Multi-source hierarchical collaborative black-start method for hybrid micro-grid

Abstract

The invention discloses a multi-source hierarchical collaborative black-start method for a hybrid micro-grid, which belongs to the technical field of electric power, and comprises the following steps: carrying out initialization and state self-checking confirmation on the hybrid micro-grid, carrying out network cleaning, taking network-forming type energy storage as a first power supply, taking network-forming type photovoltaic as synchronous grid-connected power supply collaboration, and taking a diesel generator as a hot standby power supply; a no-load backbone power grid is established according to the starting sequence and function roles of the three power supplies, dynamic loads of a hybrid micro-grid monitoring system, a control system and a direct-current sub-grid are sequentially and orderly recovered, grid-forming photovoltaic power, load capacity expansion, a non-critical power supply and a multi-island power supply are sequentially and gradually connected to a grid, and a hybrid micro-grid structure is reconstructed; the method has the beneficial effects of high reliability, high success rate, quick and orderly recovery, high scene adaptability, capability of being copied and popularized and the like.

Description

Technical Field

[0001] This invention relates to the field of power technology, specifically to a multi-source hierarchical coordinated black start method for hybrid microgrids. Background Technology

[0002] The plateau region has a high density of small and medium-sized hydropower stations, and their dams are mostly located at the end of the power grid. They rely on long-distance transmission lines across complex terrain, making them susceptible to extreme weather and geological disasters, resulting in frequent failures. Moreover, the power grid at the end of the grid has significant weak characteristics, with low short-circuit capacity, insufficient rigidity, and poor voltage and frequency stability. It is difficult to meet the power quality requirements of critical loads such as gate hoists. Extreme power outages can easily trigger flood control risks and even lead to dam overflow accidents.

[0003] Currently, black-start technology mainly focuses on recovery processes dominated by a single type of power source (such as a standalone diesel generator or grid-connected energy storage), and related patents mostly involve general control strategies or grid connection methods. However, in the specific scenario of small, scattered, and remote hydropower dams, existing technologies face significant shortcomings: Poor power supply coordination: Currently, the power supply for hydropower dams (sluice gates) in China typically includes various heterogeneous power sources such as external power lines, grid-based energy storage, grid-based photovoltaic power, and diesel generators. If relying solely on external power lines, natural disasters in high-altitude areas may cause power outages. If relying solely on grid-based energy storage, it cannot start when the state of charge (SOC) is below a safe threshold (e.g., <50%). If relying solely on photovoltaic power, it will completely fail during periods without sunlight. If relying solely on diesel generators, there is a risk of mechanical failure or insufficient fuel leading to startup failure. In extreme cases, this could cause prolonged power outages for critical loads such as dam gate opening and closing, and communication monitoring, posing a threat to flood control safety. Furthermore, existing general black-start methods lack standardized coordinated startup sequences and logic for these diverse power sources, easily leading to chaotic recovery processes, power conflicts, and even black-start failures.

[0004] The process is disconnected from the scenario: the general process does not take into account the special characteristics of the load on the hydropower station dam (gatehead) (such as the need to restore the monitoring system before restoring the gate power). At the same time, it does not make full use of the unique "grid-type photovoltaic" in the system as a black start co-power source, and fails to form an optimal recovery path.

[0005] Insufficient reliability: The system lacks a black-start path design with primary and backup redundancy. When the primary starting power source (such as energy storage) fails, the system may be unable to recover on its own, making it difficult to meet the extremely high reliability requirements for power supply restoration of hydropower station dams (sluice gates). Summary of the Invention

[0006] The purpose of this invention is to provide a multi-source hierarchical coordinated black start method and system for hybrid microgrids, which solves the problem of coordinating three power sources with different characteristics—grid-based energy storage, grid-based photovoltaic, and diesel generators—in a weak grid environment, enabling them to coordinate their actions according to the optimal timing and logic, thereby achieving fast, orderly, and reliable black start and system reconfiguration, and ensuring that the black start success rate of the core flood control facilities of the hydropower station dam (sluice gate) reaches 100% after extreme power loss.

[0007] This invention is achieved through the following technical solution: S1: Initialize and perform status self-check of the hybrid microgrid, and perform network cleanup; S2: The grid-connected energy storage is the primary power source, the grid-connected photovoltaic power source is the synchronous grid-connected power source, and the diesel generator is the hot backup power source. The unloaded backbone power grid is established according to the start-up order and functional roles of the three power sources. S3: Sequentially and orderly restore the power loads of the hybrid microgrid monitoring system, control system, and DC subgrid; S4: Gradually connect grid-connected photovoltaic systems, load expansion and non-critical power sources, and multi-island power sources to the grid, and reconstruct the hybrid microgrid structure.

