Energy storage type SOP black start method, system and device based on improved VSG networking control and medium

Abstract

The invention discloses an energy storage type SOP black-start method, system and device based on improved VSG network construction control and a medium, and relates to the field of power grid black-start, and the method comprises the steps: an energy storage type converter MMC carries out the active and reactive control based on an improved VSG network construction control strategy; a non-fault side MMC is controlled to firstly close an isolation circuit breaker and slowly charge a direct-current capacitor, and when the voltage reaches a set threshold value, a current-limiting resistor is quitted; the fault side MMC is started by the same step as the non-fault side MMC; after synchronization is completed, AC circuit breakers between the non-fault side MMC and the feeder load and between the fault side MMC and the feeder load are closed respectively; based on the collected power grid power data, MMC output parameters are adjusted to meet the power grid connection condition, the control mode is switched according to the grid connection state, and the black start process is ended. And by arranging the black start resistor for current-limiting charging and sub-module voltage balance control, the phenomena of overcurrent and voltage unbalance in the black start process are avoided.

Description

Technical Field

[0001] This invention relates to the field of black start in power grids, and in particular to a black start method, system, device and medium for energy storage-type SOP (Soft Open Point) based on improved VSG (Virtual Synchronous Generator) grid control. Background Technology

[0002] Intelligent soft switches, as a new type of power distribution network control device based on power electronics technology, are usually installed at the tie switches of the distribution network (such as between feeders or sectionalizing switch nodes). They realize AC-AC power conversion through topologies such as MMC (modular multilevel converter), which can flexibly adjust the active power distribution and reactive power compensation between different feeders, optimize network losses, smooth the fluctuation of new energy output, and quickly isolate fault areas and reconstruct the power supply network in the event of a fault, significantly improving the flexibility and reliability of the distribution network.

[0003] Black start is the process by which a power plant or power unit gradually establishes voltage and frequency using its own starting power source when the power system is completely de-energized and there is no external power supply. This allows it to gradually power other units and loads, ultimately restoring power. Currently, conventional black start methods for distribution networks have significant limitations: reliance on backfeeding from the upper-level grid is constrained by the grid's recovery progress and fails completely in scenarios of total grid outage; using diesel generators as black start power sources suffers from slow start-up, high pollution, and delayed output regulation, making it difficult to adapt to the dynamic power fluctuations of renewable energy distribution networks. In recent years, SOPs based on energy storage devices and converters have been increasingly applied to black start, but most existing methods employ grid-following control, relying on external power triggering and making it difficult to independently establish voltage and frequency. While traditional VSGs can simulate synchronous generator characteristics through droop control and achieve autonomous grid establishment, their droop coefficient and damping parameters are fixed, lacking adaptability to load disturbances and energy storage charge states, and are still prone to frequency and voltage fluctuations in scenarios with high renewable energy penetration.

[0004] Therefore, it is necessary to propose an energy storage-type SOP based on an improved VSG network control strategy. This SOP can establish stable voltage and frequency independently without relying on an external power grid, providing a reference power source for local areas of the distribution network and meeting the core requirement of "no external dependence" for black start. Relying on the topology characteristics of the SOP, the active / reactive power distribution between different feeders can be adjusted through VSG control, coordinating the power balance of multi-branch loads and distributed power sources during black start, avoiding single feeder overload, and solving the problem of poor compatibility of traditional black start with new energy sources. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention provides a black start method for energy storage-type SOP based on improved VSG network control.

[0006] Therefore, the problem to be solved by this invention is that although traditional VSG can simulate the characteristics of synchronous generators through droop control and achieve autonomous grid construction, its droop coefficient and damping parameters are fixed, and it lacks the ability to adapt to load disturbances and energy storage charge state. In scenarios with a high proportion of new energy penetration, it is still easy to cause frequency and voltage fluctuations.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a black start method for energy storage type SOP based on improved VSG network control, comprising: upon receiving a fault signal, disconnecting all circuit breakers to establish an initial safe state; starting the black start power supply, with the energy storage type converter MMC performing active and reactive power control based on the improved virtual synchronous generator VSG network control strategy; and starting the bidirectional DC-DC converter (Direct Current to Direct Current converter). The converter (DC-DC converter) controls the bidirectional flow of energy between the energy storage module and the capacitor; it gradually establishes the DC bus and AC output, controlling the non-faulty side MMC to first close the isolation circuit breaker and slowly charge the DC capacitor. When the voltage reaches the set threshold, the current-limiting resistor is removed, and the voltage of the upper and lower bridge arms is symmetrical through the capacitor voltage balancing algorithm; the faulty side MMC starts in the same steps as the non-faulty side MMC; the AC output voltage and frequency reference of the non-faulty side MMC are controlled by VSG to maintain them within the set error range, and the faulty side MMC starts with a delay and synchronizes the output parameters of the non-faulty side MMC; after synchronization, the AC circuit breakers between the non-faulty side MMC and the faulty side MMC and the feeder load are closed respectively, and the load is gradually increased from low load to rated capacity; based on the collected grid power data, the output parameters of all MMCs are adjusted to meet the grid connection conditions, and the control mode is switched according to the grid connection status, and finally the black start process ends.

