Parallel-serial type network configuration energy storage control method and system for improving microgrid black start

Abstract

The application discloses a series-parallel type network construction energy storage control method and system for improving black start of a microgrid, and relates to the technical field of distributed control. In the method, microgrid line impedance data and voltage and current response signals of series and parallel branch energy storage units after injection of a sweep excitation are acquired; frequency response characteristic curves of series branch impedance and parallel branch admittance are respectively calculated according to the response signals; phase margin spectra of the series and parallel branches are calculated in combination with the line impedance data; the minimum phase margin is extracted to determine a resonance risk type and a dangerous frequency; an impedance compensation strategy is executed on the energy storage units according to the above, and compensated impedance configurations are obtained; and finally, a hierarchical start sequence is generated based on the configurations, and the microgrid is controlled to complete black start. The technical solution provided by the application can improve the accuracy of microgrid black start in a complex impedance matching scenario.

Description

Technical Field

[0001] This invention belongs to the field of distributed control technology, specifically a series-parallel grid-connected energy storage control method and system for improving black start of microgrids. Background Technology

[0002] With the rapid development of distributed energy resources and the increasing demands for power supply reliability in power systems, microgrids have been widely adopted as a flexible form of power supply. Microgrids operate in both stand-alone and grid-connected modes. When the main grid experiences a fault or planned power outage, the microgrid needs black-start capability, meaning it can autonomously start and restore power supply without external power support, relying on its own energy storage system or distributed power sources. To adapt to the diverse application scenarios with different capacity levels, topologies, and load characteristics, the control architecture of energy storage systems is showing a diversified development trend. Its stability and reliability in complex grid environments are crucial for ensuring the success rate of the black-start process.

[0003] Currently, energy storage control methods during microgrid black start primarily rely on preset control parameters. These parameters are used by a grid-connected inverter to simulate voltage source characteristics, providing voltage and frequency support to the system and completing the start-up task. This black start method based on fixed control parameters can achieve basic start-up functions under conditions of sufficient energy storage capacity and simple system structure, and has been widely used in the field of microgrid black start.

[0004] However, due to the complexity of grid impedance characteristics and the diversity of energy storage output characteristics, black start scenarios are becoming increasingly complex and variable. In practical applications, black start methods based on fixed control parameters struggle to suppress the interference of factors such as impedance mismatch on system stability, and the reliability of the startup process is difficult to guarantee. Especially when the output impedance of the energy storage unit interacts with the grid line impedance at certain frequency points, the system may experience impedance mismatch across multiple frequency ranges. These unfavorable impedance interactions superimpose or couple, and existing methods employing uniform control strategies are prone to causing oscillations or even resonant instability during startup, thus reducing the accuracy of microgrid black start under complex impedance matching scenarios. Summary of the Invention

[0005] To address the above problems, this invention provides a series-parallel grid-connected energy storage control method and system for improving black start of microgrids. This method solves the problem that existing black start methods are prone to resonant instability under complex impedance matching scenarios, and can improve the accuracy of black start of microgrids under complex impedance matching scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The system acquires the grid line impedance data of the microgrid, as well as the voltage response and current response signals of the series branch energy storage unit and the parallel branch energy storage unit after the injection of the frequency sweep excitation signal. The output impedance of the series branch energy storage unit is in series with the grid line impedance in the equivalent circuit, and the output characteristics of the parallel branch energy storage unit are in parallel with the grid line impedance in the equivalent circuit. Based on the voltage response signal and the current response signal, the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch are calculated respectively. Based on the power grid line impedance data, the impedance frequency response characteristic curve of the series branch, and the admittance frequency response characteristic curve of the parallel branch, the phase margin spectrum of the series branch and the phase margin spectrum of the parallel branch are calculated respectively. Extract the series minimum phase margin of the phase margin spectrum of the series branch and the parallel minimum phase margin of the phase margin spectrum of the parallel branch, and determine the resonance risk type and the corresponding danger frequency based on the series minimum phase margin and the parallel minimum phase margin. Based on the resonance risk type and the dangerous frequency, corresponding impedance compensation strategies are executed on the series branch energy storage unit and the parallel branch energy storage unit to obtain the compensated impedance configuration. A graded start-up sequence is generated based on the compensated impedance configuration, and the microgrid is controlled to complete a black start according to the graded start-up sequence. The determination of the resonance risk type and corresponding danger frequency based on the series minimum phase margin and the parallel minimum phase margin includes: The series minimum phase margin and the parallel minimum phase margin are compared with preset phase margin safety thresholds, respectively. If the series minimum phase margin is lower than the preset phase margin safety threshold and the parallel minimum phase margin is not lower than the preset phase margin safety threshold, then the resonance risk type is determined to be series-dominant resonance risk, and the frequency corresponding to the series minimum phase margin is determined to be the dangerous frequency. If the minimum phase margin in parallel is lower than the preset phase margin safety threshold and the minimum phase margin in series is not lower than the preset phase margin safety threshold, then the resonance risk type is determined to be parallel-dominant resonance risk, and the frequency corresponding to the minimum phase margin in parallel is determined to be the dangerous frequency. If both the series minimum phase margin and the parallel minimum phase margin are lower than the preset phase margin safety threshold, then the resonance risk type is determined to be coupled resonance risk, and the frequency corresponding to the series minimum phase margin is taken as the series dangerous frequency, the frequency corresponding to the parallel minimum phase margin is taken as the parallel dangerous frequency, and the series dangerous frequency and the parallel dangerous frequency together constitute the dangerous frequency.

[0007] By employing the aforementioned technical solution, and by acquiring the grid line impedance data of the microgrid and the response signals of the series-parallel branch energy storage units after the injection of a frequency sweep excitation signal, a comprehensive understanding of the system's impedance characteristics was obtained. Based on the response signals, the impedance-frequency response characteristic curves of the series branches and the admittance-frequency response characteristic curves of the parallel branches were calculated, achieving accurate characterization of the energy storage unit's output characteristics. Furthermore, the phase margin spectrum of the series-parallel branches was calculated, transforming the complex impedance matching problem into a quantifiable and assessable phase margin index. By extracting the minimum phase margin of the series-parallel branch phase margin spectrum, the weakest stability link in the system and its critical frequency were accurately identified, enabling early prediction of potential resonance risks. For the identified resonance risk types and critical frequencies, corresponding impedance compensation strategies were implemented for the series-parallel branch energy storage units. This overcomes the limitations of existing methods that use a uniform control strategy, implementing differentiated compensation for different types of impedance interaction problems, effectively suppressing the superposition or coupling effects of unfavorable impedance interactions across multiple frequency ranges. Finally, a graded start-up sequence was generated based on the compensated impedance configuration, and the microgrid was controlled to complete the black start. This ensured that the system maintained a good impedance matching state throughout the start-up process, avoiding oscillations and resonance instability caused by impedance mismatch, and improving the accuracy of microgrid black start in complex impedance matching scenarios.

[0008] Optionally, at each frequency point, the impedance magnitude and impedance phase angle are calculated according to the ratio of the voltage response signal to the current response signal, and the impedance magnitude and impedance phase angle are mapped to the impedance frequency response characteristic curve of the series branch; at each frequency point, the admittance magnitude and admittance phase angle are calculated according to the ratio of the current response signal to the voltage response signal, and the admittance magnitude and admittance phase angle are mapped to the admittance frequency response characteristic curve of the parallel branch.

[0009] Optionally, the ratio of the impedance corresponding to the impedance frequency response characteristic curve of the series branch to the impedance data of the power grid line is used as the first open-loop transfer function. The first phase margin of the first open-loop transfer function at each frequency point is calculated, and the distribution sequence of the first phase margins corresponding to each frequency point is used as the phase margin spectrum of the series branch. The product of the admittance corresponding to the admittance frequency response characteristic curve of the parallel branch and the impedance data of the power grid line is used as the second open-loop transfer function. The second phase margin of the second open-loop transfer function at each frequency point is calculated, and the distribution sequence of the second phase margins corresponding to each frequency point is used as the phase margin spectrum of the parallel branch.

[0010] Optionally, if the resonance risk type is series-dominant resonance risk, the virtual impedance is reconstructed by introducing an additional virtual damping term into the control loop of the series branch energy storage unit until the phase margin of the series branch energy storage unit at the corresponding dangerous frequency is not lower than a preset phase margin safety threshold, thus obtaining the compensated impedance configuration; if the resonance risk type is parallel-dominant resonance risk, the droop coefficient is reconstructed by introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit until the phase margin of the parallel branch energy storage unit at the corresponding dangerous frequency is not lower than a preset phase margin safety threshold, thus obtaining the compensated impedance configuration.

[0011] Optionally, if the resonance risk type is coupled resonance risk, the virtual impedance of the series branch energy storage unit is reconstructed by injecting virtual reactance compensation, and the corresponding series dangerous frequency is shifted to a position where the difference between the series dangerous frequency and the parallel dangerous frequency is not less than a preset safe frequency interval, thus obtaining the impedance configuration after series frequency shift; based on the impedance configuration after series frequency shift, the impedance frequency response characteristic curve of the series branch is updated, and the decoupled parallel phase margin is recalculated; the droop coefficient is reconstructed by introducing a transient droop compensation term in the power control loop of the parallel branch energy storage unit until the decoupled parallel phase margin is not lower than a preset phase margin safe threshold at the corresponding parallel dangerous frequency, thus obtaining the compensated impedance configuration.

