault and blocks the anti-islanding protection when a short circuit or ground fault occurs in the area, and prevents the anti-islanding protection from malfunctioning.

4. An adaptive off-grid coordinated control method based on a multi-grid-connection-point microgrid, which is operated in the adaptive off-grid coordinated control system based on a multi-grid-connection-point microgrid according to any one of claims 1 to 3, characterized in that, The method comprises a step of active off-grid coordination control and a step of unplanned off-grid coordination control. The step of active off-grid coordination control specifically comprises: After the coordination master receives the active off-grid control instruction from the upper master station, it controls the remaining coordination slaves to open the grid-connected switch at the bus where the coordination slave is located, controls the microgrid feeder automation device to implement load switching to adjust the power at the grid-connected point to less than the preset threshold, opens the grid-connected switch at the bus, and sends an off-grid operation success or failure signal to the upper master station based on whether the voltage and frequency at the microgrid side are stable. The step of unplanned off-grid coordination control specifically comprises: When each coordination slave identifies an island within a preset time, it opens the grid-connected switch at the bus and sends an islanding protection action signal to the coordination master; the coordination master opens the grid-connected switch at the bus after identifying an island; the coordination master sends a power release instruction to the energy storage power conversion system, controls the microgrid feeder automation device to implement load switching according to the power deficiency at the grid-connected point, and sends an off-grid operation success or failure signal to the upper master station based on whether the voltage and frequency at the microgrid side are stable after the load switching is completed. 5.The adaptive off-grid coordination control method based on multiple grid-connected points of a microgrid according to claim 4, characterized in that: The method further comprises a fault identification blocking logic for the anti-islanding protection, comprising: When the coordination master identifies a system fault, it sends a standby signal to the energy storage power conversion system and blocks the anti-islanding protection logic, and waits for the reclosing delay to end; if the power supply is successfully restored after reclosing due to a transient fault, the coordination master controls the networked energy storage device to resume or stop operation according to the voltage and frequency at the grid-connected point; if the upper power supply is lost due to permanent reclosing failure, the step of unplanned off-grid coordination control is executed. 6.The adaptive off-grid coordination control method based on multiple grid-connected points of a microgrid according to claim 4 or 5, characterized in that: The step of active off-grid coordination control specifically comprises: The upper master station sends an active off-grid control instruction to the coordination master, and the coordination master receives the control instruction sent by the upper master station, judges whether the grid-connected switches at the remaining interconnected bus grid-connected points are all open, and if not, controls the remaining coordination slaves to open the grid-connected switch at the bus through GOOSE. After all the switches are opened, the coordination host judges the power of the grid-connected point, and if the power is greater than the preset threshold, the micro-grid feeder automation device is controlled to be switched according to the preset load priority, so as to ensure that the power of the grid-connected point is less than the preset threshold. The coordination host opens the grid-connected switch on the side, judges whether the voltage and frequency of the micro-grid side are stable, and if so, judges that the micro-grid off-grid operation is successful, sends an off-grid operation success signal to the upper master station, and the micro-grid enters the off-grid operation control mode; otherwise, an off-grid operation failure signal is sent to the upper master station.

7. The adaptive off-grid coordination control method for the multi-grid-connected point micro-grid according to claim 4 or 5, characterized in that: The steps of the non-planned off-grid coordination control specifically include: If the upper grid loses power, each coordination slave machine identifies island operation according to the change of the grid-connected point electrical quantity, opens the grid-connected switch on the side within a set time after identifying the island, and sends an island protection action signal to the coordination host; The coordination host opens the grid-connected switch on the side after identifying the island; After the coordination host sends the power release instruction to the energy storage power conversion system, the grid-forming energy storage device operates at the maximum output power, the coordination host controls the load to be switched by the micro-grid feeder automation device according to the power of the grid-connected point and the energy storage power before the island protection action, and ensures the source load balance in the micro-grid; After the load switching is completed, the coordination host judges whether the voltage and frequency of the micro-grid side are stable, and if so, judges that the micro-grid off-grid operation is successful, sends an off-grid operation success signal to the upper master station, and the micro-grid enters the off-grid operation control mode; otherwise, an off-grid operation failure signal is sent to the upper master station.

8. An electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The computer program is loaded into the processor to realize the adaptive off-grid coordination control method for the multi-grid-connected point micro-grid according to any one of claims 4-7.

9. A computer-readable storage medium storing a computer program, the computer program comprising instructions that, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 8. The computer program is executed by the processor to realize the adaptive off-grid coordination control method for the multi-grid-connected point micro-grid according to any one of claims 4-7.

Images