[0008] As a preferred embodiment of the energy storage type SOP black start method based on improved VSG network control described in this invention, the step of disconnecting all circuit breakers includes disconnecting the interconnection circuit breakers between the power grids, disconnecting the connection circuit breakers between the feeder load and the power grid, and all connection circuit breakers between the energy storage type converter MMC and the external power grid, as well as the isolation circuit breaker between the MMC submodule and the DC bus, so that the intelligent soft switch SOP is in a physically isolated state, retaining only the electrical connection between the internal energy storage unit and the submodule.

[0009] As a preferred embodiment of the energy storage-based SOP black start method based on improved VSG network control described in this invention, the active and reactive power control includes active-frequency control and reactive-voltage control. The active-frequency control includes collecting frequency deviation, actual active power deviation, and energy storage state of charge, and determining the target value and allowable response range of frequency adjustment according to the current operating conditions and safety constraints, as input references for dynamic droop coefficient and equivalent inertia simulation. Based on the input references, an adaptive prediction method is used to generate dynamic droop coefficient and equivalent inertia value in real time, which are used to modify the droop and inertia parameters in the VSG model. After generating the dynamic adjustment amount, the adjustment command is constrained and allocated according to a preset safety and coordination strategy.

[0010] As a preferred embodiment of the energy storage-type SOP black start method based on improved VSG network control described in this invention, the reactive power-voltage control includes: collecting the output voltage amplitude, reactive power deviation, and energy storage state of charge of the energy storage converter as input variables to construct dynamic voltage regulation control requirements, and determining the target voltage range and allowable deviation interval; generating a reactive power-voltage droop coefficient based on the input variables using a dynamic adaptive control strategy; and correcting and compensating for the steady-state deviation using a steady-state error correction mechanism with adaptive adjustment capabilities based on the dynamic droop control.

[0011] The beneficial effects of this preferred technical solution are as follows: Based on conventional reactive power-voltage control, a dynamic droop and steady-state error correction mechanism is introduced to effectively suppress voltage fluctuations, quickly establish and maintain the grid voltage, and facilitate the rapid and shock-free connection of subsequent grid-connected equipment such as photovoltaic inverters.

[0012] As a preferred embodiment of the energy storage-type SOP black-start method based on improved VSG network control described in this invention, wherein: controlling the bidirectional energy flow between the energy storage module and the capacitor includes, The bidirectional DC-DC converter is configured to be compatible with both boost and buck duplex modes. It operates in boost mode when the energy storage module charges the DC capacitor, and in buck mode when the capacitor feeds back energy to the energy storage module. Based on the operating parameters of the MMC DC bus, the current load demand and energy storage status are determined in real time, and the corresponding energy flow direction and DC-DC operating mode are selected. The energy transmission rate is controlled by a current control strategy. A state-of-charge (SOC) equalization control is introduced to dynamically allocate power transmission commands according to the SOC of each energy storage unit.

[0013] As a preferred embodiment of the energy storage-type SOP black-start method based on improved VSG network control described in this invention, the step of achieving symmetrical voltage between the upper and lower bridge arms through a capacitor voltage balancing algorithm includes: Based on the capacitor voltage equalization control method, the switching status of each sub-module of the upper and lower bridge arms is adjusted to suppress the operation fluctuation of each sub-module in the bridge arm; during operation, the symmetry of the bridge arm voltage is continuously detected, and when the voltage deviation between the upper and lower bridge arms exceeds the set threshold, a fast adjustment strategy is triggered to reduce the deviation.

[0014] The beneficial effects of this preferred technical solution are: enhanced bridge arm symmetry can significantly reduce the harmonic content of MMC output, improve the sinusoidal nature and stability of output voltage during grid construction, and facilitate the normal connection of back-end equipment such as new energy inverters.

[0015] As a preferred embodiment of the energy storage-type SOP black start method based on improved VSG grid control described in this invention, the step of switching the control mode according to the grid connection status includes first connecting to the non-faulty side and switching the control mode to constant DC voltage control, and then connecting to the faulty side and switching to constant power control; the conditions for the black start process to end include when the AC side voltage fluctuation is less than or equal to 1%, the frequency fluctuation is ±0.1Hz, and the AC grid load recovers to 80% or more of the rated capacity, the black start process is determined to be completed.

[0016] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a system for a black start method of energy storage type SOP based on improved VSG network control, comprising: a circuit breaker module, a pre-start module, a start module, and a grid connection module; the circuit breaker module disconnects all circuit breakers after receiving a fault signal to establish an initial safe state; the pre-start module starts the black start power supply, and the energy storage converter MMC performs active and reactive power control based on the improved virtual synchronous generator VSG network control strategy, and starts the bidirectional DC-DC converter to control the bidirectional energy flow between the energy storage module and the capacitor; the start module gradually establishes the DC bus and AC output, and controls the non-faulty side MMC to first close the isolation circuit breaker and slowly connect the DC capacitor. During charging, once the voltage reaches a set threshold, the current-limiting resistor is removed, and the voltage of the upper and lower bridge arms is made symmetrical through a capacitor voltage balancing algorithm. The fault-side MMC starts up in the same steps as the non-fault-side MMC. The AC output voltage and frequency reference of the non-fault-side MMC are controlled by VSG to maintain them within the set error range. The fault-side MMC starts up with a delay and synchronizes the output parameters of the non-fault-side MMC. After synchronization, the AC circuit breakers between the non-fault-side MMC and the fault-side MMC and the feeder load are closed respectively, and the load is gradually increased from low load to rated capacity. The grid connection module adjusts the output parameters of all MMCs to meet the grid connection conditions based on the collected grid power data, and switches the control mode according to the grid connection status. Finally, the black start process ends.

