Parallel and off-grid switching control method in terminal string parallel type source network load storage network energy storage

Abstract

This invention relates to the field of grid energy storage control technology, aiming to provide a grid-connected / off-grid switching control method for end-point series-parallel source-grid-load-storage grid-connected energy storage systems. The method includes: when switching from off-grid to grid-connected operation, first determining whether the voltage amplitude difference and phase difference between the inverter and the public grid simultaneously meet preset grid-connection conditions; if so, closing the grid-connection switch to connect the AC bus to the public grid; if not, adjusting the voltage amplitude or phase output of the inverter until the grid-connection conditions are met; when switching from grid-connected to off-grid operation, disconnecting the grid-connection switch and simultaneously adjusting the reference active power to 0, thus achieving the state switch from grid-connected to off-grid. This invention enables the end-point energy storage system to have good dynamic and steady-state performance under both grid-connected and off-grid switching conditions, meeting the requirements of both operating modes; ensuring a smooth mode switching process, and improving the flexibility and stability of grid-connected / off-grid switching.

Description

Technical Field

[0001] This invention relates to the field of power grid energy storage control technology, specifically to a control method for grid-to-off-grid switching in a grid-to-grid energy storage system with end-point series-parallel source-grid-load-storage configuration. Background Technology

[0002] In recent years, with the increasing penetration rate of new energy sources such as wind power and photovoltaics, the highly electronic nature of power grids has become increasingly prominent, posing significant technical challenges to their safe and stable operation. Off-grid and grid-connected modes of energy storage systems offer substantial advantages in improving power supply reliability and promoting the efficient absorption of new energy sources.

[0003] Off-grid operation of energy storage systems requires a voltage source to provide system voltage amplitude and frequency references. Therefore, voltage-source inverter control methods are generally used, such as droop control and virtual synchronous machine control. In grid-connected operation, the main grid can provide a voltage reference. To achieve plug-and-play functionality for distributed renewable energy and seamless switching between grid-connected and off-grid modes, the two operation modes should use the same control strategy as much as possible.

[0004] However, traditional droop control lacks inertia and damping capabilities, and the system frequency and voltage still pose a significant risk of exceeding limits. Therefore, energy storage control systems employing traditional droop control cannot simultaneously meet the requirements of both operating modes.

[0005] This invention proposes a solution to improve the stability of source-grid-load-storage systems in both off-grid and grid-connected modes. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a grid-to-off-grid switching control method in a grid-to-grid energy storage system with end-connected series-parallel source-grid-load-storage structure.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] A method for grid-connected / off-grid switching control in a grid-connected energy storage system with end-point series-parallel connection of source, grid, load, and energy storage is provided.

[0009] The source-grid-load-storage system includes: distributed power sources, energy storage units, inverters, and AC loads; the distributed power sources and energy storage units are connected to the AC bus via inverters, the AC loads are connected to the AC bus, and the public power grid is connected to the AC bus via transformers and grid-connected switches; the grid-connected / off-grid switching control includes:

[0010] The instantaneous active power P output by the inverter e and reactive power Q e Used for virtual synchronous generator (VSG) control, enabling the source-grid-load-storage system to dampen system frequency changes in off-grid mode, and to dampen output and suppress power oscillations in grid-connected operation mode;

[0011] When switching the source-grid-load-storage system from off-grid operation to grid-connected operation, first determine whether the voltage amplitude difference Δu and phase difference Δθ between the inverter and the public grid simultaneously meet the preset grid connection conditions; if they meet, close the grid connection switch to connect the AC bus to the public grid; if they do not meet, adjust the voltage amplitude or phase output of the inverter until the grid connection conditions are met.

[0012] When switching from grid-connected operation to off-grid operation, disconnect the grid-connected switch and simultaneously set the reference active power P. ref Adjusting to 0 enables the switch from grid-connected to off-grid status.

[0013] As a preferred embodiment of the present invention, the distributed power source refers to at least one of photovoltaic or wind turbine power generation equipment.