[0008] In the above technology, in step S1, when a complete loss of power in the external power grid is detected and confirmed after a set delay, a black start is initiated, including: Detect the status of the grid-type energy storage system to confirm that the state of charge of its energy storage units is higher than the safety threshold and that the equipment self-test is normal. Automatically disconnect all non-critical load switches and disconnect all grid-connected circuit breakers of grid-connected power supplies to form a passive, clean, isolated network awaiting recovery.

[0009] In the above technology, in step S2, when the grid-type energy storage inverter receives the start command, it switches to voltage-frequency control mode to gradually establish and stabilize the rated power supply and frequency on the designated bus using a predetermined soft-start curve.

[0010] In the above technologies, the grid-type energy storage can be replaced by a power source with grid-building capability and voltage-frequency control mode, and the grid-type photovoltaic can be replaced by a distributed power source with grid-building capability.

[0011] In the above technology, step S3, where power supply is restored according to a preset load priority after the backbone power grid stabilizes, includes: First priority: Close the power switches of the monitoring system, communication equipment, protection devices, and energy management system to restore system control; The second priority is to restore the DC subsystem and supply power to the DC monitoring and communication modules.

[0012] In the above technology, during the S3 process, the grid-type energy storage is independently supported, and the diesel generator is in a hot standby state.

[0013] In the above technology, step S4 includes the following stages: When the energy management system detects that the backbone grid has been operating stably for more than a set time, it sends a grid connection permission command to the grid-connected photovoltaic inverter. Load expansion and grid connection of non-critical power sources: After the grid-connected photovoltaic system is successfully connected, the system will gradually put secondary AC loads into operation based on the power balance situation. In the multi-island parallel reconfiguration, when there is another independent island in the system that has been successfully black-started by a diesel generator, the synchronizing device detects that the voltage, frequency, and phase difference meet the conditions and automatically closes the interconnection switch to complete the network reconfiguration.

[0014] In the above technology, when a grid-type energy storage fails to start or exits abnormally during process S2 or S3, the system automatically or manually switches to a backup process using a diesel generator as the black start power source, repeating the logic process from S2 to S4.

[0015] In the above technology, when the system enters black start or islanded operation state, the energy management system or islanded detection device sends a mode switching command to each protection unit, and the protection device automatically switches the setting value to the low short-circuit capacity islanded setting value group.

[0016] In the aforementioned technology, when the protection device detects a fault and initiates the tripping logic, it simultaneously sends a fault signal to the grid-connected energy storage inverter. The grid-connected inverter immediately switches modes and limits its output current to a set current range within a specified time to maintain the bus voltage.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: High reliability and high success rate: The "first-start-hot-standby" dual-path design solves the problem of black start failure caused by a single power supply failure. In the field verification at the Yadu Hydropower Station, the black start success rate reached 100%.

[0018] Rapid and orderly recovery: The standardized four-stage process and clear power coordination sequence avoid blindness and conflict in the recovery process, and significantly shorten the total time from total power failure to core load recovery.

[0019] High adaptability to various scenarios: The recovery sequence is specially designed for the load characteristics of hydropower station dams, where "control takes precedence over power". It also innovatively introduces "grid-type photovoltaic" as an important supporting power source in the middle stage of black start, which improves the green energy utilization rate and stability during the system recovery process.

[0020] Replicable and scalable: This method forms a standard operating procedure applicable to microgrids with heterogeneous grid power sources, which can be widely applied to other water conservancy facilities, remote mining areas, islands and other similar high-reliability power supply scenarios. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the system power grid structure in this embodiment; Figure 2 This is a diagram illustrating the black boot process. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0023] Example 1 This embodiment addresses the engineering challenge of a hydropower station dam operating with both AC and DC loads exhibiting significant differences in load characteristics. It proposes a deeply collaborative hybrid microgrid topology of "AC / DC coupling + multi-energy complementarity," as follows: Figure 1 As shown, this architecture, with the dual coupling of physical structure and functional logic as its core, achieves optimized energy allocation and efficient, stable energy flow.

