A microgrid off-grid to grid-connected control method and system based on photovoltaic storage and charging

Abstract

The present invention provides a control method and system for off-grid to grid-connected microgrid based on photovoltaic storage and charging. The method is based on a circuit breaker and a contactor connected in series between the grid side and the microgrid side. The method includes: confirming whether the opening state of the circuit breaker is normal according to the off-grid to grid-connected instruction, and controlling the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; collecting the voltage and current on the grid side and the microgrid side to determine whether the microgrid side and the grid side have synchronization conditions, and if they have synchronization conditions, controlling the microgrid side contactor to close. The present invention effectively avoids the disturbance problem caused to the grid when switching from off-grid to grid-connected, and no longer requires PCS to complete status monitoring and closing work at the millisecond level, which greatly reduces the difficulty of implementing off-grid to grid-connected, and can also reduce the equipment cost of the entire system.

Description

Technical Field

[0001] The present invention relates to the field of electric power grids, and more specifically, to a method and system for controlling off-grid and grid-connected microgrids based on photovoltaic storage and charging. Background Art

[0002] With the development of society and the advancement of science and technology, the fields of power system engineering, smart grid technology and energy storage system technology have received extensive attention and research. As an emerging power system, microgrid can achieve self-sufficiency in electricity and improve the stability and reliability of the power system to a certain extent. Microgrids are usually composed of distributed power sources, energy storage systems and loads. Distributed power sources include renewable energy such as solar energy, wind energy, geothermal energy, etc., and energy storage systems mainly include batteries and supercapacitors.

[0003] The existing microgrid on-grid and off-grid related control technologies mainly include strategies such as planned on-grid to off-grid, unplanned on-grid to off-grid, off-grid to on-grid, on-grid operation and off-grid operation. The operation mode of the microgrid is switched manually or automatically to achieve stable operation of the microgrid. In the on-grid mode, the microgrid can interact with the large grid through functions such as anti-reverse flow, demand control and surplus power access to the grid. In the off-grid mode, the microgrid needs to have the protection function of the SOC (state of charge) of the energy storage battery and cut off non-critical loads to ensure the safe operation of the energy storage system. In the process of planned on-grid to off-grid, it is necessary to reduce the impact of the current when the gate is disconnected and control the power balance inside the microgrid. In the process of unplanned on-grid to off-grid, the PCS (Power Conversion System, bidirectional energy storage converter) uses millisecond-level island state monitoring to ensure the normal progress of unplanned on-grid to off-grid. During the off-grid transition to grid-connected mode, after the three-phase voltage and frequency on the large grid side return to normal, after the EMS (energy management system) receives the command to switch the mode, the EMS sends the real-time information such as the amplitude difference, phase difference, and frequency difference between the microgrid side and the grid side to the PCS through the Goose communication method, and the PCS main power supply is responsible for adjusting the bus voltage in the microgrid to synchronously track the voltage on the large grid side; the EMS determines in real time whether the synchronous closing conditions are met. If the synchronous conditions are met within the preset time of starting the mode switch, the EMS controls the static switch of the PCC point (Point of Common Coupling) to close, and controls the PCS mode to switch from VF to PQ, and the microgrid operation state is switched to the grid-connected operation state.

[0004] Although the existing microgrid on-grid and off-grid control technology can achieve stable operation of microgrids, there are still some problems and limitations. The existing microgrid control technology may cause power fluctuations and voltage fluctuations during the switching process between on-grid and off-grid modes, affecting the quality and stability of electricity. In the process of switching from off-grid to on-grid, it is first necessary to use Goose communication with extremely fast communication rate and achieve disturbance-free switching. The PCS needs to quickly adjust the phase to reduce interference with the power grid, which is extremely difficult to achieve and has very high performance requirements for the PCS.

[0005] Therefore, it is necessary to study a more reliable microgrid off-grid to grid-connected control strategy based on photovoltaic storage and charging. Summary of the invention

[0006] In view of the technical problems existing in the prior art, the present invention provides a microgrid off-grid to grid-connected control method and system based on photovoltaic storage and charging, which realizes disturbance-free switching when switching from off-grid to grid-connected and improves power stability.