[0014] In a preferred embodiment of the present invention, the inverter is a voltage-controlled inverter; the instantaneous active power P output by the inverter is calculated by detecting the output voltage and output current of the inverter. e and reactive power Q e Used for the control of virtual synchronous generators.

[0015] As a preferred embodiment of the present invention, during off-grid operation, the source-grid-load-storage system calculates the inverter output voltage reference phase θ to provide the inverter output voltage phase, and calculates the d-axis voltage reference value E for voltage and current dual closed-loop control; the specific calculation formula is as follows:

[0016]

[0017] In the formula, ω ref P is the power grid frequency; ref , P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia; s is the Laplace operator; D is the damping coefficient; U n This represents the effective value of the power grid.

[0018] As a preferred embodiment of the present invention, the switching of the source-grid-load-storage system from off-grid operation to grid-connected operation specifically includes:

[0019] (1) Detect the inverter grid connection point voltage V abc and public grid voltage V gabc The voltage phases of the two are obtained through a phase-locked loop; then, the phase comparison circuit determines whether the voltage amplitude difference Δu and phase difference Δθ between the inverter and the public grid meet the preset grid connection conditions.

[0020] (2) If the grid connection conditions are met, close the grid connection switch to connect the source, grid, load and storage to the public power grid;

[0021] If the voltage amplitude difference does not meet the grid connection conditions, a voltage amplitude adjustment signal k is generated through the amplitude and phase synchronization unit. n Δu, and add it to the inverter d-axis voltage reference value E;

[0022] If the phase difference does not meet the grid connection conditions, a voltage phase adjustment signal k is generated through the amplitude and phase synchronization unit. m Δθ is added to the inverter output voltage reference phase θ until the grid connection conditions are met.

[0023] The specific calculation formula is as follows:

[0024]

[0025] In the formula, ω ref P is the power grid frequency; ref , P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia; s is the Laplace operator; D is the damping coefficient; U n For the effective value of the power grid; k m Δθ is the phase control adjustment signal, k n Δu is the amplitude control adjustment signal.

[0026] The present invention further provides a computer device, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to perform the aforementioned grid-to-off-grid switching control method in a terminal serial-parallel type source-grid-load-storage grid-based energy storage system.

[0027] The present invention further provides a computer-readable storage medium storing computer instructions for causing the computer to execute the aforementioned grid-to-off-grid switching control method in a terminal series-parallel type source-grid-load-storage grid-based energy storage system.

[0028] This invention also provides a system for end-point series-parallel source-grid-load-storage grid-connected energy storage through grid-connected / off-grid switching control. The system includes a source-grid-load-storage system and a microgrid controller. The microgrid controller is connected to the distributed power source, energy storage unit, inverter, and AC load in the source-grid-load-storage system via a switch and communication lines, respectively. The microgrid controller is connected to monitoring equipment via a communication line for human-machine interaction. The microgrid controller includes at least one processor and a memory communicatively connected to the at least one processor. The memory stores instructions that are executed by the at least one processor. The instructions are executed by the at least one processor to cause the at least one processor to perform the aforementioned grid-connected / off-grid switching control method in the end-point series-parallel source-grid-load-storage grid-connected energy storage system.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention enables the end-point energy storage system to have good dynamic and steady-state performance under grid connection and off-grid switching, and can meet the requirements of both operating modes.

[0031] 2. By setting up a process to pre-detect whether the grid connection conditions are met, the present invention can ensure that the mode switching process can be carried out smoothly, thereby improving the flexibility and stability of the on-grid and off-grid switching of the end-point energy storage system. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the grid-to-off-grid switching control device for realizing the end-to-end series-parallel type source-grid-load-storage energy storage structure in this invention.

[0033] Figure 2 This is a control principle diagram of the inverter of the present invention.

[0034] Figure 3 This is a schematic diagram of the inverter control principle after conversion when connected to the grid according to the present invention.

[0035] Figure 4 This is a flowchart illustrating the principle of grid-connected / off-grid switching in this invention.

[0036] Figure 5 This is a Simulink simulation diagram of the switching from off-grid operation to grid-connected operation in this invention.