[0024] In this embodiment of the hybrid microgrid, there is one backbone network and four subgrids, which are flexibly interconnected according to power characteristics and load demand. Through standardized electrical interfaces (circuit breakers, inverters, DC / DC modules) and customized control strategies, flexible and controllable bidirectional power flow between the subgrids is achieved. This includes: The AC backbone network is based on the 400V distribution system of a hydropower station dam, with parallel operation of bus sections I and II and a reliable structure equipped with automatic standby power transfer (BZT) functionality. A 100kW grid-connected photovoltaic inverter and a 5kW wind turbine inverter are both connected to bus section I as the primary self-generated power source. The 10kV self-generated power is stepped down by a transformer before being connected to the main power source. A 35kV local municipal power supply serves as a second backup power source. A 250kW diesel generator set is connected via a dedicated circuit breaker as the ultimate backup. This network supplies power to all AC loads and serves as a common platform for power exchange between sub-networks.

[0025] The grid-based subgrid, with its core composed of a grid-based energy storage system, is the technological cornerstone for the stable operation of this architecture. Its "grid-building" capability allows intermittent power sources such as wind and solar to maximize power generation "unrestricted," while the storage system assumes full responsibility for maintaining system stability, thus decoupling the conflict between power generation and stability. It possesses the following characteristics: Voltage and frequency reference source: When operating in an islanded environment, it simulates the characteristics of a synchronous generator, autonomously establishes and maintains a stable 400V bus voltage and 50Hz frequency, and provides a "synchronization signal" for all grid-connected equipment.

[0026] Inertia and damping support: Provides virtual inertia and damping for the system, significantly enhancing the system's anti-interference capability and effectively suppressing frequency and voltage fluctuations caused by impact loads such as motor startup.

[0027] Real-time power balancer: Through millisecond-level charging and discharging response, it can smooth out random fluctuations in wind and solar power output in real time, absorb or supplement power deficits caused by impact loads, and ensure instantaneous balance between power generation and consumption.

[0028] Black start engine: In extreme cases where the main grid loses power completely and the diesel engine cannot start, it can rely on its own energy storage to autonomously establish voltage frequency from a "no power" state and gradually restore power supply to the microgrid.

[0029] The grid-connected subgrid consists of 100kW photovoltaic and 5kW wind turbines, employing grid-connected inverters. It serves as the system's economical and green power source, but its output uncertainty needs to be balanced by grid-connected energy storage or the main grid. It operates in Maximum Power Point Tracking (MPPT) mode, aiming to maximize renewable energy capture and generation. It relies entirely on a stable voltage and frequency reference point provided by the main grid or grid-connected energy storage on the AC backbone.

[0030] The DC subgrid is constructed according to the DC load capacity. The DC subgrid is connected to the AC backbone grid via a 10kW grid inverter and has efficiency-enhancing capabilities, specifically: Direct drive for high efficiency. The communication equipment in the monitoring system, the switching power supply in the secondary cabinet, and LED lighting are essentially DC loads. The DC subnet can directly power them, eliminating the need for the multi-stage conversion links of traditional AC / DC or DC / AC->AC / DC, reducing losses by about 2%-5% per conversion.

[0031] Plug and play. DC load devices can also be directly connected to the DC bus without rectification. If expanding to include DC sources such as photovoltaics or small wind power, they can be directly connected to this DC bus without a separate inverter, simplifying the structure and reducing costs.

[0032] Power buffering. The photovoltaic storage units within the DC subgrid can act as a small buffer pool, smoothing out internal load fluctuations and reducing power impact on the AC backbone.

[0033] The tiered safety network, with the 10kV / 35kV mains power serving as the system's voltage and frequency benchmark and final power balance point in grid-connected mode, also acts as an economical backup power source; the 250kW diesel generator serves as the ultimate physical backup. It activates when the main grid fails and the stored energy is insufficient, providing stable base load power and can work in conjunction with grid-connected energy storage to complete more complex black-start sequences, enhancing the system's survivability.

[0034] In this embodiment, the capacity allocation among the networks is as follows: When wind and solar power are operating at full capacity but the load is relatively light, the grid-connected units need to be able to absorb the excess power or limit the power output of wind and solar power through control strategies to prevent themselves from overloading. Therefore, the minimum grid power configuration should meet the critical load requirement of 20kW.

[0035] Considering the economic applications of smoothing wind and solar fluctuations, carrying out intraday peak shaving and valley filling, and ensuring the intermittent operation of diesel generators, the actual energy storage capacity should be slightly higher than the minimum value. It is recommended to configure 50kWh to achieve a balance between safety and economy.

