Direct-current micro-grid grading black-start method and system

Abstract

The invention discloses a grading black-start method and system for a direct-current micro-grid. The grading black-start method and system are applied to the direct-current micro-grid comprising one or more of an energy storage converter, a direct-current charging pile and a photovoltaic converter. According to the method, physical communication connection is not needed, and autonomous cooperation is achieved by monitoring the voltage state of a point of common coupling (PCC). In the first stage, short circuit or load power over-limit detection is carried out by outputting a first voltage threshold and combining a sampling error compensation algorithm; the second stage utilizes bus voltage characteristics to guide multiple devices to be autonomously put into operation to realize collaborative aggregation; and the third stage regulates and controls the bus voltage to climb to a target threshold value through closed-loop control. In addition, the system is combined with load priority management, loads are cut off when starting is blocked, and orderly recovery is achieved after starting is completed. According to the method, the problems that traditional black start depends on a communication link, parameters are solidified and are easily interfered by sampling errors are solved, and the starting flexibility and reliability of the direct-current micro-grid under the non-communication working condition are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and microgrid control technology, specifically relating to a hierarchical black-start method and system for DC microgrids. Background Technology

[0002] As a crucial carrier for renewable energy consumption and efficient power supply, the black-start capability of DC microgrids directly affects the system's power supply reliability. Existing DC microgrid black-start schemes typically suffer from the following technical problems: First, multi-device collaboration heavily relies on physical communication links (such as Ethernet and CAN bus). In remote scenarios where communication cables fail or there is no communication, the converters cannot work in coordination, leading to system failure.

[0003] Secondly, the startup parameters are fixed. The startup voltage threshold and detection time window in the existing solutions are mostly fixed values, which cannot be adapted to the differentiated characteristics of different devices such as energy storage converters (ESC), DC charging piles (DCC), and photovoltaic converters.

[0004] Furthermore, the startup logic lacks robustness. Traditional startup detection does not fully consider the noise floor and error of the hardware sampling circuit, and is prone to misjudging normal voltage fluctuations as short circuits. Moreover, when multiple devices are connected in parallel, there is a lack of a clear hierarchical coordination mechanism, which can easily lead to excessive circulating current or voltage instability. Summary of the Invention

[0005] The purpose of this invention is to address the technical problems in existing black-start schemes, such as reliance on physical interconnection for multi-device collaboration, fixed parameters, easy misjudgment of short-circuit detection, and unclear collaboration logic. This invention provides a black-start control method and system for multi-device collaboration without interconnection in DC microgrids, realizing autonomous collaborative startup of ESC, DCC, and photovoltaic converters without interconnection, thereby improving startup flexibility and reliability.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides a hierarchical black-start method for DC microgrids. The method includes: applying a method to a DC microgrid containing one or more devices, such as energy storage converters, DC charging piles, and photovoltaic converters, with each device connected in parallel to a common coupling point (PCC) at the DC bus terminal. The method does not require establishing physical communication connections between the devices; instead, it achieves autonomous coordination by monitoring the voltage state of the common coupling point, and includes the following steps: The first-level startup step involves controlling the target device to output a configurable first voltage threshold to the common coupling point and continuously monitoring it for a preset first duration. If the bus voltage reaches the first voltage threshold and no fault logic is triggered within the first duration, the short circuit detection is deemed successful, and the second-level startup step is initiated. If the bus voltage is continuously lower than a preset percentage of the first voltage threshold, a short circuit or overload power fault is determined, triggering the first fault flag and executing the fault handling procedure. The second-level startup step involves controlling the target device to maintain the bus voltage at or above the first voltage threshold, and waiting for other devices to autonomously start operation within a preset second time period to complete the coordinated assembly by sensing the bus voltage characteristics. If the bus voltage stabilizes above the preset second voltage threshold at the end of the second time period, the coordinated assembly is determined to be successful, and the third-level startup step is initiated. If the bus voltage drops below the second voltage threshold, the black start is determined to be a failure, and the second fault indicator is triggered. The third-level startup procedure is as follows: switch the control mode of the target device to closed-loop control, regulate the bus voltage to climb towards the configurable third voltage threshold, and continuously monitor the preset third duration; if the bus voltage reaches the third voltage threshold and the fluctuation range is within the allowable range, a startup completion status flag is generated; otherwise, a third fault flag is triggered.

[0007] In one or more embodiments of the present invention, the first voltage threshold, the second voltage threshold, and the third voltage threshold are configurable parameters stored in the device control unit; the first duration, the second duration, and the third duration are configurable time parameters set according to the device response characteristics.