[0037] Figure 6 This is a Simulink simulation diagram of the switching from grid-connected operation to off-grid operation in this invention. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0039] Part 1: Source-Grid-Load-Storage Energy Storage System

[0040] Figure 1As an example, this paper demonstrates a system for end-point series-parallel source-grid-load-storage energy storage through grid-connected switching control. The dashed box in the figure represents the source-grid-load-storage system described in this invention, including distributed power sources (photovoltaics, wind power, etc.), energy storage units, inverters (DC-AC converters), and AC loads. The distributed power sources and energy storage units are connected to the AC bus via the inverter, the AC load is connected to the AC bus, and the public power grid is connected to the AC bus via a transformer and a grid-connected switch. The inverter is a voltage-controlled inverter, and the operation control of the energy storage system includes control of the inverter and the grid-connected switch.

[0041] In this example, the 35kV public grid uses a transformer to convert high-voltage electricity to a voltage level suitable for energy storage / microgrid (i.e., the source-grid-load-storage method described in this invention), serving as the transformer interface between the high-voltage grid and the microgrid. At the interface of another 10kV public grid (or another voltage level outlet of the microgrid), a transformer is used to achieve voltage conversion on the low-voltage side (0.4kV) of the microgrid. In the source-grid-load-storage method (within the dashed box), the series-parallel grid-connected energy storage device includes two converters (AC / DC, DC / AC) + a 200kWh energy storage unit (such as a lithium battery), used to smooth out output fluctuations of photovoltaic / wind turbines, charge during off-peak hours and discharge during peak hours, and ensure power supply stability when the microgrid is off-grid. Distributed power sources include photovoltaics and wind turbines, providing electricity to users as clean energy sources; AC loads are connected to the 0.4kV AC bus as the system's power load.

[0042] The PCC switch serves as the boundary between the microgrid and the external power grid, controlling whether the microgrid operates in grid-connected mode (interconnected with the grid) or off-grid mode (independent power supply). Communication cables transmit the operating status of the inverter, energy storage unit, photovoltaic system, wind turbine, and PCC switch to the switch, which then aggregates the data to the microgrid controller. The controller controls the PCC switch and related equipment via secondary cables and communication cables. The monitoring terminal displays the operating parameters of the entire system (voltage, power, etc.) and enables human-machine interaction. The entire system integrates new energy generation, energy storage, and load, flexibly switching operating modes through the PCC switch to utilize clean energy while ensuring power supply reliability.

[0043] Through the microgrid controller, this system can realize two core modes of operation: grid-connected operation and off-grid operation, based on grid-connected and off-grid switching control. Specific scenarios based on equipment characteristics are as follows:

[0044] I. Grid-connected operation mode (PCC switch closed)

[0045] The microgrid is connected to the external 35kV / 10kV power grid for coordinated power supply. Under normal grid-connected power supply mode, photovoltaic and wind turbines prioritize power generation for user needs; excess power can be fed back to the grid or used to charge energy storage devices; if power generation is insufficient, the grid supplements the supply. This maximizes the utilization of clean energy and reduces user electricity costs. Under grid-connected peak shaving and valley filling mode, during off-peak hours (low electricity prices), the generation, grid, load, and storage systems draw power from the grid / distributed power sources for charging; during peak hours (high electricity prices), the energy storage discharges in conjunction with power generation to supply users, reducing peak grid demand and lowering user electricity costs, while also assisting the grid in peak shaving. Under grid-connected standby support mode, the energy storage is in a "hot standby" state. If a photovoltaic / wind turbine experiences a sudden failure, the energy storage quickly discharges to replenish power, preventing power outages for users (the grid serves as the final backup), and improving power supply reliability.

[0046] II. Off-grid operation mode (PCC switch off)

[0047] The microgrid is isolated from the external power grid and supplies power independently. In off-grid stable power supply mode, photovoltaic and wind turbines generate electricity, and energy storage devices adjust their output in real time (charging when there is excess power generation and discharging when there is insufficient power generation) to directly supply power to users. During grid maintenance / faults, basic power supply for users is guaranteed (the combined capacity of power generation and energy storage must be greater than or equal to the user's load). In off-grid emergency supply mode, non-critical loads are prioritized for disconnection, and energy storage supplies power with "high priority," working in conjunction with photovoltaic / wind turbines to ensure power supply for critical users (such as important facilities). Emergency power supply is provided during prolonged grid failures.