[0036] Under the condition of ensuring the stability of the isolated grid, the ratio of distributed photovoltaic grid-connected capacity (kW) to grid-connected capacity (kW) of the system can be taken as 1:10. This ensures that when wind and solar power are at full capacity, the system still has enough grid-connected power to dominate the grid characteristics, avoiding the risk of instability caused by an excessively high proportion of grid-connected power.

[0037] To maximize the utilization of renewable energy and ensure the stability of the isolated grid, this embodiment establishes a deep collaborative mechanism centered on EMS, encompassing "grid construction, grid following, and intelligent interaction." Addressing the challenge of microgrid recovery after extreme total power outages in weak grid environments, a microgrid black-start and system reconfiguration technology system, primarily based on grid-based energy storage, solves problems such as small short-circuit capacity in low-voltage isolated grids, difficulties in multi-source coordination, and variations in equipment start-up and shutdown characteristics in weak grid environments. This enables rapid and reliable system recovery from a "total power outage" state to safe and stable operation.

[0038] The black boot process is as follows: S1: Initialization and Status Self-Check Confirmation Phase When the system detects that the external power grid (10kV self-use power and 35kV mains power) has completely lost voltage and confirms this after a set delay, the black start procedure is initiated.

[0039] First, the system controller (EMS) or on-site operator confirms that the grid-type energy storage system has black start capability, checks that the state of charge (SOC) of the battery energy storage unit is higher than the safety threshold (set to >50% on-site), and checks that the energy storage system, control system, and key circuit breakers are in normal condition.

[0040] Subsequently, the system automatically or manually performs a "cleaning" operation, disconnecting all non-critical load switches and disconnecting the grid-connected circuit breakers of all grid-connected power sources (grid-connected photovoltaic inverters and wind turbine converters), forming a passive, clean islanded network to be restored, thus avoiding the impact of random loads or power sources on the voltage build-up process.

[0041] S2: Establishment phase of unloaded backbone power grid Upon receiving the start-up command, the grid-connected energy storage inverter switches to V / f (voltage-frequency) control mode to start up as the main voltage and frequency source of the system. Taking the 400V I-section bus of this project as the first target, the energy storage system gradually establishes and stabilizes the rated voltage (400V) and rated frequency (50Hz) on the bus through a preset soft-start curve. This stage verifies the grid-connected energy storage's ability to establish and precisely control the voltage as the system's "anchor point" under no-load conditions.

[0042] S3: Phase of Orderly Recovery of Critical Loads and DC Subgrid After the backbone grid voltage stabilizes, the loads are restored according to a preset priority order: First, turn off the power switches of the most critical loads that ensure the operation of the system's "brain"—the monitoring, communication, protection, and EMS secondary cabinets—to ensure the control system is restored. Next, the DC subsystem is restored: the AC side switch for the 10kW DC subnetwork is closed, the DC / DC module starts up, and a stable 220V DC bus is established on the DC side to supply power to key DC loads such as DC monitoring equipment and communication modules.

[0043] The innovation at this stage lies in restoring the DC subsystem by supplying power from the AC side, which ensures the continuity of power supply to the control system's "neural network" and provides a monitoring and command basis for subsequent recovery operations.

[0044] S4: Multi-source phased grid connection and system reconfiguration phase The EMS continuously monitors the stability of the bus voltage and frequency. Once a set threshold is reached (e.g., continuous stable operation for more than 1 minute with a fluctuation rate below ±0.5%), it begins to gradually restore distributed power generation. The EMS sends "grid connection permitted" commands to grid-connected photovoltaic inverters and wind turbine converters. After detecting stable and qualified voltage and frequency signals on the bus, these grid-connected inverters automatically execute the grid connection procedure and begin generating electricity. Based on the bus power balance, the EMS dynamically adjusts the energy storage output and, according to load importance, gradually connects other important AC loads to expand the system's power supply range.

[0045] If multiple independent black-start power sources exist within the system (e.g., a 400V II busbar in another area is successfully black-started by a diesel generator), multiple stable island subsystems are formed. When network reconfiguration is required, synchronization checks are performed on the two islands (e.g., 400V I and II sections) using a standby automatic transfer switch or manual mode. The voltage amplitude, frequency, and phase difference of the two busbars are accurately measured and compared. When all parameters meet the preset synchronization conditions (e.g., voltage difference <5%, frequency difference <0.1Hz, phase difference <10°), the tie switch between the two busbars is automatically or manually closed, achieving safe and smooth grid connection of the two islands, completing the system network reconfiguration, and significantly improving the overall power supply reliability and load-carrying capacity.