[0008] In one or more embodiments of the present invention, the fault logic judgment rule in the first-level startup step is as follows: when the bus voltage is continuously lower than 5%-15% of the first voltage threshold within the first duration and is accompanied by a sudden change in output current, it is determined that there is a short circuit fault in the system; the fault handling process includes: correcting the sampling data by combining the preset voltage sampling error compensation value, and triggering the equipment protection mechanism after confirming the short circuit; if the voltage is still not established after the short circuit is eliminated, it is determined that the load power is over-limit, and the load is disconnected in the order of non-critical load priority and high-power load priority, and the first-level startup step is re-executed.

[0009] In one or more embodiments of the present invention, the autonomous coordination mechanism in the second-level startup step is specifically as follows: non-target devices in the microgrid monitor the voltage at the common coupling point, and when they identify that the voltage is stable above the first voltage threshold, they autonomously determine the black start requirement and start their own pre-charge or discharge program to participate in the bus voltage support; target devices determine whether multiple devices in the system have completed coordinated aggregation by detecting the steady-state maintenance time and voltage fluctuation characteristics of the bus voltage.

[0010] In one or more embodiments of the present invention, after generating the startup completion status flag, a load recovery process is also included: After the system has been running stably for a preset period of time, loads that were previously removed will be gradually connected based on load priority and device power parameters. The load access sequence follows the principle of "prioritizing core system loads, followed by critical social loads, and lastly general loads." After each load is accessed, voltage and current monitoring is performed for a preset observation period to confirm that there are no abnormal fluctuations before the next level of load is accessed.

[0011] In one or more embodiments of the present invention, differentiated load control strategies are configured for different device types: For DC charging piles, prioritize disconnecting low-priority charging interfaces and high-power charging modules. For photovoltaic converters, prioritize cutting off non-essential power output units; For energy storage converters, non-core energy storage support loads should be cut off first.

[0012] In another aspect of the present invention, a hierarchical black-start system for a DC microgrid is provided, comprising: The control unit is configured to execute the control method according to any one of claims 1 to 6, store configurable voltage thresholds and time parameters, and output a start control signal and a load regulation signal; The voltage and current monitoring module is configured to collect DC bus voltage and output current data, and then correct the data by combining the built-in sampling error compensation algorithm before feeding it back to the control unit; The autonomous collaboration module is configured to identify the system's black start requirements and the grid connection status of other devices by analyzing the amplitude and fluctuation characteristics of the bus voltage, and to achieve multi-device collaboration under the condition of no physical interconnection communication cables. The load management module is configured to receive control signals from the control unit and perform load disconnection and connection operations; The status identification module is configured to generate and output status codes and fault indicators during the startup process.

[0013] In one or more embodiments of the present invention, the voltage and current monitoring module has a built-in linear error compensation strategy to perform offline correction on the collected voltage signal, with a compensation range covering sampling error of ±0.5% to ±2%.

[0014] In one or more embodiments of the present invention, the conditions for the autonomous collaboration module to determine the completion of multi-device collaborative aggregation include: within the second time period, the bus voltage fluctuation amplitude is less than or equal to ±5%, and there is no continuous voltage drop trend.

[0015] Compared with the prior art, the hierarchical black-start method for DC microgrids according to the embodiments of the present invention has the following significant advantages: This invention eliminates the reliance on physical communication links such as CAN and Ethernet for traditional black starts through an autonomous coordination mechanism based on bus voltage characteristics. Each power conversion device can achieve synchronization and coordinated aggregation of "latent signals" by sensing voltage fluctuations and stability characteristics at the point of common coupling (PCC). This design not only eliminates the risk of system-level startup failure due to communication cable faults or electromagnetic interference, but also greatly simplifies system wiring complexity and reduces construction and maintenance costs.

[0016] This invention organically combines "short-circuit detection, collaborative aggregation, and closed-loop voltage regulation" through a three-stage startup process. The first stage utilizes low-voltage detection combined with a sampling compensation algorithm to effectively avoid the impact on power devices during startup with short-circuit faults. The second stage achieves power synergy among multiple devices through coarse-grained control. The third stage ensures output voltage quality by switching to a refined closed-loop mode. This logical progression from coarse to fine ensures a high success rate of black-start process under complex operating conditions.