[0048] Part Two: Implementation Method of Grid-Connected / Off-Grid Switching Control for Grid-Connected Energy Storage Systems

[0049] Based on the aforementioned grid-connected energy storage system, this invention utilizes the instantaneous active power P output by the inverter. e and reactive power Q e This technology is used for virtual synchronous generator (VSG) control, enabling the source-grid-load-storage system to dampen system frequency changes in off-grid mode and to provide damped output and suppress power oscillations in grid-connected operation mode. The virtual synchronous generator control refers to a control method that simulates the inertial and damping characteristics of a synchronous generator in power electronic equipment, based on the external characteristics of the generator.

[0050] 1. Off-network operation

[0051] First, by detecting the inverter output voltage V abc and output current i abc The instantaneous active power P output by the inverter is calculated. e and reactive power Q eThe inverter modulation wave is obtained through a virtual synchronous generator loop and a voltage-current closed loop to control the inverter. To ensure the energy storage unit has inertia and damping capabilities when connected to the grid, the inverter modulation wave is obtained through a virtual synchronous generator outer loop and a voltage-current closed loop for inverter control. The reactive power-voltage droop control is the same as traditional droop control. The inverter output voltage reference phase θ is obtained to provide the inverter output voltage phase, and the d-axis voltage reference value E is used for voltage and current dual closed-loop control. The specific calculation formula is as follows:

[0052]

[0053] In the formula, ω ref P is the power grid frequency; ref ,P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia; s is the Laplace operator; D is the damping coefficient; U n This represents the effective value of the power grid.

[0054] The control block diagram for off-grid operation is as follows: Figure 2 As shown, the specific explanation is as follows:

[0055] The core of the control of a virtual synchronous generator (VSG) is to simulate the rotor motion and electromagnetic characteristics of a traditional synchronous generator to achieve virtual inertia and damping control of the inverter, and finally to determine the reference phase and amplitude of the output voltage, thereby driving the inverter to operate in grid-connected or independently.

[0056] The upper part of the diagram represents the active power-frequency control loop (determining phase θ), which is the core of the synchronous generator rotor motion equations and is responsible for maintaining system frequency stability. The calculations include: calculating the acceleration power signal from the power deviation, which reflects the degree of active power imbalance in the system. The rotor motion simulation process fully simulates the dynamic response of the synchronous generator in terms of "torque-angular velocity-angle". J (virtual moment of inertia) determines the system's ability to resist frequency abrupt changes, while D (damping coefficient) is used to suppress frequency oscillations; together, they make the system frequency dynamics closer to that of a traditional synchronous machine. In the diagram, ω represents the system angular frequency.

[0057] The lower part of the diagram represents the reactive power-voltage control loop (lower section, determining the amplitude E). This part simulates the excitation regulation characteristics of a synchronous generator to maintain a stable output voltage amplitude. The calculations include: calculating the voltage correction amount from the reactive power deviation; synthesizing the voltage amplitude to obtain the d-axis voltage reference value E, which serves as the amplitude command for the subsequent voltage and current dual closed loop.

[0058] In dual-loop control, phase θ and amplitude E are used as references. The voltage and current dual-loop control is responsible for accurately tracking commands, achieving rapid and stable regulation of the inverter output voltage. The coordinate transformation (dq / abc) transforms the voltage reference values ​​Ud and Uq in the rotating coordinate system into reference voltages in the three-phase stationary coordinate system, ultimately generating PWM drive signals to control the inverter switching action.

[0059] This control strategy, by "simulating the electromechanical transient characteristics of a synchronous generator," enables the inverter to possess virtual inertia and damping capabilities, thus solving the problems of insufficient inertia and poor frequency stability in power electronic systems.