[0017] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the energy storage type SOP black start method based on improved VSG network control as described above.

[0018] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of an energy storage-type SOP black-start method based on improved VSG network control as described above.

[0019] The beneficial effects of this invention are as follows: The energy storage-type MMC can simulate the inertia and droop characteristics of a synchronous generator, and adaptively adjust control parameters according to power deviation, voltage deviation, and energy storage state of charge. This allows it to autonomously establish stable AC voltage and frequency even in a grid-wide power outage scenario, without relying on an external power source reference, thus solving the problem of external calibration required by traditional methods. By setting a black-start resistor for current-limited charging and submodule voltage balancing control, overcurrent and voltage imbalance during black-start are avoided, ensuring the safety of the converter and energy storage device.

[0020] This invention, through steps such as phased load-bearing and pre-synchronous grid connection, is easy to implement in engineering, can effectively shorten black start time, and provide a guarantee for the rapid restoration of power supply to the power grid. Attached Figure Description

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

[0022] Figure 1 This is a flowchart of an energy storage-type SOP black start method based on improved VSG network control in Example 1.

[0023] Figure 2 This is a structural diagram of an energy storage-type SOP black start method based on improved VSG network control in Example 2. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0026] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides a black start method for energy storage-type SOP based on improved VSG network control, including: S1: Upon receiving a fault signal, disconnect all circuit breakers to establish an initial safe state.

[0027] S2: After starting the black start power supply, the energy storage converter MMC performs active and reactive power control based on the improved virtual synchronous generator VSG network control strategy.

[0028] S3: Start the bidirectional DC-DC converter to control the bidirectional flow of energy between the energy storage module and the capacitor.

[0029] S4: Gradually establish the DC bus and AC output, control the non-faulty side MMC to first close the isolation circuit breaker and slowly charge the DC capacitor. When the voltage reaches the set threshold, the current limiting resistor is removed, and the voltage of the upper and lower bridge arms is made symmetrical through the capacitor voltage balancing algorithm.

[0030] S5: The faulty-side MMC starts up using the same steps as the non-faulty-side MMC.

[0031] S6: Controls the AC output voltage and frequency reference of the non-faulty side MMC through VSG, keeping them within the set error range, delaying the start-up of the faulty side MMC and synchronizing the output parameters of the non-faulty side MMC.

[0032] S7: After synchronization is completed, close the AC circuit breakers between the non-faulty MMC and the faulty MMC and the feeder load respectively, and gradually increase the load from low load to rated capacity.

[0033] S8: Based on the collected power grid data, adjust all MMC output parameters to meet the grid connection conditions, and switch the control mode according to the grid connection status, and finally the black start process ends.

[0034] It should be noted that traditional black start methods for distribution networks generally rely on backfeed power from the upstream grid or diesel generators as starting power sources. Once the entire grid is out of power or in an islanded state, voltage and frequency references cannot be provided, and the starting capability is completely lost. Existing SOP devices or energy storage-type MMCs mostly adopt current source or phase-locked loop control methods, which can only operate under the existing grid reference. This is a "follower" operation mode, which cannot independently construct voltage and frequency references under the condition of no grid reference, and does not have the autonomous grid construction capability required in the initial stage of black start.

[0035] Therefore, in response to the above problems, such as Figure 1As shown, this invention, through steps S1-S8, firstly, upon receiving a fault signal, fully isolates the converter system, establishing an initial safe state of physical disconnection. Then, it starts the non-faulty side energy storage converter with grid connection capability, achieving dynamic adjustment of active and reactive power based on an improved VSG control strategy, and completing energy interaction between the energy storage module and the DC capacitor through a bidirectional DC-DC converter. Based on completing DC bus charging and sub-module voltage balancing, a stable AC output reference is established, and the faulty side converter is driven to achieve consistent multi-machine operation through master-slave synchronization. Subsequently, the system gradually loads to the target load level, and after completing frequency, voltage, and phase matching, it successfully connects to the external grid. Simultaneously, it automatically switches control modes according to the grid connection status, ensuring a smooth transition during black start and continuous power restoration.

[0036] Example 2, refer to Figure 2 This is the second embodiment of the present invention, which differs from the first embodiment in that: a black start method for energy storage-type SOP based on improved VSG network control further includes, as... Figure 2 As shown, the VSG-based grid-controlled energy storage SOP of the present invention includes a first AC circuit breaker QF1, a second AC circuit breaker QF2, a third AC circuit breaker QF3, a fourth AC circuit breaker QF4; a first transformer T1, a second transformer T2; a first feeder load Pload1, a second feeder load Pload2; a first DC circuit breaker DCCB1, a second DC circuit breaker DCCB2, a third DC circuit breaker DCCB3, a fourth DC circuit breaker DCCB4, a fifth DC circuit breaker DCCB5, a sixth DC circuit breaker DCCB6, a seventh DC circuit breaker DCCB7, an eighth DC circuit breaker DCCB8; a first energy storage modular multilevel voltage source converter MMC1, a second energy storage modular multilevel voltage source converter MMC2; a DC capacitor Cdc; and a black starting resistor Rx.