[0017] The voltage threshold, time window, and load priority involved in this invention all support user-defined configuration. This highly flexible control system can seamlessly adapt to heterogeneous devices such as energy storage converters (ESC), DC charging piles (DCC), and photovoltaic converters, solving the problems of fixed parameters and difficulty in taking into account the dynamic characteristics of multiple types of devices in existing technical solutions, and providing a standardized black-start solution for industrial and commercial microgrids.

[0018] This invention addresses the problem of hardware sampling circuits being susceptible to noise interference during the low-voltage startup phase. It incorporates a sampling error compensation algorithm into the first-stage startup procedure and combines the dual characteristics of "voltage ratio + current surge" to determine short-circuit faults. This improvement significantly enhances the system's ability to distinguish between actual faults and measurement noise, avoiding unnecessary protection shutdowns caused by sampling deviations.

[0019] This invention deeply couples the black start process with load priority management. When startup is hindered, loads are cut off in order of "low to high," and after startup is completed, loads are restored in an orderly manner of "small to large, high to low." This refined load management strategy maximizes the priority restoration of core loads such as communication and scheduling, preventing secondary system collapse caused by high-power load surges.

[0020] This invention also allows maintenance personnel to intuitively understand the current black boot phase of the system through a series of structured status codes output by the status identification module. In the event of an anomaly, the status code can precisely pinpoint which specific program level or type of device is experiencing the problem, significantly improving the maintenance efficiency of off-grid systems. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart of a hierarchical black-start method for DC microgrids according to an embodiment of the present invention; Figure 2 This is a flowchart of a black-start control method for multiple devices without interconnection and collaboration in one embodiment of the present invention; Figure 3 This is a flowchart of a multi-device non-interconnected collaborative black-start control method according to an embodiment of the present invention; Figure 4 This is a graph showing the bus voltage variation in one embodiment of the present invention. Figure 5 This is a system status code change curve diagram according to one embodiment of the present invention; Figure 6 This is a hardware structure diagram of a computing device according to an embodiment of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0024] This invention provides a hierarchical black start method and system for DC microgrids, which solves the technical problems in the prior art where the black start process relies excessively on physical communication links, the start parameters are fixed, and the short circuit detection is easily affected by sampling errors, leading to start-up failure.

[0025] Currently, existing technologies have the following drawbacks in the field of black start for DC microgrids: 1) The collaborative logic is highly dependent on physical communication. Existing solutions typically require synchronizing the start commands of each converter via physical links such as CAN bus or Ethernet. In extreme fault conditions that damage communication cables or cause strong electromagnetic interference, the system cannot achieve multi-device collaboration, making black start difficult to implement.

[0026] 2) The short circuit detection mechanism has a low fault tolerance rate. Traditional short circuit detection does not fully consider the inherent bias error of the sampling circuit and environmental noise. It is very easy to make misjudgments during the low voltage detection stage, which can cause the normally operating system to fail to start due to protection malfunction.

[0027] 3) Insufficient flexibility in parameter configuration. Key parameters such as voltage threshold and time window during startup are mostly fixed settings, making it difficult to adapt to heterogeneous equipment combinations with different power levels and response characteristics (such as a mix of energy storage, photovoltaics, and charging piles).

[0028] 4) The load recovery lacks a systematic strategy. The power restoration process after a black start often lacks priority stratification, which leads to severe voltage drops when high-power loads are connected, causing secondary system crashes.

[0029] To address the aforementioned shortcomings, the present invention aims to address the following: One of the objectives is to achieve autonomous coordination based on bus voltage characteristics, thereby eliminating dependence on physical communication lines.

[0030] The second objective is to improve the accuracy of short-circuit detection and collaborative assembly through a tiered activation and error compensation mechanism.

[0031] The third objective is to provide a parameterized configuration interface to improve the system's adaptability to heterogeneous devices.

[0032] Fourth objective: To establish a scientific load management logic to ensure the stability of black start results and the smoothness of power restoration.

[0033] In summary, this invention achieves autonomous aggregation of multiple devices without the need for communication by using the voltage of the common coupling point (PCC) as an implicit coordination signal through a three-level progressive startup process; at the same time, it constructs a highly reliable and highly compatible black-start control system by combining error compensation and priority load regulation.