[0060] 2. Grid-connected operation

[0061] Since voltage-controlled inverters appear as voltage sources externally, their voltages need to be synchronized with the public power grid before connection to avoid power surges during grid connection. Therefore, when switching from off-grid to grid-connected operation, the inverter's grid connection point voltage V needs to be detected first. abc and public grid voltage V gabc The voltage phases of the two are obtained through a phase-locked loop. Then, a phase comparison circuit is used to determine whether the voltage amplitude difference Δu and phase difference Δθ between the inverter and the public grid meet the grid connection conditions. The grid connection conditions can be freely set according to specific requirements.

[0062] If the amplitude difference does not meet the grid connection conditions, a voltage amplitude adjustment signal k is generated through the amplitude and phase synchronization unit. n Δu is added to the inverter reference value. If the phase difference does not meet the grid connection conditions, a voltage phase adjustment signal k is generated through the amplitude phase synchronization unit. m Δθ is added to the inverter reference value.

[0063] At this point, the calculation formulas for the inverter output voltage reference angular frequency θ and the d-axis voltage reference value E are adjusted accordingly:

[0064]

[0065] In the formula, ω ref P is the power grid frequency; ref ,P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia; s is the Laplace operator; D is the damping coefficient; U n For the effective value of the power grid; k m Δθ is the phase control adjustment signal, k n Δu is the amplitude control adjustment signal.

[0066] k m The angular disturbance coefficient represents the tracking speed between the inverter's output phase angle and the grid phase angle; k n The voltage disturbance coefficients represent the tracking speed between the inverter's output voltage and the grid voltage. These two coefficients can be obtained through theoretical derivation, simulation fitting, or experimental identification, and are considered publicly available prior art.

[0067] The control block diagram for grid-connected operation is as follows: Figure 3 As shown.

[0068] and Figure 2 Compared to the control block diagram shown in the off-grid operation state, in Figure 3 Two additional perturbation inputs were added. These include: an angle perturbation, and a k-perturbation added before the integral term 1 / s. m The input Δθ is the disturbance caused by the angle deviation; the voltage disturbance is caused by the addition of k in the generation stage of the voltage amplitude E. n The input Δu represents the disturbance caused by voltage deviation. These two newly added disturbance terms take into account the effects of angle and voltage fluctuations, making the control process closer to the actual system. The addition of phase and voltage compensation components improves the system's stability and dynamic performance under complex operating conditions.

[0069] 2. On-grid / off-grid switching control

[0070] Based on the above adjustments to the calculation formulas for the inverter output voltage reference angular frequency θ and the d-axis voltage reference value E under grid-connected operation, this invention enables the source-grid-load-storage system to have damping capability against system frequency changes in off-grid mode, and to have damped output and power oscillation suppression capability in grid-connected operation mode. Furthermore, based on the aforementioned adjustments to the calculation formulas under different operating conditions, this invention further proposes corresponding switching control strategies, as follows:

[0071] (1) When switching the source-grid-load-storage system from off-grid operation to grid-connected operation, first determine whether the voltage amplitude difference Δu and phase difference Δθ between the inverter and the public grid simultaneously meet the preset grid connection conditions; if they meet, close the grid connection switch to connect the AC bus to the public grid; if they do not meet, adjust the voltage amplitude or phase output of the inverter until the grid connection conditions are met.

[0072] (2) When switching the source-grid-load-storage system from grid-connected operation to off-grid operation, disconnect the grid-connected switch and simultaneously change the reference active power P. ref Adjusting to 0 enables the switch from grid-connected to off-grid status.

[0073] like Figure 4As shown, this invention is based on the core control architecture of microgrids and distributed power grid connection, and realizes seamless switching between two modes of inverter operation: independent operation (off-grid) and grid-connected operation (grid-connected).

[0074] First, the control of the virtual synchronous generator (VSG) is the core of the entire system. It is responsible for simulating the electromechanical characteristics of a synchronous generator, providing amplitude and phase commands for the subsequent voltage and current dual closed loop, and enabling the inverter to have virtual inertia and damping characteristics.