[0037] Furthermore, in this embodiment, if the first feeder load fails, then MMC1 is the fault-detecting MMC and MMC2 is the non-fault-detecting MMC. In step S1, disconnecting all circuit breakers includes disconnecting the interconnection circuit breaker between the power grid, disconnecting the connection circuit breaker between the feeder load and the power grid, disconnecting all connection circuit breakers between the energy storage converter MMC and the external power grid, and disconnecting the isolation circuit breaker between the MMC submodule and the DC bus, so that the smart soft switch SOP is in a physically isolated state, retaining only the electrical connection between the internal energy storage unit and the submodule.

[0038] Specifically, disconnect the interconnecting circuit breaker between the two AC power grids, disconnect the AC circuit breaker QF1 connecting feeder load 1 (Pload1) to AC power grid 1, the connecting circuit breaker QF3 connecting feeder load 2 (Pload2) to AC power grid 2, and all connecting circuit breakers QF2 and QF4 connecting the two energy storage MMCs (MMC1, MMC2) to the external power grid, as well as the DC circuit breakers DCCB1, DCCB3, DCCB5, and DCCB7 between the MMC submodules and the DC bus, ensuring that the SOP is in a physically isolated state, retaining only the electrical connection between the internal energy storage unit and the submodule. At this time, the black-start power supply can be selected for no-load start-up, or start-up load with 5% of the rated capacity (such as the core control circuit power supply), avoiding voltage fluctuations caused by complete no-load.

[0039] Confirm that all submodules (IGBTs, diodes, capacitors, and embedded energy storage) are fault-free, the bridge arm reactor parameters are normal, and the DC line isolating switches DCCB2, DCCB4, DCCB6, and DCCB8 are initially in the open state. The black start resistor (R) is functioning correctly. x Connected in series to the positive and negative circuits on the DC side.

[0040] Furthermore, in step S2, active and reactive power control includes active-frequency control and reactive-voltage control. Active-frequency control includes the following steps B1-B3: B1: Collect frequency deviation, actual active power deviation and energy storage state of charge, and determine the target value and allowable response range of frequency adjustment based on the current operating conditions and safety constraints, as input references for dynamic droop coefficient and equivalent inertia simulation.

[0041] B2: Based on the input reference, an adaptive prediction method is used to generate dynamic droop coefficients and equivalent inertia values ​​in real time, which are used to modify the droop and inertia parameters in the VSG model.

[0042] B3: After generating the dynamic adjustment amount, the adjustment command is constrained and allocated according to the preset safety and coordination strategy.

[0043] Specifically, the external characteristics of a synchronous generator are modeled using the rotor motion equations of the synchronous generator, as expressed by the formula: in, , These are the actual angular velocity and the rated angular velocity, respectively. For time, This represents the rate of change of the actual angular velocity over time. , These are mechanical torque and electromagnetic torque, respectively. The damping coefficient is... Let be the moment of inertia.

[0044] To achieve adaptive frequency modulation, this invention introduces an adaptive prediction method. In the embodiments of this application, step B2 employs dynamic frequency control based on a fuzzy predictor, including the following steps B211-B213: B211: Obtain system frequency deviation, active power deviation, and energy storage state of charge (SOC), and set the target frequency adjustment range.

[0045] B212: Input the above three input quantities into the fuzzy predictor, perform fuzzification processing on the control variables based on the fuzzy rule base and membership function, calculate the dynamic frequency droop coefficient, and realize the adaptive adjustment of the droop coefficient.

[0046] B213: The predicted droop coefficient is fed back to the VSG control loop to dynamically adjust the VSG output frequency, thereby achieving a rapid response to load disturbances and changes in energy storage status.

[0047] Specifically, based on power deviation , Reference power, frequency deviation And the State of Charge (SOC) of energy storage is used to predict the dynamic droop factor. The control relationship is expressed as: The improved rotor motion equation of the synchronous generator is expressed as: In an optional implementation, the adaptive prediction method may also employ dynamic frequency control based on model predictive control, including the following steps B221-B223: B221: Establish a simplified discrete state-space model of the energy storage MMC system and acquire state variables such as system frequency deviation, active power deviation and SOC in real time.

[0048] B222: With the goal of minimizing frequency error and power deviation over a future period, a predictive control optimization problem is constructed, and constraints such as SOC, current, and voltage are applied. The optimal control input—the dynamic droop coefficient—is obtained by solving the problem in the rolling time domain.

[0049] B223: Apply the dynamic droop coefficient to the VSG control framework to adjust the frequency response characteristics and achieve feedforward prediction and constraint optimization control of power disturbances.

[0050] In another alternative implementation, the adaptive prediction method may also employ dynamic frequency regulation based on gain-scheduled PID (Proportional-Integral-Derivative) control, including the following steps B231-B233: B233: Set the set of control gains corresponding to different operating conditions (such as high / low SOC, large / small frequency deviation), and monitor the system operating status (frequency error, active power fluctuation, SOC, etc.) in real time.

[0051] B233: Based on the current operating conditions, the corresponding PID controller gain coefficient is obtained through matching or interpolation. The current frequency control quantity is calculated through proportional, integral, and derivative three-loop regulation, which is used to construct the dynamic frequency droop curve.

[0052] B233: The output frequency adjustment is applied to the VSG model to dynamically update its output frequency, thereby improving frequency stability and adjustment sensitivity, and adapting to different states of charge and load fluctuation conditions.