[0034] Please see Figures 1-2 This invention provides a hierarchical black-start method for DC microgrids, applicable to DC microgrids containing one or more devices including energy storage converters, DC charging piles, and photovoltaic converters, with each device connected in parallel to a common coupling point (PCC) at the DC bus. The method includes the following steps: The first-level startup step involves controlling the target device to output a configurable first voltage threshold to the common coupling point and continuously monitoring for a preset first duration. If the bus voltage reaches the first voltage threshold and no fault logic is triggered within the first duration, the short circuit detection is deemed successful, and the second-level startup step is initiated. If the bus voltage is continuously lower than a preset percentage of the first voltage threshold, a short circuit or overload power fault is determined, triggering the first fault flag and executing the fault handling procedure. The second-level startup step involves controlling the target device to maintain the bus voltage at or above the first voltage threshold, and waiting for other devices to autonomously start operation within a preset second time period to complete the coordinated assembly by sensing the bus voltage characteristics. At the end of the second time period, if the bus voltage stabilizes above the preset second voltage threshold, the coordinated assembly is determined to be successful, and the third-level startup step is initiated. If the bus voltage drops below the second voltage threshold, the black start is determined to be a failure, and the second fault indicator is triggered. The third-level startup step involves switching the control mode of the target device to closed-loop control, regulating the bus voltage to climb towards a configurable third voltage threshold, and continuously monitoring for a preset third duration. If the bus voltage reaches the third voltage threshold and the fluctuation range is within the allowable range, a startup completion status flag is generated; otherwise, a third fault flag is triggered.

[0035] In a further embodiment, the first-level startup step is used to execute the first-level startup procedure and perform short-circuit detection.

[0036] In this embodiment, the target device (such as an energy storage converter with master control capability) is first controlled to output a configurable first voltage threshold (e.g., 50V) to the PCC point, and the preset first duration is continuously monitored.

[0037] During this stage, the system executes fault logic judgment: when the bus voltage is detected to be continuously lower than 5% to 15% of the first voltage threshold for a first duration, and accompanied by abrupt changes in the output current (such as the current instantaneously reaching the current limit value or the rate of change exceeding the limit), it is determined that there is a physical short circuit in the system.

[0038] At this point, the system invokes its built-in linear error compensation strategy to correct the voltage sampling data, covering a hardware sampling error range of ±0.5% to ±2% to eliminate misjudgments caused by circuit temperature drift or noise. If no error is detected, the first fault flag is triggered and the system shuts down. If a normal voltage build-up is detected, the short-circuit detection is deemed successful, and the system proceeds to the second stage.

[0039] If the voltage still fails to build up after the short circuit is eliminated, the system determines that the load power is over the limit. After disconnecting part of the load in the order of "non-critical load priority, high power load priority", the first-level startup is re-executed.

[0040] In a further embodiment, the second-level startup step is used to execute the second-level startup procedure: to achieve interconnection-free collaborative aggregation.

[0041] The target device maintains the bus voltage at or above the first voltage threshold and waits for other devices (non-target devices) to join within a preset second time period.

[0042] At this time, non-target devices within the microgrid (such as photovoltaic converters or DC charging piles) continuously monitor the voltage status of the PCC point through the autonomous coordination module. When the voltage is detected to be stable above the first voltage threshold for a preset duration, the non-target device autonomously determines that it is currently in the black-start coordination phase and initiates its own pre-charge or discharge program to participate in the bus voltage support.

[0043] The target equipment makes a judgment by monitoring the steady-state maintenance duration and fluctuation characteristics of the bus voltage: if the bus voltage fluctuation amplitude is within the allowable range or stabilizes above the second voltage threshold at the end of the second duration, the coordinated assembly is determined to be successful and enters the third level; otherwise, the second fault indicator is triggered.

[0044] In a further embodiment, the third-level startup step is used to execute the third-level startup procedure and perform closed-loop stable voltage regulation.

[0045] The system switches the control mode of the target device from the initial hysteresis or open-loop control to a high-precision closed-loop control mode.

[0046] The bus voltage is smoothly increased towards a configurable third voltage threshold (i.e., the system's rated operating voltage, such as 750V), and the third duration is continuously monitored. If the bus voltage reaches the preset target and the fluctuation range is within the allowable range, the status indicator module generates a startup completion status indicator (such as status code 5000); otherwise, a third fault indicator is triggered.

[0047] In a further embodiment, the present invention also includes a process for performing load regulation and recovery, which specifically includes: After generating a startup completion flag and running stably for a preset duration, loads that were previously removed are gradually added based on load priority.

[0048] Load connection follows the principle of "prioritizing core system loads, followed by critical social loads, and lastly general loads." After each load level is connected, monitoring for a preset duration must be performed to confirm the absence of voltage dips or current surges before connecting the next load level.