[0012] Optionally, using the compensated impedance configuration as the current configuration, the frequency sweep excitation signal is injected, and the compensated series branch phase margin spectrum and the compensated parallel branch phase margin spectrum are calculated. It is verified whether all phase margins in the compensated series branch phase margin spectrum and the compensated parallel branch phase margin spectrum are not lower than the preset phase margin safety threshold. If the verification fails, the impedance adjustment step size is reduced by a preset shrinkage ratio, and the steps of executing the corresponding impedance compensation strategy for the series branch energy storage unit and the parallel branch energy storage unit are returned based on the reduced impedance adjustment step size until the verification passes. The impedance configuration when the verification passes is determined as the compensated impedance configuration.

[0013] Optionally, based on the compensated impedance configuration, calculate the maximum safe output boundary of each energy storage unit; obtain the candidate set of energy storage units to be included in the startup sequence and the set of energy storage units already included in the startup sequence; for each candidate unit in the candidate set, calculate the combined impedance phase margin spectrum corresponding to its inclusion in the set of energy storage units, and extract the minimum phase margin in each combined impedance phase margin spectrum; determine the candidate unit corresponding to the maximum value in the minimum phase margin as the startup unit of this stage, and calculate the target value of the bus voltage after the startup of this stage is completed based on the combined impedance configuration after the startup unit of this stage is included; The current-level start-up unit is added to the energy storage unit set. When the total capacity of the energy storage unit set is less than the preset target load capacity threshold, the current-level start-up unit is removed from the energy storage unit candidate set to update the energy storage unit candidate set. Then, the process returns to the step of calculating the combined impedance phase margin spectrum corresponding to each candidate unit in the energy storage unit candidate set after adding it to the energy storage unit set. When the total capacity of the energy storage unit set is not less than the target load capacity threshold, the recorded start-up units at each level and the corresponding bus voltage establishment target values ​​are combined according to the start-up order to generate the hierarchical start-up sequence.

[0014] Optionally, each stage of startup is executed sequentially according to the tiered startup sequence, and the measured value of the bus voltage is collected after each stage startup is completed; the deviation amplitude between the measured value of the bus voltage and the target value of the corresponding bus voltage for this stage is calculated; if the deviation amplitude exceeds a preset deviation range, the impedance configuration parameters of the next stage corresponding energy storage unit are corrected proportionally according to the deviation direction and magnitude of the deviation amplitude; based on the corrected impedance configuration parameters, the next stage startup is initiated until the deviation amplitude between the measured value of the final stage bus voltage and the target value of the corresponding bus voltage does not exceed the preset deviation range, and the black startup is confirmed to be completed.

[0015] Secondly, embodiments of this application provide a series-parallel grid-connected energy storage control system for improving microgrid black start. This system includes one or more processors and a memory. The memory is coupled to the one or more processors and stores computer program code, including computer instructions. The one or more processors invoke the computer instructions to cause the system to perform the method described in the first aspect and any possible implementation thereof.

[0016] In summary, one or more technical solutions provided in this application have at least the following technical effects or advantages: By employing the aforementioned technical solution, and by acquiring the grid line impedance data of the microgrid and the response signals of the series-parallel branch energy storage units after the injection of a frequency sweep excitation signal, a comprehensive understanding of the system's impedance characteristics was obtained. Based on the response signals, the impedance-frequency response characteristic curves of the series branches and the admittance-frequency response characteristic curves of the parallel branches were calculated, achieving accurate characterization of the energy storage unit's output characteristics. Furthermore, the phase margin spectrum of the series-parallel branches was calculated, transforming the complex impedance matching problem into a quantifiable and assessable phase margin index. By extracting the minimum phase margin of the series-parallel branch phase margin spectrum, the weakest stability link in the system and its critical frequency were accurately identified, enabling early prediction of potential resonance risks. For the identified resonance risk types and critical frequencies, corresponding impedance compensation strategies were implemented for the series-parallel branch energy storage units. This overcomes the limitations of existing methods that use a uniform control strategy, implementing differentiated compensation for different types of impedance interaction problems, effectively suppressing the superposition or coupling effects of unfavorable impedance interactions across multiple frequency ranges. Finally, a graded start-up sequence was generated based on the compensated impedance configuration and the microgrid was controlled to complete the black start. This ensured that the system maintained a good impedance matching state throughout the start-up process, avoiding oscillations and resonance instability caused by impedance mismatch, and improving the accuracy of microgrid black start in complex impedance matching scenarios. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a series-parallel grid-connected energy storage control method for improving black start of microgrids, as disclosed in an embodiment of this application. Figure 2 This is another schematic flowchart of a series-parallel grid-connected energy storage control method for improving black start of microgrids disclosed in an embodiment of this application; Figure 3 This is a schematic diagram of the structure of a system provided in an embodiment of this application.

[0018] In the diagram: 301, Central Processing Unit; 302, Read-Only Memory; 303, Random Access Memory; 304, Bus; 305, Input / Output Interface; 306, Input Section; 307, Output Section; 308, Storage Section; 309, Communication Section; 310, Driver; 311, Removable Media. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solution, the present invention will be described in detail below with reference to embodiments. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0020] It should be noted that, in this document, the terms "comprising," "including," and any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Specific examples have been used in this document to illustrate the principles and implementation methods of the present invention. These examples are merely for the purpose of helping to understand the method and core ideas of the present invention. The above are only preferred embodiments of the present invention. It should be pointed out that, due to the limitations of written expression and the objective existence of infinite specific structures, those skilled in the art can make several improvements, modifications, or variations without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, variations, or combinations, or the direct application of the concept and technical solution of the present invention to other situations without modification, should all be considered within the scope of protection of the present invention.

[0021] This application provides a series-parallel grid-connected energy storage control method to improve black start performance in microgrids, referring to... Figure 1 , Figure 1 This is a flowchart illustrating a series-parallel grid-connected energy storage control method for improving black start of microgrids, provided in an embodiment of this application. The method is applied to a system, which refers to a hardware and software integrated platform capable of executing a series-parallel grid-connected energy storage control program for improving black start of microgrids. The system can execute a series-parallel grid-connected energy storage control program for improving black start of microgrids. The method includes steps 101 to 106, as follows: Step 101: Obtain the grid line impedance data of the microgrid, as well as the voltage response signal and current response signal of the series branch energy storage unit and the parallel branch energy storage unit after the injection of the frequency sweep excitation signal. The output impedance of the series branch energy storage unit is in series with the grid line impedance in the equivalent circuit, and the output characteristics of the parallel branch energy storage unit are in parallel with the grid line impedance in the equivalent circuit.

[0022] In this embodiment, a microgrid refers to a combined system of power sources, loads, and energy storage devices capable of autonomous control, protection, and management, with both grid-connected and off-grid operating modes. Grid line impedance data refers to the impedance parameters of the internal lines of the microgrid, including components such as resistance, inductance, and capacitance, used to characterize the grid lines' impediment to current transmission. A series branch energy storage unit refers to an energy storage device connected to the grid in series, typically an energy storage converter connected via an LC filter. A parallel branch energy storage unit refers to an energy storage device connected to the grid in parallel, generally an energy storage converter directly connected in parallel. A swept-frequency excitation signal represents an electrical signal that varies with time within a certain frequency range, used to excite the system to obtain the system's response characteristics at different frequencies. A voltage response signal refers to the voltage change signal generated by the system under the action of the swept-frequency excitation signal. A current response signal represents the current change signal generated by the system under the action of the swept-frequency excitation signal.

[0023] Specifically, firstly, the impedance data of the microgrid's power lines is acquired through a system parameter measurement device or a pre-stored database. This data includes the distribution of line impedance values ​​at different frequencies. Then, a sweep frequency excitation signal is injected into the series branch energy storage units in the microgrid system. The signal frequency gradually increases from the starting frequency to the ending frequency according to a preset step size. The voltage and current response signals of the series branch energy storage units at each frequency point are collected by the measurement device, and the collected data is digitized and stored. Similarly, a sweep frequency excitation signal with the same parameters is injected into the parallel branch energy storage units, and the corresponding voltage and current response signals are collected. To improve measurement accuracy, the collected signals can be filtered to eliminate noise interference, and the sampling frequency must meet the requirements of the Nyquist sampling theorem to avoid signal aliasing.

[0024] It should be noted that in this application, "series branch" and "parallel branch" are classifications of the equivalent output characteristics of energy storage units based on impedance modeling, rather than the physical series or parallel connection of the DC-side electrical connection of the energy storage units. Specifically, the series branch energy storage unit is connected to the grid line via passive components such as LC filters, and its output impedance is in series with the grid line impedance in the equivalent circuit, exhibiting the Thevenin equivalent characteristics of a voltage source series impedance. The parallel branch energy storage unit is directly connected in parallel to the microgrid bus, and its output characteristics are in parallel with the grid line impedance in the equivalent circuit, exhibiting the Norton equivalent characteristics of a current source parallel admittance. At the physical connection level, both series branch energy storage units and parallel branch energy storage units can be connected to the microgrid in parallel via the bus to achieve capacity expansion and redundancy configuration. The distinction between the two does not affect their actual access topology in the microgrid.

[0025] It should be noted that, in order to avoid unexpected resonance caused by injecting a frequency sweep excitation signal when the system stability margin is insufficient in the early stage of black start, the frequency sweep excitation signal is injected after the existing single energy storage unit has independently established the initial bus voltage in a small capacity, voltage control mode and is operating stably, rather than directly injecting it in a completely de-energized state before the bus voltage has been established. The amplitude of the frequency sweep excitation signal is controlled within a small signal disturbance range that does not affect the stable operation of the system, and a segmented frequency increase method is used for gradual scanning. During the injection of each frequency band, the bus voltage fluctuation amplitude is monitored in real time. If the voltage fluctuation exceeds the preset safety range, the signal injection of the current frequency band is immediately stopped and the subsequent injection amplitude is reduced, thereby ensuring the safety of the system operation in the early stage of black start while obtaining system impedance characteristic data.