[0046] To prevent the risk of failure of a single black-start power supply, this embodiment proposes a multi-power supply collaborative black-start and reconfiguration strategy, which improves the robustness of the recovery process. Specifically: The dual black start path design, employing grid-connected energy storage and diesel generators, presupposes grid-connected energy storage as the primary black start power source, with the diesel generator serving as a backup. If the grid-connected energy storage fails to start, the system can automatically or manually switch to the diesel generator starting process. Once the diesel generator starts, it also follows a standardized process of establishing a backbone grid and gradually restoring load and power. This dual-path design ensures that, even in extreme circumstances, the system has at least one reliable starting method.

[0047] A multi-source collaborative synchronous grid connection and rapid reconfiguration logic has been developed for situations where multiple isolated power supply islands (such as island A restored by energy storage and island B restored by diesel generators) need to be merged for operation. This intelligent synchronous grid connection logic is integrated into an EMS or dedicated synchronizing device. It can automatically identify the characteristics (master-slave relationship, regulation capability) of the power sources on both sides to be connected, and automatically adjust the power source acting as the "slave" (such as adjusting the diesel generator speed and excitation) to actively track the "master" grid (such as the busbar supported by grid-type energy storage) in terms of voltage, frequency, and phase. This significantly shortens the synchronization adjustment time, enabling safe and rapid (target time < 2 minutes) automatic reconfiguration of multiple isolated subsystems, integrating the dispersed power supply islands into a unified and stable network.

[0048] This embodiment addresses the protection challenges posed by the small short-circuit capacity and significant differences in fault characteristics between isolated grid systems and traditional large power grids. It proposes an adaptive protection technology, specifically: To address the significant difference in short-circuit current levels between grid-connected and islanded operation modes for the same feeder, an innovative microprocessor-based protection device with adaptive switching capabilities for multiple setting groups was applied. When the system enters black-start or islanded operation, the EMS or islanded detection device sends a mode switching command to each protection unit. The protection device automatically switches its settings to a second set of setting groups specifically designed for islanded networks with low short-circuit capacity (e.g., reducing the instantaneous overcurrent protection setting and adjusting the overcurrent protection time limit). This ensures that the protection device can still sensitively and reliably detect faults even under small short-circuit current conditions in islanded networks.

[0049] To address the issue of conventional overcurrent protection failing to operate or experiencing excessive delays due to insufficient current during islanded grid faults, this embodiment deeply integrates protection and control. When the protection device detects a fault and initiates tripping logic, it simultaneously sends a fault signal to the grid-connected energy storage inverter. The grid-connected inverter immediately switches from normal operation mode to "active current limiting" mode, limiting its output current to 1.1-1.2 times the rated current within milliseconds, while simultaneously striving to maintain the bus voltage. The purpose is twofold: first, to provide a sufficiently large and stable short-circuit current to the upstream protection device, ensuring its rapid and selective tripping of the faulty branch; and second, to limit the impact of the fault current on the inverter itself and other equipment. After the fault is cleared, the grid-connected inverter quickly restores voltage and frequency support to the islanded grid system, ensuring a smooth system transition and preventing secondary power loss due to the fault.

[0050] Example 2 Taking the microgrid of a hydropower station dam as an example, combined with Figure 2 The process of this embodiment is explained as follows: Initial state: An extreme disaster causes a complete loss of power to both the 10kV self-use power supply and the 35kV mains power supply, and the microgrid enters a state of complete power failure.

[0051] Phase 1: The system EMS confirms power failure and automatically initiates the black start procedure. First, a self-check confirms that the 50kW / 50kWh grid-connected energy storage's SOC is 65%, indicating normal status. Then, the control system automatically disconnects non-critical load switches such as charging piles and disconnects the grid-connected circuit breaker of the 100kW grid-connected photovoltaic system.

[0052] Phase 2: The grid-type energy storage PCS receives the EMS command, switches to V / f mode, and smoothly establishes a 400V / 50Hz voltage on the 400V I-section bus within 30 seconds.

[0053] Phase Three: After the no-load busbar stabilizes, the following circuits are closed sequentially: ① Power supply to the central control room monitoring screen, server, and communication base station; ② Switch on the AC side of the DC subnet, establishing the DC busbar and supplying power to the DC protection devices. At this point, the core monitoring functions have been restored.