[0049] For heterogeneous devices, this embodiment configures differentiated control strategies: for DC charging piles, low-priority interfaces and high-power charging modules are prioritized to be cut off; for photovoltaic converters, non-essential power output units are prioritized to be cut off; for energy storage converters, non-core energy storage support loads are prioritized to be cut off.

[0050] To verify the technical effectiveness of this implementation, such as Figure 3As shown, in a specific embodiment of the present invention, the energy storage converter (ESC), DC charging pile (DCC), and photovoltaic converter can be arbitrarily combined or connected as a single device. The multi-device non-interconnected collaborative black start refers to the DC microgrid in the figure, that is, the common coupling point PCC of the DC bus terminal of the devices. Through the energy storage converter (ESC), DC charging pile (DCC), and photovoltaic converter, photovoltaic panels, energy storage units, and new energy vehicles and other power-consuming devices can be connected respectively.

[0051] In a further embodiment, such as Figure 4 As shown, during the black start process, the DC microgrid, i.e., the DC bus common coupling point PCC of the equipment, has an output port voltage of the DC bus common coupling point PCC, since the control target is any combination of energy storage converter (ESC), DC charging pile (DCC), and photovoltaic converter or a single device. The waveform shows a three-stage black start process: 140.2s~142s is the first stage; 142s~143.2s is the second stage; and after 143.2s is the third stage. Figure 5 As shown, each state during the black start process has a corresponding definition, including the first-level start, 4329: verify the bus voltage boost capability. If the bus voltage is less than 50V for 0.5s, the system switches to Error. The second-level start has a preset second duration, autonomously identifies the "black start requirement" and starts its own start process, with status codes: 4321MuxDC pre-discharge to boost BUS voltage / 4322BATT pre-discharge to boost BUS voltage / 4323PV pre-discharge to boost BUS voltage. The third-level start switches the system from the original hysteresis control to closed-loop control logic, transforming the coarse control mode into fine control. Through the closed-loop control strategy, the target device will output a configurable DC bus voltage to the output port, the DC bus common coupling point PCC, with status codes: 4340PV boost BUS logic / 4351muxDC discharge to boost BUS voltage / 4352BATT discharge to boost BUS voltage.

[0052] This invention presents a multi-device autonomous collaboration mechanism without physical interconnections. It uses bus voltage as an implicit signal to achieve device aggregation, solving the problem of reliance on communication links in traditional solutions, reducing system complexity and cost, and improving anti-interference capabilities. All voltage thresholds and time parameters in this invention are configurable, allowing users to customize them according to device type (ESC / DCC / PV) and scenario requirements, breaking through the limitations of fixed parameters in traditional solutions and achieving wider adaptability. Furthermore, this invention combines a sampling error compensation algorithm with a dual judgment based on voltage ratio and current surge, avoiding short-circuit misjudgments caused by sampling deviations and improving startup safety. This invention also establishes a shared control system for ESC, DCC, and PV converters, adapting to various device characteristics through differentiated load regulation strategies to achieve system-level black start standardization. This invention also provides a hierarchical black-start system for DC microgrids, such as... Figure 6 As shown, it includes: The control unit stores configurable voltage thresholds and time parameters, and outputs start-up control signals and load regulation signals.

[0053] The voltage and current monitoring module is used to collect PCC point data and perform offline correction of the sampled values ​​using a built-in linear error compensation algorithm.

[0054] The autonomous collaboration module is used to analyze voltage amplitude and fluctuation characteristics, and identify black start requirements and grid connection status of each device in the absence of physical communication cables.

[0055] The load management module receives control signals and performs precise load shedding and sequential load connection.

[0056] The status identification module is used to generate and output process status codes and fault identifiers in real time, providing decision-making basis for maintenance personnel.

[0057] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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.

[0058] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. 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 illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A system that specifies functions in one or more boxes.

[0059] 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 an instruction set implemented in a process. Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0060] 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.