[0026] Step 102: Based on the voltage response signal and the current response signal, calculate the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch, respectively.

[0027] In this embodiment, the impedance frequency response curve represents the curve of impedance changing with frequency, including data in two dimensions: impedance magnitude and phase angle. The admittance frequency response curve represents the curve of admittance changing with frequency; admittance is the reciprocal of impedance, and also includes data in two dimensions: admittance magnitude and phase angle.

[0028] Specifically, for series-connected energy storage units, the impedance values ​​at each frequency point are calculated using the acquired voltage and current response signals. First, for each test frequency point, the amplitude of the voltage response signal at that frequency is divided by the amplitude of the current response signal to obtain the impedance magnitude at that frequency; simultaneously, the difference between the phase of the voltage response signal and the phase of the current response signal is calculated to obtain the impedance phase angle at that frequency. The impedance magnitudes and phase angles of all test frequency points are arranged in frequency order to form the impedance-frequency response characteristic curve of the series branch. For parallel-connected energy storage units, a similar method is used, but admittance is calculated instead of impedance. Specifically, for each test frequency point, the amplitude of the current response signal at that frequency is divided by the amplitude of the voltage response signal to obtain the admittance magnitude at that frequency; simultaneously, the difference between the phase of the current response signal and the phase of the voltage response signal is calculated to obtain the admittance phase angle at that frequency. The admittance magnitudes and phase angles of all test frequency points are arranged in frequency order to form the admittance-frequency response characteristic curve of the parallel branch.

[0029] In one possible implementation, the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch are calculated based on the voltage response signal and the current response signal, respectively. Specifically, this includes steps 1021-1022, as follows: Step 1021: Calculate the impedance magnitude and impedance phase angle at each frequency point according to the ratio of the voltage response signal to the current response signal, and map the impedance magnitude and impedance phase angle to the impedance frequency response characteristic curve of the series branch.

[0030] Specifically, the process begins by extracting information for each frequency point from the acquired voltage and current response signal data. For each test frequency point, the effective values ​​and phase information of the voltage and current response signals at that frequency are extracted. Then, the impedance magnitude at each frequency point is calculated, which is the effective value of the voltage response signal divided by the effective value of the current response signal. Simultaneously, the impedance phase angle at each frequency point is calculated, which is the difference between the phase of the voltage response signal and the phase of the current response signal. Next, the impedance magnitude and phase angle data for all frequency points are arranged in ascending order of frequency, forming impedance magnitude-frequency data pairs and impedance phase angle-frequency data pairs. Finally, these data pairs are plotted on a frequency coordinate system, with the horizontal axis representing frequency and the vertical axis representing impedance magnitude and impedance phase angle, respectively, thus forming the impedance-frequency response characteristic curve of the series branch. To improve the smoothness and continuity of the curve, interpolation algorithms can be used between discrete measurement frequency points to generate a more continuous curve. Commonly used interpolation methods include linear interpolation and spline interpolation.

[0031] Step 1022: Calculate the admittance magnitude and admittance phase angle at each frequency point according to the ratio of the current response signal to the voltage response signal, and map the admittance magnitude and admittance phase angle to the admittance frequency response characteristic curve of the parallel branch.

[0032] Specifically, the process begins by extracting information for each frequency point from the acquired voltage and current response signal data. For each test frequency point, the effective values ​​and phase information of the current and voltage response signals at that frequency are extracted. Then, the admittance magnitude at each frequency point is calculated by dividing the effective value of the current response signal by the effective value of the voltage response signal. Simultaneously, the admittance phase angle at each frequency point is calculated, which is the difference between the phase of the current response signal and the phase of the voltage response signal. Next, the admittance magnitude and phase angle data for all frequency points are arranged in ascending order of frequency, forming admittance magnitude-frequency data pairs and admittance phase angle-frequency data pairs. Finally, these data pairs are plotted on a frequency coordinate system, with the horizontal axis representing frequency and the vertical axis representing the admittance magnitude and admittance phase angle, respectively, thus forming the admittance frequency response characteristic curve of the parallel branch. To make the curve more continuous and easier to analyze, interpolation can be performed on the values ​​between discrete measurement frequency points to obtain a smoother admittance frequency response characteristic curve. Commonly used interpolation methods include linear interpolation, polynomial interpolation, and Fourier transform-based interpolation methods.

[0033] Step 103: Based on the power grid line impedance data, the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch, calculate the phase margin spectrum of the series branch and the phase margin spectrum of the parallel branch respectively.

[0034] In the embodiments of this application, the phase margin spectrum represents the phase margin distribution of the system at different frequency points. The phase margin is an important indicator for evaluating the stability of the system, representing the difference between the phase when the system gain is 1 and -180 degrees.

[0035] Specifically, for series branches, the impedance values ​​in the obtained impedance-frequency response characteristic curve of the series branch are compared with the grid line impedance data to construct an open-loop transfer function. For each frequency point, the phase margin of the open-loop transfer function is calculated, which is the difference between the phase when the gain is 1 and -180 degrees. If the gain of the open-loop transfer function at a certain frequency point is not 1, the phase needs to be interpolated to obtain the phase value when the gain of the function is 1, and then the difference with -180 degrees is calculated. The phase margin values ​​of all frequency points are arranged in frequency order to form the phase margin spectrum of the series branch. For parallel branches, a similar method is used, but when constructing the open-loop transfer function, the product relationship between the admittance value in the admittance-frequency response characteristic curve of the parallel branch and the grid line impedance data is used. Similarly, for each frequency point, the phase margin of the open-loop transfer function is calculated, and the phase margin values ​​of all frequency points are arranged in frequency order to form the phase margin spectrum of the parallel branch.

[0036] In one possible implementation, based on the power grid line impedance data, the impedance frequency response characteristic curve of the series branch, and the admittance frequency response characteristic curve of the parallel branch, the phase margin spectrum of the series branch and the phase margin spectrum of the parallel branch are calculated respectively, specifically including steps 1031-1032, as follows: Step 1031: Take the ratio of the impedance corresponding to the impedance frequency response characteristic curve of the series branch to the impedance data of the power grid line as the first open-loop transfer function, calculate the first phase margin of the first open-loop transfer function at each frequency point, and take the distribution series of the first phase margins corresponding to each frequency point as the phase margin spectrum of the series branch.

[0037] Specifically, firstly, the impedance frequency response characteristic curve data of the series branch is obtained, which includes the impedance magnitude and phase angle information at different frequency points. Simultaneously, the power grid line impedance data is obtained, including the impedance characteristics of the power grid at each frequency point. Then, for each frequency point, the ratio of the series branch impedance to the power grid line impedance is calculated to obtain the frequency response characteristic of the first open-loop transfer function. When calculating the ratio, the magnitude and phase angle need to be processed separately. The ratio of magnitudes is equal to the series branch impedance magnitude divided by the power grid line impedance magnitude, and the difference in phase angles is equal to the series branch impedance phase angle minus the power grid line impedance phase angle. Next, for each frequency point, the phase margin of the first open-loop transfer function is calculated. The specific calculation method is as follows: First, find the frequency point where the magnitude of the first open-loop transfer function is equal to 1. If this point is not among the existing frequency points, the phase angle of this point is determined by interpolation. Then, the difference between the phase angle of this point and the critical phase angle is calculated to obtain the phase margin. For all frequency points, the above calculation process is repeated to obtain the first phase margin value corresponding to each frequency point. Finally, all frequency points and their corresponding first phase margin values ​​are arranged in frequency order to form a distribution series, namely the series branch phase margin spectrum. To improve calculation accuracy, the sampling density can be increased near key frequency points to ensure that the changing trend of the phase margin can be accurately captured.

[0038] Step 1032: Take the product of the admittance corresponding to the admittance frequency response characteristic curve of the parallel branch and the power grid line impedance data as the second open-loop transfer function, calculate the second phase margin of the second open-loop transfer function at each frequency point, and take the distribution series of the second phase margins corresponding to each frequency point as the phase margin spectrum of the parallel branch.

[0039] Specifically, firstly, the admittance frequency response characteristic curve data of the parallel branch is obtained. This curve includes the admittance magnitude and phase angle information at different frequency points. Simultaneously, the grid line impedance data is obtained, including the grid impedance characteristics at each frequency point. Then, for each frequency point, the product of the parallel branch admittance and the grid line impedance is calculated to obtain the frequency response characteristic of the second open-loop transfer function. When calculating the product, the magnitude and phase angle need to be processed separately. The product of the magnitudes equals the parallel branch admittance magnitude multiplied by the grid line impedance magnitude, and the sum of the phase angles equals the parallel branch admittance phase angle plus the grid line impedance phase angle. Next, for each frequency point, the phase margin of the second open-loop transfer function is calculated. The specific calculation method is as follows: First, find the frequency point where the second open-loop transfer function magnitude equals 1. If this point is not among the existing frequency points, the phase angle of this point is determined by interpolation. Then, the difference between the phase angle of this point and the critical phase angle is calculated to obtain the phase margin. For all frequency points, the above calculation process is repeated to obtain the second phase margin value corresponding to each frequency point. Finally, all frequency points and their corresponding second phase margin values ​​are arranged in frequency order to form a distribution sequence, namely the parallel branch phase margin spectrum. To ensure the accuracy of the critical frequency band, an adaptive frequency sampling method can be used to increase the sampling density in areas with large phase margin variations.