[0053] It should be noted that by introducing multiple prediction or regulation mechanisms such as fuzzy prediction, MPC, and adaptive PID, the frequency response parameters can be dynamically adjusted based on frequency deviation, active power fluctuations, and the state of charge (SOC) of the energy storage system. This enhances the system's ability to track frequency disturbances. Compared to the traditional VSG control method with fixed droop parameters, the scheme of dynamically adjusting the droop coefficient improves system stability and robustness, making it particularly suitable for complex operating conditions such as high-proportion renewable energy integration and reduced grid inertia. The regulation process considers the SOC state, preventing over-discharge or impact operation of the energy storage system during frequency support, thus improving the system's lifespan and energy efficiency ratio.

[0054] Furthermore, reactive power-voltage control includes the following steps B4-B6: B4: Collect the output voltage amplitude, reactive power deviation, and energy storage state of charge of the energy storage converter as input variables to construct dynamic voltage regulation control requirements, and determine the target voltage range and allowable deviation interval.

[0055] B5: Based on the input variables, a dynamic adaptive control strategy is used to generate the reactive power-voltage droop coefficient.

[0056] B6: Based on dynamic droop control, a steady-state error correction mechanism with adaptive adjustment capability is adopted to correct and compensate for steady-state deviation.

[0057] Specifically, reactive power-voltage control is expressed using the droop control formula as follows: in, For reference reactive power, This refers to the actual output reactive power. The output voltage amplitude, This is the rated voltage amplitude. This is the reactive power droop coefficient.

[0058] In this embodiment of the application, in step B6, the steady-state error correction mechanism adopts an error correction mechanism based on fuzzy prediction and integral compensation, including the following steps B611-B613: B611: Based on voltage deviation reactive power deviation And SOC, generating reactive power-voltage droop coefficient The formula is expressed as: B612: The improved frequency adjustment relationship is expressed as follows: in, This is the dynamic reactive power droop coefficient output by fuzzy prediction.

[0059] B613: Meanwhile, to further enhance the steady-state performance of the voltage, an integral term is added to the reactive power control, resulting in the optimized formula: in, This is the reactive integral gain.

[0060] In an optional implementation, the steady-state error correction mechanism can also employ an error correction mechanism based on a dual-loop control structure, including the following steps B621-B623: B621: Construct an outer-loop voltage regulation channel with voltage deviation as input, set a voltage control target, and sample the deviation between the output voltage value and the target value in real time.

[0061] B622: Converts voltage error into target reactive current command via a proportional-integral controller (or other regulator) and transmits it to the inner loop.

[0062] B623: The internal loop current controller adjusts the actual reactive current output at high speed to ensure that the reactive current tracks the target value, thereby achieving stable regulation and error correction of the system voltage, especially with good error suppression capability under steady-state operation.

[0063] In another alternative implementation, the steady-state error correction mechanism may also employ an error correction mechanism based on feedforward-feedback composite control, including the following steps B631-B633: B631: Establish a feedforward mapping model between voltage disturbance and load change, predict future voltage fluctuations by detecting load change trends, and calculate the feedforward compensation amount.

[0064] B632: Real-time monitoring of the error between the output voltage and the target value, constructing a feedback control channel, and calculating the feedback correction amount through means such as PI regulator.

[0065] B633: It integrates and superimposes the feedforward compensation and feedback correction to form a composite regulation command that acts on the reactive power output port of the converter, thereby achieving rapid compensation and dynamic suppression of voltage error under steady state and improving system responsiveness and voltage stability.

[0066] It should be noted that by introducing dynamic droop and steady-state error correction mechanisms (such as integral compensation and dual-loop control) on the basis of conventional reactive power-voltage control, voltage fluctuations can be effectively suppressed, and grid voltage can be quickly established and maintained stably. Multiple control strategies (such as fuzzy control and feedforward-feedback composite control) are supported, allowing for flexible selection of adjustment methods based on operating conditions, thus improving the universality and engineering deployment flexibility of the control system. The steady-state error correction mechanism ensures that system voltage deviation is controllable during long-term operation, facilitating rapid and shock-free grid connection of subsequent grid-connected equipment such as photovoltaic inverters.

[0067] Furthermore, in step S3, controlling the bidirectional flow of energy between the energy storage module and the capacitor includes the following steps C1-C3: C1: Configure the bidirectional DC-DC converter to be compatible with both boost and buck duplex modes. It operates in boost mode when the energy storage module charges the DC capacitor, and in buck mode when the capacitor feeds energy back to the energy storage module.

[0068] C2: Based on the operating parameters of the MMC DC bus, determine the current load demand and energy storage status in real time, select the corresponding energy flow direction and DC-DC working mode, and control the energy transmission rate through current control strategy.

[0069] C3: Introducing state-of-charge (SOC) equalization control, which dynamically allocates power transmission commands based on the SOC of each energy storage unit.

[0070] In this embodiment of the application, in step C2, the current control strategy adopts a current-limiting current control strategy based on dual closed-loop control, including the following steps C211-C213: C213: Construct a dual closed-loop control structure with inductor current as the inner loop and capacitor voltage as the outer loop. The inner loop uses a fast PI controller to adjust the duty cycle and control the actual current to quickly track the command value. The outer loop aims to maintain the DC bus voltage stability.

[0071] C213: Calculate the desired current command based on the voltage difference between the energy storage module voltage and the bus voltage, and limit it according to the maximum charge and discharge current limit to prevent current overshoot.

[0072] C213: Inputs current command to the inner loop for closed-loop regulation to achieve a smooth charging / discharging process, ensures that the rate of current change is controlled, thereby controlling the energy transfer rate and ensuring system safety.