[0061] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A hierarchical black-start method for DC microgrids, applied to a DC microgrid containing one or more devices including energy storage converters, DC charging piles, and photovoltaic converters, wherein each device is connected in parallel to a common coupling point (PCC) at the DC bus terminal, characterized in that, The method does not require establishing physical communication connections between devices. Instead, it achieves autonomous coordination by monitoring the voltage status of a common coupling point, and includes the following steps: The first-level startup step involves controlling the target device to output a configurable first voltage threshold to the common coupling point and continuously monitoring for a preset first duration. If the bus voltage reaches the first voltage threshold and no fault logic is triggered within the first duration, the short circuit detection is deemed successful, and the second-level startup step is initiated. If the bus voltage is continuously lower than a preset percentage of the first voltage threshold, a short circuit or overload power fault is determined, triggering the first fault flag and executing the fault handling procedure. The second-level startup step involves controlling the target device to maintain the bus voltage at or above the first voltage threshold, and waiting for other devices to autonomously start operation within a preset second time period to complete the coordinated assembly by sensing the bus voltage characteristics. At the end of the second time period, if the bus voltage stabilizes above the preset second voltage threshold, the coordinated assembly is determined to be successful, and the third-level startup step is initiated. If the bus voltage drops below the second voltage threshold, the black start is determined to be a failure, and the second fault indicator is triggered. The third-level startup step involves switching the control mode of the target device to closed-loop control, regulating the bus voltage to climb towards a configurable third voltage threshold, and continuously monitoring for a preset third duration. If the bus voltage reaches the third voltage threshold and the fluctuation range is within the allowable range, a startup completion status flag is generated; otherwise, a third fault flag is triggered.

2. The hierarchical black-start method for DC microgrids according to claim 1, characterized in that, The first voltage threshold, the second voltage threshold, and the third voltage threshold are configurable parameters stored in the device control unit; the first duration, the second duration, and the third duration are configurable time parameters set according to the device response characteristics.

3. The hierarchical black-start method for DC microgrids according to claim 1, characterized in that, The fault logic judgment rule in the first-level startup step is as follows: when the bus voltage is continuously lower than 5%-15% of the first voltage threshold within the first time period, and is accompanied by sudden changes in output current, it is determined that there is a short circuit fault in the system; the fault handling process includes: correcting the sampling data by combining the preset voltage sampling error compensation value, and triggering the equipment protection mechanism after confirming the short circuit; if the voltage is still not established after the short circuit is eliminated, it is determined that the load power is over-limit, and the load is disconnected in the order of non-critical load priority and high power load priority, and the first-level startup step is re-executed.

4. The hierarchical black-start method for DC microgrids according to claim 1, characterized in that, The autonomous coordination mechanism in the second-level startup step is as follows: non-target devices in the microgrid monitor the voltage at the common coupling point. When the voltage is found to be stable above the first voltage threshold, they autonomously determine the black start requirement and initiate their own pre-charge or discharge program to participate in the bus voltage support. Target devices determine whether multiple devices in the system have completed coordinated aggregation by detecting the steady-state maintenance duration and voltage fluctuation characteristics of the bus voltage.

5. The hierarchical black-start method for DC microgrids according to claim 1, characterized in that, After generating the startup completion status flag, the load recovery process is also included: After the system has been running stably for a preset period of time, loads that were previously removed will be gradually connected based on load priority and device power parameters. The load access sequence follows the principle of "prioritizing core system loads, followed by critical social loads, and lastly general loads." After each load is accessed, voltage and current monitoring is performed for a preset observation period to confirm that there are no abnormal fluctuations before the next level of load is accessed.

6. The hierarchical black-start method for DC microgrids according to claim 5, characterized in that, Configure differentiated load control strategies for different equipment types: For DC charging piles, prioritize disconnecting low-priority charging interfaces and high-power charging modules. For photovoltaic converters, prioritize cutting off non-essential power output units; For energy storage converters, non-core energy storage support loads should be cut off first.

7. A hierarchical black-start system for a DC microgrid, characterized in that, include: The control unit is configured to execute the control method according to any one of claims 1 to 6, store configurable voltage thresholds and time parameters, and output a start control signal and a load regulation signal; The voltage and current monitoring module is configured to collect DC bus voltage and output current data, and then correct the data by combining the built-in sampling error compensation algorithm before feeding it back to the control unit; The autonomous collaboration module is configured to identify the system's black start requirements and the grid connection status of other devices by analyzing the amplitude and fluctuation characteristics of the bus voltage, and to achieve multi-device collaboration under the condition of no physical interconnection communication cables. The load management module is configured to receive control signals from the control unit and perform load disconnection and connection operations; The status identification module is configured to generate and output status codes and fault indicators during the startup process.

8. The system according to claim 7, characterized in that, The voltage and current monitoring module has a built-in linear error compensation strategy to correct the collected voltage signal offline, with a compensation range covering sampling errors of ±0.5% to ±2%.

9. The system according to claim 7, characterized in that, The conditions for the autonomous collaboration module to determine the completion of multi-device collaborative aggregation include: within the second time period, the bus voltage fluctuation amplitude is less than or equal to ±5%, and there is no continuous voltage drop trend.

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