[0040] Step 104: Extract the series minimum phase margin of the phase margin spectrum of the series branch and the parallel minimum phase margin of the phase margin spectrum of the parallel branch, and determine the resonance risk type and the corresponding danger frequency based on the series minimum phase margin and the parallel minimum phase margin.

[0041] In this embodiment, the series minimum phase margin represents the minimum value in the phase margin spectrum of the series branch, and is a key indicator for measuring the stability margin of the series branch. The parallel minimum phase margin represents the minimum value in the phase margin spectrum of the parallel branch, and is a key indicator for measuring the stability margin of the parallel branch. Resonance risk type refers to the classification of resonance risks that the system may face, including series-dominant resonance risk, parallel-dominant resonance risk, and coupled resonance risk. The danger frequency refers to the frequency point at which the system may resonate, at which the system's stability is worst.

[0042] Specifically, first, the minimum value is found in the calculated series branch phase margin spectrum; this minimum value is the series minimum phase margin, and the corresponding frequency point is recorded. Similarly, the minimum value is found in the parallel branch phase margin spectrum; this minimum value is the parallel minimum phase margin, and the corresponding frequency point is recorded. Then, the series and parallel minimum phase margins are compared with pre-set safety thresholds. If the series minimum phase margin is lower than the safety threshold while the parallel minimum phase margin is not lower than the safety threshold, the system is determined to face a series-dominant resonance risk, and the danger frequency is the frequency point corresponding to the series minimum phase margin. If the parallel minimum phase margin is lower than the safety threshold while the series minimum phase margin is not lower than the safety threshold, the system is determined to face a parallel-dominant resonance risk, and the danger frequency is the frequency point corresponding to the parallel minimum phase margin. If both the series and parallel minimum phase margins are lower than the safety threshold, the system is determined to face a coupled resonance risk, and the danger frequencies include the frequencies corresponding to both the series and parallel minimum phase margins.

[0043] In one possible implementation, the resonance risk type and corresponding danger frequency are determined based on the series minimum phase margin and the parallel minimum phase margin, specifically including steps 1041-1043, as follows: Step 1041: Compare the series minimum phase margin and the parallel minimum phase margin with the preset phase margin safety threshold respectively; if the series minimum phase margin is lower than the preset phase margin safety threshold and the parallel minimum phase margin is not lower than the preset phase margin safety threshold, then determine the resonance risk type as series-dominant resonance risk, and determine the frequency corresponding to the series minimum phase margin as the dangerous frequency.

[0044] Specifically, the first step is to acquire the phase margin spectra of the series and parallel branches. The minimum value in the series branch phase margin spectrum is identified and used as the minimum series phase margin, with the corresponding frequency point recorded. Similarly, the minimum value in the parallel branch phase margin spectrum is identified and used as the minimum parallel phase margin, with the corresponding frequency point recorded. Then, a preset phase margin safety threshold is set. This threshold is typically determined based on system stability requirements and engineering experience, and is generally set to around 30 degrees. Next, the minimum series phase margin is compared with the preset phase margin safety threshold, and the minimum parallel phase margin is also compared with the preset phase margin safety threshold. If the minimum series phase margin is found to be less than the preset phase margin safety threshold, while the minimum parallel phase margin is greater than or equal to the preset phase margin safety threshold, the system is determined to face a risk of series-dominant resonance. In this case, the frequency point corresponding to the minimum series phase margin is identified as the system's critical frequency, which requires close monitoring and handling. Information on the type of resonance risk and the dangerous frequency is stored for use in the formulation of impedance compensation strategies in subsequent steps.

[0045] Step 1042: If the minimum phase margin in parallel is lower than the preset phase margin safety threshold and the minimum phase margin in series is not lower than the preset phase margin safety threshold, then the resonance risk type is determined to be parallel-dominant resonance risk, and the frequency corresponding to the minimum phase margin in parallel is determined to be the dangerous frequency.

[0046] Specifically, the first step involves using the acquired series and parallel minimum phase margin data, along with their corresponding frequency information. The parallel minimum phase margin is compared to a preset phase margin safety threshold, and the series minimum phase margin is also compared to the preset phase margin safety threshold. If the parallel minimum phase margin is found to be less than the preset phase margin safety threshold, while the series minimum phase margin is greater than or equal to the preset phase margin safety threshold, the system is determined to face a parallel-dominant resonance risk. In this case, the frequency point corresponding to the parallel minimum phase margin is identified as the system's critical frequency, requiring focused attention and handling. This judgment is based on the characteristic that the parallel branch has poor stability at this frequency point, while the series branch is relatively stable. The determined resonance risk type and critical frequency information are recorded; this information will be used in subsequent steps to develop targeted impedance compensation strategies. In practical applications, accurate identification of the critical frequency is crucial for effectively suppressing resonance risks; therefore, a more refined frequency scan may be necessary near the critical frequency point to more accurately determine the system's critical frequency.

[0047] Step 1043: If both the series minimum phase margin and the parallel minimum phase margin are lower than the preset phase margin safety threshold, then the resonance risk type is determined to be coupled resonance risk, and the frequency corresponding to the series minimum phase margin is taken as the series dangerous frequency, and the frequency corresponding to the parallel minimum phase margin is taken as the parallel dangerous frequency. The series dangerous frequency and the parallel dangerous frequency together constitute the dangerous frequency.

[0048] Specifically, the first step involves using the acquired series and parallel minimum phase margin data, along with their corresponding frequency information. The series minimum phase margin is compared to a preset phase margin safety threshold, and the parallel minimum phase margin is also compared to the preset phase margin safety threshold. If both the series and parallel minimum phase margins are found to be less than the preset phase margin safety threshold, the system is deemed to face a coupled resonance risk. In this case, the dangerous frequency points for both series and parallel connections need to be identified separately. The frequency point corresponding to the series minimum phase margin is designated as the series dangerous frequency, and the frequency point corresponding to the parallel minimum phase margin is designated as the parallel dangerous frequency. These two frequency points together constitute the system's dangerous frequency set. The identified resonance risk type and dangerous frequency set information are recorded; this information will be used in subsequent steps to develop more complex impedance compensation strategies. Because coupled resonance risk involves stability issues at multiple frequency points, handling this risk typically requires a more comprehensive compensation method, which may include techniques such as frequency decoupling and multi-frequency compensation. In practical applications, it is also necessary to analyze the relationship between series dangerous frequencies and parallel dangerous frequencies, such as frequency spacing and phase margin differences, in order to formulate more effective compensation strategies.

[0049] Step 105: Based on the resonance risk type and the dangerous frequency, perform the corresponding impedance compensation strategy on the series branch energy storage unit and the parallel branch energy storage unit to obtain the compensated impedance configuration.

[0050] In this application embodiment, the impedance compensation strategy refers to the impedance adjustment method adopted for different types of resonance risks, used to improve the stability of the system at dangerous frequencies. The compensated impedance configuration refers to the impedance parameter setting of the energy storage unit after adjustment by the impedance compensation strategy.

[0051] Specifically, different impedance compensation strategies are adopted based on the determined resonance risk type. If the resonance risk type is series-dominated, the output impedance characteristics are adjusted by adding a virtual damping term to the control loop of the series branch energy storage unit. In practice, a feedback term proportional to the rate of change of output current can be introduced into the voltage control loop of the energy storage unit; this proportionality coefficient is the virtual damping coefficient. By gradually increasing the virtual damping coefficient, the phase margin of the series branch energy storage unit at the dangerous frequency reaches or exceeds a preset safety threshold, resulting in the compensated impedance configuration. If the resonance risk type is parallel-dominated, the output impedance characteristics are adjusted by introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit. In practice, a compensation term proportional to the rate of change of power can be added to the power control loop; this proportionality coefficient is the transient droop coefficient. By gradually adjusting the transient droop coefficient, the phase margin of the parallel branch energy storage unit at the dangerous frequency reaches or exceeds a preset safety threshold, resulting in the compensated impedance configuration. If the resonance risk type is coupled resonance risk, it is necessary to first inject virtual reactance compensation into the series branch energy storage unit to move the series dangerous frequency to a position with a sufficient frequency interval from the parallel dangerous frequency to achieve frequency decoupling. Then, transient droop compensation is performed on the parallel branch to obtain the final compensated impedance configuration.

[0052] In one possible implementation, based on the resonance risk type and the dangerous frequency, corresponding impedance compensation strategies are performed on the series branch energy storage units and the parallel branch energy storage units to obtain the compensated impedance configuration. Specifically, this includes steps 1051-1052, as follows: Step 1051: If the resonance risk type is series-dominant resonance risk, then the virtual impedance is reconstructed by introducing an additional virtual damping term into the control loop of the series branch energy storage unit until the phase margin of the series branch energy storage unit at the corresponding dangerous frequency is not lower than the preset phase margin safety threshold, and the compensated impedance configuration is obtained.