[0073] In an optional implementation, the current control strategy may also employ a dynamic current limiting strategy based on hysteresis control, including the following steps C221-C223: C223: Set the upper and lower limits of the target current to form a hysteresis interval, sample the inductor current and compare it with the reference upper and lower limits in real time.

[0074] C223: When the current reaches the upper limit, the duty cycle is immediately reduced to decrease the current; when the current drops to the lower limit, the duty cycle is increased to increase the current, thus achieving dynamic switching regulation.

[0075] C223: By adjusting the hysteresis bandwidth and current setting range, the switching frequency and average current are controlled, thereby indirectly controlling the energy transfer rate and adapting to dynamic fluctuations in the energy storage SOC or bus voltage.

[0076] In another alternative implementation, the current control strategy may also employ a fast current regulation strategy based on feedforward + feedback composite control, including the following steps C231-C233: C231: Based on the expected rate of change of bus voltage and the current load power demand, calculate the target current feedforward value and estimate the required charging / discharging current in advance.

[0077] C232: By combining real-time acquired current and voltage errors, a feedback controller is designed to adjust the current command and correct the prediction error.

[0078] C233: The feedforward compensation and feedback correction are superimposed to form the final current control target, which controls the duty cycle of the DC-DC converter to achieve fast and stable current regulation, thereby achieving fine energy transfer rate control.

[0079] It should be noted that by switching between boost / buck modes and using SOC sensing, bidirectional energy flow regulation from energy storage to capacitors or from capacitors to energy storage is achieved, effectively supporting load fluctuations and DC bus voltage control requirements. Combined with current limiting control, duty cycle regulation, and current feedback mechanisms, problems such as capacitor overvoltage and current surges caused by sudden power changes are prevented, ensuring the safe operation of the energy storage device and the converter. Combined with SOC balancing strategies, complementary power supply based on the DC bus can be achieved between different MMCs, improving flexibility and system redundancy during black start-up.

[0080] Furthermore, in step S4, the voltage symmetry of the upper and lower bridge arms is achieved through a capacitor voltage balancing algorithm, including the following steps D1-D2: D1: Based on the capacitor voltage equalization control method, the switching status of each sub-module in the upper and lower bridge arms is adjusted to suppress the operation fluctuation of each sub-module in the bridge arm.

[0081] D2: During operation, the symmetry of the bridge arm voltage is continuously detected. When the voltage deviation between the upper and lower bridge arms exceeds the set threshold, a fast adjustment strategy is triggered to reduce the deviation.

[0082] In this embodiment of the application, in step D1, the capacitor voltage equalization control method adopts equalization control based on periodic sampling and submodule rotation, including the following steps D111-D113: D111: Collect the capacitor voltage values ​​of all sub-modules in the upper and lower bridge arms at fixed intervals (e.g., every 5ms), and calculate the total voltage difference between the upper and lower bridge arms and the voltage distribution status between each sub-module.

[0083] D112: Based on the voltage sorting results, submodules with higher voltages are prioritized to exit operation, while submodules with lower voltages are prioritized to start operation. They are replaced sequentially according to a preset rotation order to achieve dynamic voltage balance among modules.

[0084] D113: Continuously performs sampling and rotation adjustment to ensure that the bridge arm voltage deviation is maintained within the set tolerance range (e.g., ≤50V) during dynamic operation, thereby achieving stable bridge arm symmetry.

[0085] In an optional implementation, the capacitor voltage equalization control method may also employ adaptive submodule regulation based on a minimum deviation optimization strategy, including the following steps D121-D123: D123: Real-time acquisition of capacitor voltages in each submodule and calculation of total voltage deviation between upper and lower bridge arms to construct the voltage balancing objective function of the current system.

[0086] D123: From the sub-modules to be added, prioritize the module with the voltage closest to the target average voltage to add to the bridge arm operation; from the modules to be removed, prioritize the module with the largest deviation from the target voltage to disconnect, so that each switching operation is optimized in the direction of balance.

[0087] D123: This optimal matching strategy minimizes voltage imbalance in each round of control action, thereby improving voltage balancing response efficiency and bridge arm symmetry stability.

[0088] In another alternative implementation, the capacitor voltage equalization control method may also employ adaptive submodule regulation based on a minimum deviation optimization strategy, including the following steps D131-D133: D131: Continuously monitor the deviation between the capacitor voltage of each submodule in the upper and lower bridge arms and the target voltage of the bus, and establish a voltage difference mapping relationship between modules.

[0089] D132: Without changing the number of submodules switched on or off, the PWM duty cycle of individual submodules is adjusted to make fine adjustments by changing the proportion of their output voltage, thus forming a "fine-grained" voltage correction method.

[0090] D133: Eliminates minor voltage imbalances through an adaptive duty cycle adjustment mechanism, making it particularly suitable for symmetrical and precise voltage control scenarios with small load changes or small voltage differences between sub-modules.

[0091] It should be noted that by employing real-time balancing control strategies (such as rotation, minimum deviation optimization, and duty cycle fine-tuning), the output voltage of the upper and lower bridge arms is ensured to be symmetrical. This effectively prevents asymmetrical waveforms or internal circulating currents caused by bridge arm skew. Enhanced bridge arm symmetry significantly reduces the harmonic content of the MMC output, improves the sinusoidal nature and stability of the output voltage during grid construction, and facilitates the normal connection of back-end equipment such as new energy inverters. Dynamically controlling the engagement / disengagement status of submodules can suppress the long-term high-load operation of some submodules, improving the overall module lifespan and system operational balance.