[0075] When the system needs to be connected to the power grid, smooth synchronization and switching are achieved. The pre-synchronization stage involves acquiring the grid voltage V. gabc With inverter output voltage V abc The voltage amplitude difference Δu and phase difference Δθ are compared and calculated. The difference is then converted into a compensation signal k using an amplitude and phase synchronization unit. m Δu and k n Δθ is superimposed on the output of the VSG outer loop to gradually eliminate the voltage amplitude and phase difference. When Δu and Δθ meet the grid connection threshold, the grid connection switch is triggered to close.

[0076] After grid connection, the VSG outer loop operates in coordination with the grid, participating in frequency and voltage regulation. The dual-closed-loop control uses the θ and E outputs of the VSG outer loop, along with the grid compensation signal, as references. Through voltage and current loops, it achieves precise tracking of the inverter output, ensuring dynamic response speed and steady-state accuracy of the output voltage. The voltage command in the rotating coordinate system is converted into a reference signal in the three-phase stationary coordinate system, ultimately generating PWM drive pulses to control the inverter's switching action.

[0077] When the off-grid command is issued, the grid connection switch is disconnected. The active power reference value P is forcibly set. ref =0, independently adjusting the amplitude and phase of the output voltage based solely on the power demand of the local load. When the system is in off-grid mode, the voltage and frequency of the local load are maintained stable through virtual synchronous generator (VSG) control.

[0078] Based on the above innovative design, this invention is significantly different from existing switching control strategies: (1) This invention can achieve seamless dual-mode switching: the off-grid / grid-connected mode transition is achieved through the pre-synchronization link, avoiding current surges and voltage fluctuations during the switching process. (2) This invention provides virtual inertia support: the VSG outer loop simulates the inertia and damping of the synchronous generator, improving the anti-disturbance capability and frequency stability of the power electronic system. (3) This invention constructs a hierarchical control architecture: mode switching, characteristic simulation, and power regulation are implemented in layers, with clear logic, making it easy to debug and expand.

[0079] Figure 5 , 6Figure 5 shows Simulink simulation diagrams of the proposed control strategy switching from off-grid to grid-connected operation and from grid-connected to off-grid operation. The local load is 10kW, the grid-connected power is 10kW, and the effective value of the three-phase grid voltage is 220V. Figure 5 shows that during system operation times t=0 seconds to t=0.5 seconds and t=0.5 seconds to t=1 seconds, the system switches from off-grid to grid-connected operation. At this time, the simulation diagram shows that the grid-connected current satisfies the inertial element of VSG control, exhibiting voltage source characteristics, and the local load maintains a constant continuous operating current, while the inverter output voltage remains basically stable. Figure 6 shows that during system operation times t=0 seconds to t=0.5 seconds and t=0.5 seconds to t=1 seconds, the system switches from grid-connected to off-grid operation. At this time, the simulation diagram shows that the grid-connected current drops from full load to 0, and the local load current maintains a constant continuous operating current, while the inverter output voltage remains basically stable. Therefore, the effectiveness of the proposed control strategy is verified.

[0080] Based on the aforementioned innovative grid-connected / off-grid switching control method, this invention further provides a computer device, comprising: at least one processor and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executed by the at least one processor, the instructions being executed by the at least one processor to cause the at least one processor to execute the aforementioned grid-connected / off-grid switching control method in a terminal series-parallel type source-grid-load-storage grid-based energy storage system. It is understood that a microgrid controller can be a suitable computer device.

[0081] In addition, the present invention provides a computer-readable storage medium storing computer instructions for causing the computer to execute the aforementioned grid-to-off-grid switching control method in a terminal series-parallel source-grid-load-storage grid-based energy storage system.