[0053] Specifically, firstly, based on the determined series-dominant resonance risk and corresponding danger frequency, the original control parameters and impedance characteristics of the series branch energy storage unit at that danger frequency are extracted. Then, a virtual damping control module is designed and implemented, capable of generating a compensation signal proportional to the rate of change of current. This virtual damping control module is integrated into the existing voltage control loop of the series branch energy storage unit to form an improved control structure. Initially, the virtual damping coefficient is set to a small value, and then gradually increased. For each virtual damping coefficient value, the new impedance characteristics of the series branch energy storage unit at the danger frequency are remeasured or calculated, and the corresponding phase margin is calculated using grid line impedance data. The calculated phase margin is compared with a preset phase margin safety threshold. If the current phase margin is still below the safety threshold, the virtual damping coefficient is increased further, and the above measurement and calculation process is repeated. When the phase margin first reaches or exceeds the preset safety threshold, the current virtual damping coefficient and the corresponding control parameter settings are recorded. Finally, these parameter configurations are applied to the control system of the series branch energy storage unit to complete the reconstruction of the virtual impedance and obtain the compensated impedance configuration. To ensure the stability of the compensation effect, the phase margin after compensation can be verified near multiple frequency points to ensure that there are no new resonance risk points throughout the frequency range.

[0054] Step 1052: If the resonance risk type is parallel-dominant resonance risk, the droop coefficient is reconstructed by introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit until the phase margin of the parallel branch energy storage unit at the corresponding dangerous frequency is not lower than the preset phase margin safety threshold, and the compensated impedance configuration is obtained.

[0055] Specifically, firstly, based on the determined parallel dominant resonance risk and corresponding danger frequency, the original control parameters and admittance characteristics of the parallel branch energy storage unit at that danger frequency are extracted. Then, a transient droop control module is designed and implemented, capable of generating a compensation signal proportional to the power change rate. This transient droop control module is integrated into the existing power control loop of the parallel branch energy storage unit, forming an improved control structure. Initially, the transient droop coefficient is set to a small value, and then gradually increased. For each transient droop coefficient value, the new admittance characteristics of the parallel branch energy storage unit at the danger frequency are remeasured or calculated, and the corresponding phase margin is calculated using grid line impedance data. The calculated phase margin is compared with a preset phase margin safety threshold. If the current phase margin is still below the safety threshold, the transient droop coefficient is increased further, and the above measurement and calculation process is repeated. When the phase margin first reaches or exceeds the preset safety threshold, the current transient droop coefficient and the corresponding control parameter settings are recorded. Finally, these parameter configurations are applied to the control system of the parallel branch energy storage unit to reconstruct the droop coefficient and obtain the compensated impedance configuration. To ensure the comprehensiveness of the compensation effect, the performance of the compensated system can be verified under different operating conditions to ensure good stability under various operating conditions.

[0056] In one possible implementation, based on the resonance risk type and the dangerous frequency, corresponding impedance compensation strategies are performed on the series branch energy storage units and the parallel branch energy storage units to obtain the compensated impedance configuration. This further includes steps 1053-1055, as follows: Step 1053: If the resonance risk type is coupled resonance risk, the virtual impedance of the series branch energy storage unit is reconstructed by injecting virtual reactance compensation, and the corresponding series dangerous frequency is shifted to a position that differs from the parallel dangerous frequency by no less than the preset safe frequency interval, so as to obtain the impedance configuration after series frequency shift.

[0057] Specifically, firstly, based on the determined coupled resonance risk type and the corresponding series and parallel dangerous frequencies, the interval between the two dangerous frequencies is calculated. Simultaneously, a preset safe frequency interval is set based on system characteristics; this interval should be large enough to ensure that the two resonance types do not interfere with each other. Then, it is determined whether the current frequency interval is less than the preset safe frequency interval. If it is, a frequency shift operation is required. The direction and magnitude of the frequency shift are determined, typically shifting the series dangerous frequency away from the parallel dangerous frequency. A virtual reactance compensation module is designed and implemented, which can generate an equivalent reactance effect in the control system of the series branch energy storage unit. A small initial virtual reactance compensation amount is set, which can be positive (equivalent inductance) or negative (equivalent capacitance), depending on the required frequency shift direction. This virtual reactance compensation amount is injected into the control loop of the series branch energy storage unit. The impedance-frequency response characteristic curve of the modified series branch is remeasured or calculated, and the new series dangerous frequency is extracted from it. The interval between the new series dangerous frequency and the original parallel dangerous frequency is calculated and compared with the preset safe frequency interval. If the frequency interval is still less than the preset safe frequency interval, increase the magnitude of the virtual reactance compensation and repeat the above process. When the interval between two frequencies reaches or exceeds the preset safe frequency interval for the first time, record the current virtual reactance compensation and the corresponding control parameter settings to obtain the impedance configuration after series frequency shift.

[0058] Step 1054: Based on the impedance configuration after series frequency shift, update the impedance frequency response characteristic curve of the series branch and recalculate the decoupled parallel phase margin.

[0059] Specifically, firstly, based on the obtained impedance configuration after series frequency shift, the impedance frequency response characteristic curve of the series branch is remeasured or calculated. This process can be completed through theoretical calculation or actual testing. In theoretical calculation, the injected virtual reactance compensation needs to be incorporated into the mathematical model of the series branch energy storage unit, a new impedance expression is derived, and the impedance value is calculated at each frequency point. If the actual testing method is used, the control parameters of the virtual reactance compensation need to be applied to the series branch energy storage unit first, and then the measurement is repeated according to step 102 to obtain the updated impedance frequency response characteristic curve. Next, combining the updated impedance frequency response characteristic curve of the series branch and the grid line impedance data, the open-loop transfer function of the parallel branch is recalculated. Specifically, for each frequency point, the product of the parallel branch admittance and the grid line impedance is calculated, while considering the impact of the updated series branch impedance on the grid characteristics. Based on the new open-loop transfer function, the phase margin at each frequency point is calculated according to step 103, forming the decoupled parallel phase margin spectrum. Special attention is paid to the phase margin value at the dangerous parallel frequency points to evaluate the decoupling effect. The decoupled parallel phase margin is compared with the preset phase margin safety threshold. If it is still lower than the safety threshold, further compensation processing is required in subsequent steps.

[0060] Step 1055: Reconstruct the droop coefficient by introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit until the decoupled parallel phase margin is not lower than the preset phase margin safety threshold at the corresponding parallel dangerous frequency, and obtain the compensated impedance configuration.

[0061] Specifically, firstly, based on the calculated decoupled parallel phase margin, it is confirmed whether the phase margin value at the parallel critical frequency point meets the safety requirements. If the value is still lower than the preset phase margin safety threshold, transient droop compensation is required. A transient droop compensation module is designed and implemented, which can generate a compensation signal proportional to the power change rate. This transient droop compensation module is integrated into the power control loop of the parallel branch energy storage unit to form an improved control structure. Initially, the transient droop coefficient is set to a small value, and then the coefficient is gradually increased. For each transient droop coefficient value, the admittance frequency response characteristic curve of the parallel branch energy storage unit is recalculated, especially the admittance characteristic at the parallel critical frequency point. Based on the updated admittance characteristic and grid line impedance data, the phase margin at the parallel critical frequency point is calculated according to the method in step 103. The calculated phase margin is compared with the preset phase margin safety threshold. If it is still lower than the safety threshold, the transient droop coefficient is increased further, and the above calculation process is repeated. When the phase margin first reaches or exceeds the preset safety threshold, the current transient droop coefficient and the corresponding control parameter settings are recorded. Finally, the obtained impedance configuration after series frequency shift is combined with the current control parameter settings of the parallel branch to form the compensated impedance configuration of the system. This configuration includes virtual reactance compensation for the series branch and transient droop compensation for the parallel branch, which can effectively address the risk of coupled resonance.

[0062] In one possible implementation, after obtaining the compensated impedance configuration, steps 1056-1057 are further included, as follows: Step 1056: Using the compensated impedance configuration as the current configuration, inject a sweep frequency excitation signal and calculate the compensated phase margin spectrum of the series branch and the compensated phase margin spectrum of the parallel branch.

[0063] Specifically, the obtained compensated impedance configuration is first applied to the system, including parameters such as the virtual reactance compensation of the series branch energy storage unit and the transient droop coefficient of the parallel branch energy storage unit. In actual operation, these parameters need to be converted into specific parameter values ​​in the controller and written into the corresponding controller. Then, a frequency sweep excitation signal is prepared, which should cover the entire frequency range where the system may have resonance risks. The start frequency, end frequency, sweep rate, and signal amplitude of the frequency sweep are determined according to the system characteristics. The signal amplitude should be kept within a range that does not affect the normal operation of the system, typically 0.5% to 5% of the rated value. The prepared frequency sweep excitation signal is injected into the system, which can be done at control points such as voltage reference value, current reference value, or power reference value. During the frequency sweep, the system's input signal and output response are recorded simultaneously. For series branches, the voltage or current signal and its response at the injection point are recorded; for parallel branches, the corresponding input and output signal pairs are also recorded. Based on the recorded input and output signals, the impedance characteristics at different frequency points are calculated. For each frequency point, the amplitude ratio and phase difference between the output signal and the input signal are calculated to form the frequency response characteristics of the system. Using the acquired frequency response characteristics, the phase margin of the system at each frequency point is calculated. For series branches, the phase margin of the open-loop transfer function is calculated based on their impedance characteristics and grid parameters; for parallel branches, the corresponding phase margin is calculated similarly based on their admittance characteristics and grid parameters. The phase margin values ​​at all frequency points are sorted by frequency to form the compensated phase margin spectrum of the series branches and the compensated phase margin spectrum of the parallel branches. These two phase margin spectra will be used in the next step to verify the compensation effect.