[0092] Furthermore, in step B6, after the DC bus voltage stabilizes, the energy storage type MMC2 establishes the AC distribution network reference voltage V on both sides within 100ms through VSG control. acref With ±2% voltage and 50Hz±0.1Hz frequency, the initial SOC of the embedded energy storage submodule is maintained at 40%-70%; the energy storage type MMC1 starts up with a 50ms delay, synchronizes the parameters of the energy storage type MMC2 and fine-tunes the phase (phase difference ≤1°), and achieves dual-machine synchronization.

[0093] Furthermore, in step B7, after synchronization, energy storage type MMC1 and energy storage type MMC2 close the AC circuit breakers QF2 and QF4 connected to Pload1 and Pload2 respectively, gradually increasing the rated load from 30% to 100%, and the DC side responds to the power demand in real time: when the AC side load suddenly increases, the energy storage discharges to the DC bus through the bidirectional DC-DC converter (response ≤50ms) to maintain the DC voltage stability; if the energy storage SOC of energy storage type MMC2 drops to 30%, energy storage type MMC1 transmits power to it through the DC tie line (DC side voltage fluctuation ≤±50V), and at the same time, the SOC equalization control ensures that the SOC of both machines is ≥30%.

[0094] Furthermore, in step S8, pre-synchronization detection is first performed. Energy storage type MMC1 and energy storage type MMC2 respectively collect the voltage, frequency and phase of the corresponding AC grid. The AC side parameters are finely adjusted to within the deviation threshold (voltage difference ≤ 500V, frequency difference ≤ 0.1Hz, phase difference ≤ 3°) through VSG. At the same time, the DC bus voltage is adjusted to match the grid-side converter station (deviation ≤ 200V).

[0095] After the grid connection conditions are met, the control mode is switched according to the grid connection status, including first connecting to the non-faulty side and switching the control mode to constant DC voltage control, and then connecting to the faulty side and switching to constant power control.

[0096] Specifically, first close the AC interconnection circuit breaker QF3 between the energy storage MMC2 and AC grid 2. Simultaneously, the control mode of the energy storage MMC2 changes from grid-connected control to the traditional constant DC voltage control mode. At this time, the energy storage MMC is only used to smooth grid surges. After a 1-second delay, the energy storage MMC1 is connected to AC grid 1, and the control mode switches to constant power control mode.

[0097] The conditions for the black start process to end include: when the AC side voltage fluctuation is less than or equal to 1%, the frequency fluctuation is ±0.1Hz, and the AC grid load recovers to 80% or more of the rated capacity, the black start process is considered complete.

[0098] Example 3, the third embodiment of the present invention, differs from the previous two embodiments in that it is an energy storage-type SOP black start system based on improved VSG network control, including a circuit breaker module, a pre-start module, a start module, and a grid connection module. Upon receiving a fault signal, the circuit breaker module disconnects all circuit breakers to establish an initial safe state. The pre-start module starts the black start power supply, and the energy storage converter MMC performs active and reactive power control based on the improved virtual synchronous generator VSG network control strategy, starting the bidirectional DC-DC converter to control bidirectional energy flow between the energy storage module and the capacitor. The start module gradually establishes the DC bus and AC output, controlling the non-faulty side MMC to first close the isolation circuit breaker and slowly connect the DC capacitor. During charging, once the voltage reaches the set threshold, the current-limiting resistor is removed, and the voltage of the upper and lower bridge arms is made symmetrical through a capacitor voltage balancing algorithm. The fault-side MMC starts up in the same steps as the non-fault-side MMC. The AC output voltage and frequency reference of the non-fault-side MMC are controlled by VSG to keep them within the set error range. The fault-side MMC starts up with a delay and synchronizes the output parameters of the non-fault-side MMC. After synchronization, the AC circuit breakers between the non-fault-side MMC and the fault-side MMC and the feeder load are closed respectively, and the load is gradually increased from low load to rated capacity. The grid connection module adjusts the output parameters of all MMCs to meet the grid connection conditions based on the collected grid power data, and switches the control mode according to the grid connection status. Finally, the black start process ends.

[0099] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0100] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0101] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0102] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented in combination with any of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0103] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A black start method for energy storage-type SOP based on improved VSG network control, characterized in that: include, Upon receiving a fault signal, disconnect all circuit breakers to establish an initial safe state; After the black-start power supply is started, the energy storage converter MMC performs active and reactive power control based on the improved virtual synchronous generator VSG network control strategy. The bidirectional DC-DC converter is activated to control the bidirectional flow of energy between the energy storage module and the capacitor. Gradually establish the DC bus and AC output, control the non-faulty side MMC to first close the isolation circuit breaker and slowly charge the DC capacitor, and when the voltage reaches the set threshold, exit the current limiting resistor, and make the voltage of the upper and lower bridge arms symmetrical through the capacitor voltage balancing algorithm. The faulty-side MMC is started using the same procedures as the non-faulty-side MMC. The AC output voltage and frequency reference of the non-faulty side MMC are controlled by VSG to maintain them within the set error range, and the faulty side MMC starts up with a delay and synchronizes the output parameters of the non-faulty side MMC. After synchronization is completed, close the AC circuit breakers between the non-faulty MMC and the faulty MMC and the feeder load respectively, and gradually increase the load from low load to rated capacity. Based on the collected power grid data, all MMC output parameters are adjusted to meet the grid connection conditions, and the control mode is switched according to the grid connection status, and finally the black start process ends.