[0054] Phase Four: Step A: The EMS confirms that the grid has been operating stably for 1 minute and sends an unlocking command to the 10kW grid-connected photovoltaic inverter. The photovoltaic inverter is then connected to the I-section bus in grid-connected mode, begins generating electricity, and provides additional support.

[0055] Step B: With sufficient system power, some lighting and ventilation loads are gradually added. Subsequently, the 100kW grid-connected photovoltaic system detects a stable power grid and automatically connects to generate electricity.

[0056] Step C (not triggered in this case): Assume that the energy storage path is normal during this black start, and the diesel generator does not start. If the energy storage fails to start, the backup path will be triggered, and the diesel generator will act as the primary power source to repeat the above process.

[0057] Final state: Within approximately 5-8 minutes, the system recovers from a completely dark state to a stable islanded operation network that includes grid-connected energy storage, grid-connected photovoltaics, and grid-connected photovoltaics, with important loads such as gate hoists in a hot standby state that is readily available.

[0058] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-source hierarchical coordinated black-start method for hybrid microgrids, characterized in that, Includes the following steps: S1: Initialize and perform status self-check of the hybrid microgrid, and perform network cleanup; S2: The grid-connected energy storage is the primary power source, the grid-connected photovoltaic power source is the synchronous grid-connected power source, and the diesel generator is the hot backup power source. The unloaded backbone power grid is established according to the start-up order and functional roles of the three power sources. S3: Sequentially and orderly restore the monitoring system, control system, and DC subgrid power loads of the hybrid microgrid; S4: Gradually connect grid-connected photovoltaic systems, load expansion and non-critical power sources, and multi-island power sources to the grid, and reconstruct the hybrid microgrid structure.

2. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1, characterized in that, In step S1, after detecting a complete loss of power in the external power grid and confirming this after a set delay, a black start is initiated, including: Detect the status of the grid-type energy storage system to confirm that the state of charge of its energy storage units is higher than the safety threshold and that the equipment self-test is normal. Automatically disconnect all non-critical load switches and disconnect all grid-connected circuit breakers of grid-connected power supplies to form a passive, clean, isolated network awaiting recovery.

3. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1, characterized in that, In S2, when the grid-type energy storage inverter receives the start command, it switches to voltage-frequency control mode and gradually establishes and stabilizes the rated power and frequency on the designated bus using a predetermined soft-start curve.

4. A multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1 or 3, characterized in that, The grid-based energy storage can be replaced by a power source with grid-based capability and voltage-frequency control mode, and the grid-based photovoltaic can be replaced by a distributed power source with grid-based capability.

5. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1, characterized in that, In step S3, once the backbone power grid stabilizes, power supply is restored according to a preset load priority, including: First priority: Close the power switches of the monitoring system, communication equipment, protection devices, and energy management system to restore system control; The second priority is to restore the DC subsystem and supply power to the DC monitoring and communication modules.

6. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 5, characterized in that, During the S3 process, the grid-type energy storage provides independent support, and the diesel generator is in a hot standby state.

7. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1, characterized in that, S4 includes the following stages: When the energy management system detects that the backbone grid has been operating stably for more than a set time, it sends a grid connection permission command to the grid-connected photovoltaic inverter. Load expansion and grid connection of non-critical power sources: After the grid-connected photovoltaic system is successfully connected, the system will gradually put secondary AC loads into operation based on the power balance situation. In the multi-island parallel reconfiguration, when there is another independent island in the system that has been successfully black-started by a diesel generator, the synchronizing device detects that the voltage, frequency, and phase difference meet the conditions and automatically closes the interconnection switch to complete the network reconfiguration.

8. The multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 1, characterized in that, When a grid-type energy storage fails to start or exits abnormally during S2 or S3, the system automatically or manually switches to a backup process using a diesel generator as the black start power source, repeating the logic process from S2 to S4.

9. A multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 8, characterized in that, When the system enters black start or islanded operation mode, the energy management system or islanded detection device sends a mode switching command to each protection unit, and the protection device automatically switches the setting value to the low short-circuit capacity islanded setting value group.

10. A multi-source hierarchical coordinated black-start method for hybrid microgrids according to claim 9, characterized in that, When the protection device detects a fault and initiates the tripping logic, it simultaneously sends a fault signal to the grid-connected energy storage inverter. The grid-connected inverter immediately switches modes and limits its output current to a set current range within a specified time to maintain the bus voltage.

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