[0064] Step 1057: Verify whether all phase margins in the compensated series branch phase margin spectrum and the compensated parallel branch phase margin spectrum are not lower than the preset phase margin safety threshold; if the verification fails, reduce the impedance adjustment step size by the preset shrinkage ratio, and return to the step of executing the corresponding impedance compensation strategy for the series branch energy storage unit and the parallel branch energy storage unit based on the reduced impedance adjustment step size, until the verification passes, and determine the impedance configuration when the verification passes as the compensated impedance configuration.

[0065] Specifically, first, all phase margin values ​​in the obtained compensated series branch phase margin spectrum and compensated parallel branch phase margin spectrum are checked. The phase margin values ​​corresponding to all frequency points are extracted from both phase margin spectra to form a complete phase margin dataset. A preset phase margin safety threshold is used as the judgment criterion; this threshold is typically determined based on system stability requirements and engineering safety margins. All phase margin values ​​are compared with the preset phase margin safety threshold to check for any phase margin values ​​below the safety threshold. If all phase margin values ​​are not lower than the preset phase margin safety threshold, the verification is considered successful, and the current impedance configuration meets system stability requirements. If the phase margin at any frequency point is lower than the safety threshold, the verification is considered unsuccessful, and further impedance configuration adjustments are required. In the case of unsuccessful verification, the current impedance adjustment step size is first determined, including the adjustment step size for the virtual reactance compensation of the series branch and the adjustment step size for the transient droop coefficient of the parallel branch. Then, the impedance adjustment step size is reduced according to a preset shrinkage ratio, which is typically less than 1, such as 0.5 or 0.8. The specific calculation method involves multiplying the current impedance adjustment step size by a preset shrinkage ratio to obtain the reduced impedance adjustment step size. Using this reduced step size, the impedance compensation strategy for both series and parallel branch energy storage units is re-executed, i.e., steps 1053 to 1056 are returned to the execution process. During this return execution, using a smaller adjustment step size allows for finer impedance parameter adjustments, thereby more accurately optimizing the system phase margin. The impedance compensation and verification loop is repeated until the phase margin at all frequency points is not lower than the preset safety threshold, indicating successful verification. When verification is successful, the current impedance configuration is determined as the final compensated impedance configuration. This configuration will guide the actual setting of system parameters to ensure stable system operation.

[0066] Step 106: Generate a graded start-up sequence based on the compensated impedance configuration, and control the microgrid to complete the black start according to the graded start-up sequence.

[0067] In this embodiment, the tiered startup sequence refers to a plan that determines the startup of each energy storage unit according to a specific order and parameters, including the startup order and the corresponding voltage establishment target value. Black start refers to the process by which a microgrid system, without external power support, achieves a transition from a complete power outage state to normal operation through its own energy storage devices.

[0068] Specifically, firstly, based on the obtained compensated impedance configuration, the maximum safe output boundary of each energy storage unit is calculated, i.e., the maximum power that each energy storage unit can provide under the premise of ensuring system stability. Then, a candidate set of energy storage units and a set of energy storage units already included in the startup sequence are established. Initially, the candidate set contains all available energy storage units, and the included set is empty. For each energy storage unit in the candidate set, the combined impedance characteristics after adding it to the included set are calculated, and the corresponding phase margin spectrum is evaluated, extracting the minimum phase margin value. The energy storage unit that maximizes the minimum phase margin is selected as the startup unit for this stage and moved from the candidate set to the included set. Based on the updated included set, the target value for bus voltage establishment after the startup of this stage is calculated. The above steps are repeated until the total capacity of the included set reaches the preset target load capacity threshold. Finally, the startup units determined at each stage and the corresponding target values ​​for bus voltage establishment are combined according to the startup sequence to form a complete hierarchical startup sequence. During the actual black start process, each energy storage unit is sequentially controlled to start operation according to this hierarchical startup sequence, and the deviation between the actual value and the target value of the bus voltage is monitored after each stage of startup is completed. If the deviation exceeds the preset range, the parameters of the next-level start-up unit will be corrected according to the direction and magnitude of the deviation.

[0069] In one possible implementation, the microgrid is controlled to complete a black start according to a hierarchical start sequence, specifically including steps 1061-1063, as follows: Step 1061: Execute each stage of the startup sequence in sequence, and collect the measured value of the bus voltage after each stage is completed; calculate the deviation amplitude between the measured value of the bus voltage and the target value of the bus voltage corresponding to this stage.

[0070] Specifically, the energy storage units and their startup order for each stage are first determined according to a pre-set tiered startup sequence. For the first stage startup, the corresponding energy storage units are started according to the set control mode and parameters, typically using a voltage control mode to establish the initial bus voltage. After startup, real-time bus voltage data is collected using voltage sensors to obtain the measured bus voltage value. Simultaneously, the target bus voltage establishment value corresponding to the current stage is extracted from the tiered startup sequence. This target value is the voltage level that the system expects to reach after the completion of this stage startup. The difference between the measured bus voltage value and the target bus voltage establishment value is calculated to obtain the deviation amplitude. This calculation process involves subtracting the target value from the measured value, and the result includes both the magnitude and the positive or negative direction. For each stage startup after the first stage, the above process is repeated: the energy storage unit corresponding to the current stage is started, and after it stabilizes, the measured bus voltage value is collected, and the deviation amplitude from the target value is calculated. Throughout the entire process, a preset time interval is maintained between each stage startup to ensure that the system has sufficient time to reach a steady state, thereby obtaining accurate deviation assessment results.

[0071] Step 1062: If the deviation amplitude exceeds the preset deviation range, the impedance configuration parameters of the next-level energy storage unit are corrected proportionally according to the deviation direction and magnitude.

[0072] Specifically, the first step is to compare the calculated deviation amplitude with the preset deviation range. The preset deviation range is the upper and lower limits of the voltage deviation allowed by the system, usually expressed as a percentage of the nominal value, such as ±5%. Next, it's determined whether the deviation amplitude exceeds the preset deviation range, i.e., whether the absolute value of the deviation amplitude is greater than the threshold of the preset deviation range. If the deviation amplitude is within the preset range, no correction is needed, and the system proceeds directly to the next stage of startup. If the deviation amplitude exceeds the preset range, impedance parameter correction is required. The direction of the deviation is then determined, i.e., whether the measured value is higher or lower than the target value. If the measured value is higher than the target value, the deviation direction is positive; if the measured value is lower than the target value, the deviation direction is negative. Based on the deviation direction and amplitude, the correction amount for the impedance configuration parameters is calculated. The correction amount is proportional to the deviation amplitude; that is, the larger the deviation, the larger the correction amount. A linear proportional relationship can be used in the calculation, multiplying the deviation amplitude by a preset correction coefficient to obtain the parameter adjustment amount. An appropriate correction method is selected based on the deviation direction: if the measured voltage is too high, the output impedance of the next-stage energy storage unit is increased; if the measured voltage is too low, the output impedance of the next-stage energy storage unit is decreased. The calculated corrections are applied to the impedance configuration parameters of the next-stage energy storage unit to obtain the corrected impedance parameter values. These corrected parameters will be used during the startup process of the next-stage energy storage unit to compensate for voltage deviations after the current stage starts up.

[0073] Step 1063: Based on the corrected impedance configuration parameters, proceed to the next stage of startup until the deviation between the measured value of the final bus voltage and the corresponding target value of the bus voltage does not exceed the preset deviation range, and confirm that the black start is complete.

[0074] Specifically, the control system of the next-level energy storage unit is first configured using the corrected impedance configuration parameters. These corrected parameters include virtual impedance parameters and controller gain, used to adjust the output characteristics of the energy storage unit. Following the prescribed sequence of the tiered startup sequence, the next-level energy storage unit is started, integrating it into the system with the established initial voltage. After the next-level energy storage unit stabilizes, the measured bus voltage value is collected again to obtain the current system voltage status. The target value for establishing the bus voltage corresponding to the current level is extracted from the tiered startup sequence as an evaluation standard. The deviation amplitude between the measured bus voltage value of the current level and the corresponding target value is calculated, using the same method as step 1061. It is determined whether the calculated deviation amplitude exceeds the preset deviation range. If the deviation amplitude exceeds the preset range, the process returns to step 1062 to correct the impedance configuration parameters of the next-level energy storage unit. If the deviation amplitude is within the preset range, it is determined whether this is the final stage startup. If it is not the final stage, the next stage startup continues; if it is the final stage, it indicates that all levels of energy storage units have successfully started and the voltage has reached the target requirement. When the deviation between the measured value of the final bus voltage and the corresponding target value of the bus voltage does not exceed the preset deviation range, the black start process is confirmed to be successfully completed, the system has established a stable bus voltage, and loads or other power generation units can be connected.

[0075] In the above embodiments, dynamic compensation control during the microgrid black start process is achieved through real-time voltage monitoring and impedance parameter adjustment during the graded start-up process. To further improve system stability and safety margin during the black start process and realize intelligent planning of the optimal start-up sequence of energy storage units, this application also provides a series-parallel grid-connected energy storage control method to improve microgrid black start. This method analyzes the impedance characteristic interaction between energy storage units and its impact on system stability, constructs an energy storage unit start-up sequence optimization mechanism based on the principle of maximizing phase margin, and performs precise calculation of the target value for bus voltage establishment. This enables the system to scientifically and rationally arrange the start-up sequence of each energy storage unit while ensuring maximum stability margin, effectively preventing resonance, oscillation, or even instability that may occur during the coordinated black start-up of multiple energy storage units. The following is a combination of... Figure 2 The following describes the series-parallel grid-connected energy storage control method for improving black start of microgrids in the embodiments of this application: Please see Figure 2 This is another schematic diagram of a series-parallel grid-connected energy storage control method for improving black start of microgrids in an embodiment of this application.