[0082] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for grid-to-off-grid switching control in a terminal series-parallel type source-grid-load-storage energy storage system, characterized in that, The source-grid-load-storage system includes: distributed power sources, energy storage units, inverters, and AC loads; the distributed power sources and energy storage units are connected to the AC bus via inverters, the AC loads are connected to the AC bus, and the public power grid is connected to the AC bus via transformers and grid-connected switches; the grid-connected / off-grid switching control includes: The instantaneous active power P output by the inverter e and reactive power Q e Used for virtual synchronous generator (VSG) control, enabling the source-grid-load-storage system to dampen system frequency changes in off-grid mode, and to dampen output and suppress power oscillations in grid-connected operation mode; When switching the source-grid-load-storage system from off-grid operation to grid-connected operation, first determine whether the voltage amplitude difference Δu and phase difference Δθ between the inverter and the public grid simultaneously meet the preset grid connection conditions; if they meet, close the grid connection switch to connect the AC bus to the public grid; if they do not meet, adjust the voltage amplitude or phase output of the inverter until the grid connection conditions are met. When switching from grid-connected operation to off-grid operation, disconnect the grid-connected switch and simultaneously set the reference active power P. ref Adjusting to 0 enables the switch from grid-connected to off-grid status.

2. The method according to claim 1, characterized in that, The distributed power source refers to at least one of photovoltaic or wind turbine power generation equipment.

3. The method according to claim 1, characterized in that, The inverter is a voltage-controlled inverter; by detecting the inverter's output voltage and output current, the instantaneous active power P output by the inverter is calculated. e and reactive power Q e Used for the control of virtual synchronous generators.

4. The method according to claim 1, characterized in that, During off-grid operation, the source-grid-load-storage system calculates the inverter output voltage reference phase θ to provide the inverter output voltage phase, and calculates the d-axis voltage reference value E for voltage and current dual closed-loop control; the specific calculation formulas are as follows: ； In the formula, ω ref P is the power grid frequency; ref , P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia. s is the Laplace operator; D is the damping coefficient; U n This represents the effective value of the power grid.

5. The method according to claim 1, characterized in that, When switching the source-grid-load-storage system from off-grid operation to grid-connected operation, the specific steps include: (1) Detect the inverter grid connection point voltage V abc and public grid voltage V gabc The voltage phases of the two are obtained through a phase-locked loop; then, the phase comparison circuit determines whether the voltage amplitude difference ∆u and phase difference ∆θ between the inverter and the public grid meet the preset grid connection conditions. (2) If the grid connection conditions are met, close the grid connection switch to connect the source, grid, load and storage to the public power grid; If the voltage amplitude difference does not meet the grid connection conditions, a voltage amplitude adjustment signal k is generated through the amplitude and phase synchronization unit. n Δu, and add it to the inverter d-axis voltage reference value E; If the phase difference does not meet the grid connection conditions, a voltage phase adjustment signal k is generated through the amplitude and phase synchronization unit. m Δθ is added to the inverter output voltage reference phase θ until the grid connection conditions are met. The specific calculation formula is as follows: ； In the formula, ω ref P is the power grid frequency; ref , P e These are the reference active power and the calculated active power of the inverter, respectively; Q ref Q e These represent the reference reactive power and the calculated reactive power of the inverter, respectively; m and n are the droop coefficients; J is the moment of inertia; s is the Laplace operator; D is the damping coefficient; U n For the effective value of the power grid; k m Δθ is the phase control adjustment signal, k n Δu is the amplitude control adjustment signal.

6. A computer device, characterized in that, include: At least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions that are executed by the at least one processor to cause the at least one processor to perform the grid-connected / off-grid switching control method in a grid-connected energy storage system according to any one of claims 1 to 5.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions, which are used to cause the computer to execute the grid-connected / off-grid switching control method in the end-to-end series-parallel source-grid-load-storage grid energy storage structure as described in any one of claims 1 to 5.

8. A system for end-point series-parallel type source-grid-load-storage grid-based energy storage through grid-connected / off-grid switching control, characterized in that, The system includes a source-grid-load-storage (PGS-S) configuration and a microgrid controller. The latter connects to the distributed power sources, energy storage units, inverters, and AC loads in the PPS-S configuration via switches and communication lines. The microgrid controller is connected to monitoring equipment via communication lines for human-machine interaction. The microgrid controller includes at least one processor and a memory communicatively connected to the at least one processor. The memory stores instructions that are executed by the at least one processor. The instructions are executed by the at least one processor to cause the at least one processor to perform the grid-connected / off-grid switching control method in the end-to-end series-parallel PPS-S configuration as described in any one of claims 1 to 5.

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