2. The energy storage-type SOP black start method based on improved VSG network control as described in claim 1, characterized in that: Disconnecting all circuit breakers includes disconnecting the interconnection circuit breakers between the power grids, disconnecting the connection circuit breakers between the feeder load and the power grid, and disconnecting all connection circuit breakers between the energy storage converter MMC and the external power grid, as well as the isolation circuit breaker between the MMC submodule and the DC bus, so that the smart soft switch SOP is in a physically isolated state, retaining only the electrical connection between the internal energy storage unit and the submodule.

3. The energy storage-type SOP black start method based on improved VSG network control as described in claim 2, characterized in that: The active and reactive power control includes active power-frequency control and reactive power-voltage control, wherein the active power-frequency control includes, Collect frequency deviation, actual active power deviation and energy storage state of charge, and determine the target value and allowable response range of frequency regulation based on the current operating conditions and safety constraints, as input references for dynamic droop coefficient and equivalent inertia simulation; Based on the input reference, an adaptive prediction method is used to generate dynamic droop coefficients and equivalent inertia values ​​in real time, which are then used to modify the droop and inertia parameters in the VSG model. After generating the dynamic adjustment amount, the adjustment command is constrained and allocated according to the preset safety and coordination strategy.

4. The energy storage-type SOP black start method based on improved VSG network control as described in claim 3, characterized in that: The reactive power-voltage control includes, The output voltage amplitude, reactive power deviation, and energy storage state of charge of the energy storage converter are collected as input variables to construct the dynamic voltage regulation control requirements and determine the target voltage range and allowable deviation range. Based on the input variables, a dynamic adaptive control strategy is used to generate the reactive power-voltage droop coefficient. Based on dynamic droop control, a steady-state error correction mechanism with adaptive adjustment capability is adopted to correct and compensate for steady-state deviation.

5. The energy storage-type SOP black start method based on improved VSG network control as described in claim 4, characterized in that: The control of bidirectional energy flow between the energy storage module and the capacitor includes... The bidirectional DC-DC converter is configured to be compatible with both boost and buck duplex modes. It operates in boost mode when the energy storage module charges the DC capacitor, and in buck mode when the capacitor feeds energy back to the energy storage module. Based on the operating parameters of the MMC DC bus, the current load demand and energy storage status are determined in real time, and the corresponding energy flow direction and DC-DC working mode are selected. The energy transmission rate is controlled through the current control strategy. A state-of-charge (SOC) equalization control is introduced to dynamically allocate power transmission commands based on the SOC of each energy storage unit.

6. The energy storage-type SOP black start method based on improved VSG network control as described in claim 5, characterized in that: The method of achieving voltage symmetry between the upper and lower bridge arms through a capacitor voltage equalization algorithm includes... Based on the capacitor voltage equalization control method, the switching status of each sub-module in the upper and lower bridge arms is adjusted to suppress the operation fluctuations of each sub-module in the bridge arm. During operation, the symmetry of the bridge arm voltage is continuously detected. When the voltage deviation between the upper and lower bridge arms exceeds the set threshold, a fast adjustment strategy is triggered to reduce the deviation.

7. The energy storage-type SOP black start method based on improved VSG network control as described in claim 6, characterized in that: The control mode switching according to grid connection status includes first connecting to the non-faulty side and switching the control mode to constant DC voltage control, and then connecting to the faulty side and switching to constant power control. The conditions for the black start process to end include: when the AC side voltage fluctuation is less than or equal to 1%, the frequency fluctuation is ±0.1Hz, and the AC grid load recovers to 80% or more of the rated capacity, the black start process is determined to be complete.

8. A black-start energy storage system based on improved VSG network control, employing the black-start energy storage system based on improved VSG network control as described in any one of claims 1 to 7, characterized in that: It includes a circuit breaker module, a pre-start module, a start module, and a grid connection module; After receiving a fault signal, the circuit breaker module disconnects all circuit breakers and establishes an initial safe state. The pre-start module starts the black start power supply, and the energy storage converter MMC performs active and reactive power control based on the improved virtual synchronous generator VSG network control strategy. It also starts the bidirectional DC-DC converter to control the bidirectional flow of energy between the energy storage module and the capacitor. The startup module gradually establishes the DC bus and AC output, controls the non-faulty MMC to first close the isolation circuit breaker and slowly charge the DC capacitor. When the voltage reaches the set threshold, the current limiting resistor is removed, and the voltage of the upper and lower bridge arms is made symmetrical through the capacitor voltage balancing algorithm. The faulty MMC starts in the same steps as the non-faulty MMC. The AC output voltage and frequency reference of the non-faulty MMC are controlled by VSG to keep them within the set error range. The faulty MMC starts with a delay and synchronizes the output parameters of the non-faulty MMC. After synchronization, the AC circuit breakers between the non-faulty MMC and the faulty MMC and the feeder load are closed respectively, and the load is gradually increased from low load to rated capacity. The grid connection module adjusts all MMC output parameters to meet the grid connection conditions based on the collected grid power data, and switches the control mode according to the grid connection status, and finally the black start process ends.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the energy storage-type SOP black start method based on improved VSG network control as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the energy storage-type SOP black start method based on improved VSG network control as described in any one of claims 1 to 7.

Images