[0076] Step 201: Based on the compensated impedance configuration, calculate the maximum safe output boundary of each energy storage unit.

[0077] Specifically, the first step is to obtain the compensated impedance configuration data for each energy storage unit. This data includes key information such as the unit's impedance parameters and frequency characteristics. For each unit, the relationship between its compensated impedance characteristics and system stability is analyzed, establishing a mapping relationship between power output and stability margin. Based on the unit's rated capacity, dynamic response characteristics, and impedance characteristics, the maximum power output limit that the unit can provide, i.e., the maximum safe output boundary, is calculated while ensuring system stability. The calculation process needs to consider the impact of the unit's voltage and current limitations, as well as its impedance characteristics, on system stability. System stability analysis methods, such as small-signal stability analysis, are typically used to determine the maximum allowable output power of the energy storage unit while ensuring sufficient system stability margin. The calculation results are recorded as the maximum safe output boundaries for each energy storage unit; these boundary values ​​will serve as constraints for subsequent startup sequence design.

[0078] Step 202: Obtain the candidate set of energy storage units to be included in the startup sequence and the set of energy storage units already included in the startup sequence; for each candidate unit in the candidate set of energy storage units, calculate the combined impedance phase margin spectrum corresponding to the addition to the set of energy storage units, and extract the minimum phase margin in each combined impedance phase margin spectrum.

[0079] Specifically, firstly, a candidate set of all energy storage units that could potentially be included in the startup sequence is obtained. These candidates include all energy storage units in the system that can be used for black start. Simultaneously, a set of energy storage units already determined for inclusion in the startup sequence is obtained; initially, this set may be empty or contain a pre-determined first-stage startup unit. For each candidate unit in the energy storage unit candidate set, the combined impedance phase margin distribution of the entire system within the frequency range of interest is calculated after it is added to the existing energy storage unit set. The calculation requires considering the impedance characteristics of each energy storage unit and analyzing the equivalent impedance characteristics of multiple energy storage units operating in parallel. From a specific minimum frequency to the maximum frequency, with an appropriate frequency step size, the combined impedance phase margin at different frequency points is calculated, forming a complete combined impedance phase margin spectrum. From the combined impedance phase margin spectrum corresponding to each candidate unit, its minimum phase margin value is identified. This minimum value usually appears near the system's characteristic frequency or resonant frequency, representing the weakest link in the system's stability under this combined scheme. The minimum phase margin value corresponding to each candidate unit is recorded as an important indicator for evaluating its impact on system stability after being added to the system.

[0080] Step 203: Determine the candidate unit corresponding to the maximum value in the minimum phase margin as the startup unit of this stage, and calculate the target value of the bus voltage after the startup of this stage is completed based on the combined impedance configuration after adding the startup unit of this stage.

[0081] Specifically, the minimum phase margin values ​​corresponding to each candidate unit are compared, and the largest value is selected. This maximum value represents the optimal system stability among all candidate schemes. The candidate unit corresponding to this maximum value is determined as the startup unit for the current level, i.e., the current-level startup unit. This current-level startup unit is added to the existing energy storage unit set to form a new combination. Based on the updated energy storage unit combination, the new combined impedance configuration of the system is calculated, including considering the parallel effects and interactions of all selected energy storage units. According to the new combined impedance configuration and the total capacity of the currently selected energy storage units, the bus voltage level that the system should reach after the current-level startup is completed is calculated, i.e., the target value for bus voltage establishment. The calculation process needs to consider the relationship between the capacity of the energy storage units and the voltage control capability, as well as the voltage constraints for stable system operation. The current-level startup unit and the corresponding target value for bus voltage establishment are recorded to prepare for the final generation of a complete hierarchical startup sequence.

[0082] Step 204: Add the current-level start-up unit to the energy storage unit set. When the total capacity of the energy storage unit set is less than the preset target load capacity threshold, remove the current-level start-up unit from the energy storage unit candidate set to update the energy storage unit candidate set, and return to execute the step of calculating the combined impedance phase margin spectrum corresponding to each candidate unit in the energy storage unit candidate set after adding it to the energy storage unit set.

[0083] Specifically, the selected startup unit is added to the set of energy storage units already included in the startup sequence, expanding the energy storage unit set. The total capacity of the updated energy storage unit set is calculated, which is the sum of the capacities of all selected energy storage units. The calculated total capacity is compared with a pre-set target load capacity threshold to determine whether the system capacity requirement is met. If the total capacity of the energy storage unit set is less than the target load capacity threshold, it indicates that the capacity of the currently selected energy storage unit set is insufficient to support the target load, and more energy storage units need to be added. At this time, the startup unit is removed from the energy storage unit candidate set to avoid reconsidering the selected units in subsequent selections. The updated energy storage unit candidate set will not contain the selected energy storage units. Return to step 202, and for each candidate unit in the updated energy storage unit candidate set, recalculate its combined impedance phase margin spectrum after being added to the current energy storage unit set, and extract the minimum phase margin value. This iterative process will continue until the condition that the total capacity of the energy storage unit set is not less than the target load capacity threshold is met, or the energy storage unit candidate set is empty and no more units can be added.

[0084] In a preferred embodiment, before each cycle begins, it is first determined whether the energy storage unit candidate set is empty. If the energy storage unit candidate set is empty and the total capacity of the energy storage unit set is still less than the preset target load capacity threshold, it is determined that the currently available energy storage resources are insufficient to support the target load. At this time, the target value of the starting units at each level and their corresponding bus voltages in the energy storage unit set is recorded, and the hierarchical starting sequence is marked as a capacity-limited sequence. At the same time, a capacity shortage prompt message is generated, which includes the difference between the total capacity reached and the target load capacity threshold, so that the operation and maintenance personnel can assess whether it is necessary to temporarily reduce the target load capacity threshold or call other backup energy storage resources. The system performs a black start according to the capacity-limited sequence, restoring only the portion of the load that matches the established capacity.

[0085] If the candidate set of energy storage units is not empty, the combined impedance phase margin spectrum and the corresponding minimum phase margin are calculated for each candidate unit after it is added to the energy storage unit set. It is then determined whether the minimum phase margin of all candidate units is lower than the preset phase margin safety threshold. If they are all lower than the safety threshold, it is determined that adding any candidate unit to the current set of energy storage units will introduce resonance risk exceeding the safety margin. At this time, the selection of the current level of start-up units is stopped, and the target value combination of the determined start-up units at each level and the corresponding bus voltage is established to generate a resonance-limited sequence. At the same time, resonance risk warning information is generated, which includes the candidate unit identifier that causes the risk and its corresponding minimum phase margin value, so that the operation and maintenance personnel can determine whether it is necessary to perform separate impedance compensation on these candidate units in advance before re-including them in the candidate set for subsequent selection. The system performs black start according to the resonance-limited sequence. Candidate units that are not included are transferred to the manual confirmation process. After compensation processing, the generation process of the graded start-up sequence can be triggered again.

[0086] Step 205: When the total capacity of the energy storage unit set is not less than the target load capacity threshold, the recorded start-up units at each level and the corresponding bus voltage are combined according to the start-up order to generate a graded start-up sequence.

[0087] Specifically, when the total capacity of the energy storage unit set reaches or exceeds the preset target load capacity threshold, it indicates that the selected energy storage units are sufficient to support the system's target load, and the tiered start-up unit selection process can end. Information on each level of start-up units recorded during the iterative process is collected, including the identifier, technical parameters, and corresponding target bus voltage establishment value for each level. This information is arranged in order of selection, from the first level to the last, forming a complete start-up unit sequence and voltage target value sequence. Combining this information, structured tiered start-up sequence data is generated, containing necessary information such as the energy storage unit identifier, start-up sequence number, corresponding target bus voltage establishment value, and impedance configuration parameters for each level. The generated tiered start-up sequence is stored in the system as a control guide for subsequent black-start operations. The generation of the tiered start-up sequence marks the completion of the black-start planning phase. The system can then perform actual black-start operations based on this sequence, starting each energy storage unit level by level according to the predetermined order and target, gradually establishing the system voltage, and ultimately achieving complete system power restoration.

[0088] The following describes, from a hardware processing perspective, a series-parallel grid-connected energy storage control system for improving black start of microgrids, according to an embodiment of this invention. Please refer to [link / reference needed]. Figure 3 This is a schematic diagram of a series-parallel grid-connected energy storage control system for improving black start of microgrids in an embodiment of this application.

[0089] It should be noted that, Figure 3 The structure of a series-parallel grid-connected energy storage control system for improving black start of microgrids shown is merely an example and should not impose any limitations on the functionality and scope of application of the embodiments of the present invention.

[0090] like Figure 3 As shown, a series-parallel grid-connected energy storage control system for improving black start of microgrids includes a central processing unit (CPU) 301, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 302 or a program loaded from a storage section 308 into a random access memory (RAM) 303, such as executing the method described in the above embodiment. The RAM 303 also stores various programs and data required for system operation. The CPU 301, ROM 302, and RAM 303 are interconnected via a bus 304. An input / output (I / O) interface 305 is also connected to the bus 304.

[0091] The following components are connected to the input / output interface 305: an input section 306 including audio input devices, push-button switches, etc.; an output section 307 including a liquid crystal display (LCD) and audio output devices, indicator lights, etc.; a storage section 308 including a hard disk, etc.; and a communication section 309 including a network interface card such as a LAN (Local Area Network) card, modem, etc. The communication section 309 performs communication processing via a network such as the Internet. A drive 310 is also connected to the input / output interface 305 as needed. A removable medium 311, such as a disk, optical disk, magneto-optical disk, semiconductor memory, etc., is installed on the drive 310 as needed so that computer programs read from it can be installed into the storage section 308 as needed.

[0092] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present invention. Each block in a flowchart or block diagram may represent a module, program segment, or portion of code, which contains one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those shown in the drawings.

Claims

1. A series-parallel grid-connected energy storage control method for improving black start of microgrids, characterized in that, The method includes: The system acquires the grid line impedance data of the microgrid, as well as the voltage response and current response signals of the series branch energy storage unit and the parallel branch energy storage unit after the injection of the frequency sweep excitation signal. The output impedance of the series branch energy storage unit is in series with the grid line impedance in the equivalent circuit, and the output characteristics of the parallel branch energy storage unit are in parallel with the grid line impedance in the equivalent circuit. Based on the voltage response signal and the current response signal, the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch are calculated respectively. Based on the power grid line impedance data, the impedance frequency response characteristic curve of the series branch, and the admittance frequency response characteristic curve of the parallel branch, the phase margin spectrum of the series branch and the phase margin spectrum of the parallel branch are calculated respectively. Extract the series minimum phase margin of the phase margin spectrum of the series branch and the parallel minimum phase margin of the phase margin spectrum of the parallel branch, and determine the resonance risk type and the corresponding danger frequency based on the series minimum phase margin and the parallel minimum phase margin. Based on the resonance risk type and the dangerous frequency, corresponding impedance compensation strategies are executed on the series branch energy storage unit and the parallel branch energy storage unit to obtain the compensated impedance configuration. A graded start-up sequence is generated based on the compensated impedance configuration, and the microgrid is controlled to complete a black start according to the graded start-up sequence. The determination of the resonance risk type and corresponding danger frequency based on the series minimum phase margin and the parallel minimum phase margin includes: The series minimum phase margin and the parallel minimum phase margin are compared with preset phase margin safety thresholds, respectively. If the series minimum phase margin is lower than the preset phase margin safety threshold and the parallel minimum phase margin is not lower than the preset phase margin safety threshold, then the resonance risk type is determined to be series-dominant resonance risk, and the frequency corresponding to the series minimum phase margin is determined to be the dangerous frequency. If the minimum phase margin in parallel is lower than the preset phase margin safety threshold and the minimum phase margin in series is not lower than the preset phase margin safety threshold, then the resonance risk type is determined to be parallel-dominant resonance risk, and the frequency corresponding to the minimum phase margin in parallel is determined to be the dangerous frequency. If both the series minimum phase margin and the parallel minimum phase margin are lower than the preset phase margin safety threshold, then the resonance risk type is determined to be coupled resonance risk, and the frequency corresponding to the series minimum phase margin is taken as the series dangerous frequency, the frequency corresponding to the parallel minimum phase margin is taken as the parallel dangerous frequency, and the series dangerous frequency and the parallel dangerous frequency together constitute the dangerous frequency.

2. The method according to claim 1, characterized in that, The step of calculating the impedance frequency response characteristic curve of the series branch and the admittance frequency response characteristic curve of the parallel branch based on the voltage response signal and the current response signal, respectively, includes: At each frequency point, the impedance magnitude and impedance phase angle are calculated according to the ratio of the voltage response signal to the current response signal, and the impedance magnitude and impedance phase angle are mapped to the impedance frequency response characteristic curve of the series branch. At each frequency point, the admittance magnitude and admittance phase angle are calculated according to the ratio of the current response signal to the voltage response signal, and the admittance magnitude and admittance phase angle are mapped to the admittance frequency response characteristic curve of the parallel branch.

3. The method according to claim 1, characterized in that, The calculation of the phase margin spectrum of the series branch and the phase margin spectrum of the parallel branch, based on the power grid line impedance data, the impedance frequency response characteristic curve of the series branch, and the admittance frequency response characteristic curve of the parallel branch, includes: The ratio of the impedance corresponding to the impedance frequency response characteristic curve of the series branch to the impedance data of the power grid line is used as the first open-loop transfer function. The first phase margin of the first open-loop transfer function at each frequency point is calculated, and the distribution series of the first phase margins corresponding to each frequency point is used as the phase margin spectrum of the series branch. The product of the admittance corresponding to the admittance frequency response characteristic curve of the parallel branch and the impedance data of the power grid line is used as the second open-loop transfer function. The second phase margin of the second open-loop transfer function at each frequency point is calculated, and the distribution series of the second phase margins corresponding to each frequency point is used as the phase margin spectrum of the parallel branch.

4. The method according to claim 1, characterized in that, The step of performing corresponding impedance compensation strategies on the series branch energy storage unit and the parallel branch energy storage unit based on the resonance risk type and the dangerous frequency to obtain the compensated impedance configuration includes: If the resonance risk type is series-dominant resonance risk, then the virtual impedance is reconstructed by introducing an additional virtual damping term into the control loop of the series branch energy storage unit until the phase margin of the series branch energy storage unit at the corresponding dangerous frequency is not lower than the preset phase margin safety threshold, and the compensated impedance configuration is obtained. If the resonance risk type is parallel-dominant resonance risk, the droop coefficient is reconstructed by introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit until the phase margin of the parallel branch energy storage unit at the corresponding dangerous frequency is not lower than the preset phase margin safety threshold, thus obtaining the compensated impedance configuration.

5. The method according to claim 1, characterized in that, The step of performing corresponding impedance compensation strategies on the series branch energy storage unit and the parallel branch energy storage unit based on the resonance risk type and the dangerous frequency to obtain the compensated impedance configuration further includes: If the resonance risk type is coupled resonance risk, then the virtual impedance of the series branch energy storage unit is reconstructed by injecting virtual reactance compensation, and the corresponding series dangerous frequency is shifted to a position that differs from the parallel dangerous frequency by no less than a preset safe frequency interval, so as to obtain the impedance configuration after series frequency shift. Based on the impedance configuration after the series frequency shift, update the impedance frequency response characteristic curve of the series branch and recalculate the decoupled parallel phase margin. By introducing a transient droop compensation term into the power control loop of the parallel branch energy storage unit to reconstruct the droop coefficient until the decoupled parallel phase margin is not lower than the preset phase margin safety threshold at the corresponding parallel dangerous frequency, the compensated impedance configuration is obtained.

6. The method according to claim 1, characterized in that, After obtaining the compensated impedance configuration, the method further includes: Using the compensated impedance configuration as the current configuration, the frequency sweep excitation signal is injected, and the compensated series branch phase margin spectrum and the compensated parallel branch phase margin spectrum are calculated. Verify that all phase margins in the compensated series branch phase margin spectrum and the compensated parallel branch phase margin spectrum are not lower than the preset phase margin safety threshold. If the verification fails, the impedance adjustment step size is reduced by a preset shrinkage ratio, and the steps of performing the corresponding impedance compensation strategy on the series branch energy storage unit and the parallel branch energy storage unit are returned based on the reduced impedance adjustment step size until the verification passes. The impedance configuration when the verification passes is then determined as the compensated impedance configuration.

7. The method according to claim 1, characterized in that, The generation of the hierarchical startup sequence based on the compensated impedance configuration includes: Based on the compensated impedance configuration, the maximum safe output boundary of each energy storage unit is calculated. Obtain the candidate set of energy storage units to be included in the startup sequence and the set of energy storage units already included in the startup sequence; For each candidate unit in the energy storage unit candidate set, calculate the combined impedance phase margin spectrum corresponding to its addition to the energy storage unit set, and extract the minimum phase margin in each combined impedance phase margin spectrum. The candidate unit corresponding to the maximum value in the minimum phase margin is determined as the startup unit of this stage, and the target value of the bus voltage after the startup of this stage is established is calculated based on the combined impedance configuration after the startup unit of this stage is added. The local start-up unit is added to the energy storage unit set. When the total capacity of the energy storage unit set is less than the preset target load capacity threshold, the local start-up unit is removed from the energy storage unit candidate set to update the energy storage unit candidate set. Then, the process returns to the step of calculating the combined impedance phase margin spectrum corresponding to each candidate unit in the energy storage unit candidate set after adding it to the energy storage unit set. When the total capacity of the energy storage unit set is not less than the target load capacity threshold, the recorded start-up units at each level and the corresponding bus voltage are combined according to the start-up order to generate the graded start-up sequence.

8. The method according to claim 1, characterized in that, The step of controlling the microgrid to complete a black start according to the hierarchical start sequence includes: The startup process is executed sequentially according to the hierarchical startup sequence, and the measured value of the bus voltage is collected after each startup is completed. Calculate the deviation amplitude between the measured value of the bus voltage and the target value of the corresponding bus voltage at this level; If the deviation amplitude exceeds the preset deviation range, the impedance configuration parameters of the next-level energy storage unit are corrected proportionally according to the deviation direction and magnitude of the deviation amplitude. Based on the corrected impedance configuration parameters, the system proceeds to the next stage of startup until the deviation between the measured value of the final bus voltage and the corresponding target value of the bus voltage does not exceed the preset deviation range, at which point the black start is confirmed to be complete.

9. A series-parallel grid-connected energy storage control system for improving black start of microgrids, characterized in that, The series-parallel grid-connected energy storage control system for improving microgrid black start includes: one or more processors and a memory; the memory is coupled to the one or more processors, the memory is used to store computer program code, the computer program code includes computer instructions, and the one or more processors call the computer instructions to cause the series-parallel grid-connected energy storage control system for improving microgrid black start to perform the method as described in any one of claims 1-8.

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