[0007] According to a first aspect of the present invention, a method for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging is provided, based on a circuit breaker and a contactor arranged in series between the grid side and the microgrid side, comprising: According to the off-grid to grid-connected instruction, confirm whether the circuit breaker's opening state is normal, and control the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; The voltage and current of the grid side and the microgrid side are collected to determine whether the microgrid side and the grid side meet the synchronization conditions. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0008] Based on the above technical solution, the present invention can also make the following improvements.

[0009] Optionally, the confirming whether the opening state of the circuit breaker is normal according to the off-grid to grid-connected instruction includes: Detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side; If the zero drift value of the grid-connected point circuit breaker is within a preset range, it is determined that the grid-connected point circuit breaker opening state is normal; otherwise, it is determined that the grid-connected point circuit breaker opening state is abnormal.

[0010] Optionally, collecting the voltage and current of the grid side and the microgrid side to determine whether the microgrid side and the grid side meet the synchronization condition includes: Collect the voltage and current on the grid side and microgrid side respectively; According to the collected voltages and currents on the grid side and the microgrid side, the amplitude, phase, and frequency of the grid side voltage and the amplitude, phase, and frequency of the microgrid side voltage are extracted respectively; Calculate the amplitude difference, phase difference and frequency difference between the grid-side voltage and the microgrid-side voltage; Based on the calculated amplitude difference, phase difference and frequency difference, it is determined whether the grid side and the microgrid side meet the synchronization conditions.

[0011] Optionally, the collecting the voltage and current on the grid side and the microgrid side respectively includes: By collecting the voltage and current at both ends of the contactor, the voltage and current on the grid side and the microgrid side are obtained.

[0012] Optionally, judging whether the grid side and the microgrid side meet the synchronization conditions according to the calculated amplitude difference, phase difference, and frequency difference includes: If the phase sequence of the grid side and the microgrid side is the same according to the calculated phase difference between the grid side and the microgrid side, and the phase difference, amplitude difference and frequency difference between the grid side and the microgrid side are within the preset range, then it is determined that the grid side and the microgrid side meet the synchronization conditions; Otherwise, it is determined that the grid side and the microgrid side do not meet the synchronization conditions.

[0013] According to a second aspect of the present invention, a microgrid off-grid to grid-connected control system based on photovoltaic storage and charging is provided, comprising an EMS controller and a PCS, wherein: The EMS controller is used to confirm whether the opening state of the circuit breaker is normal according to the monitoring data of the PCS when the off-grid to grid-connected instruction is detected in real time. When the opening state is confirmed to be normal, the circuit breaker at the grid-connected point is controlled to close and the off-grid to grid-connected instruction is sent to the PCS; PCS is used to monitor the voltage and current at both ends of the microgrid contactor in real time, and judge whether the microgrid side and the grid side meet the synchronization conditions based on the collected voltage and current. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0014] Optionally, the EMS controller sends an off-grid to on-grid switching instruction to the PCS via modbus TCP communication.

[0015] Optionally, the PCS includes a zero drift detection module, and the EMS controller includes a state judgment module, wherein: The zero drift detection module is used to detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side; The state judgment module is used to judge whether the zero drift value of the grid-connected point circuit breaker is within a preset range. If the zero drift value of the grid-connected point circuit breaker is within the preset range, it is judged that the grid-connected point circuit breaker opening state is normal; otherwise, it is judged that the grid-connected point circuit breaker opening state is abnormal.

[0016] Optionally, the PCS further includes a voltage / current detection module, a parameter operation module and a synchronization condition judgment module, wherein: The voltage / current detection module is used to collect the voltage and current of the grid side and the microgrid side respectively; The parameter operation module is used to extract the amplitude, phase, and frequency of the grid-side voltage and the amplitude, phase, and frequency of the microgrid-side voltage respectively according to the collected voltage and current on the grid-side and microgrid-side; and is also used to calculate the amplitude difference, phase difference, and frequency difference between the grid-side voltage and the microgrid-side voltage; The synchronization condition judgment module is used to judge whether the grid side and the microgrid side meet the synchronization conditions based on the calculated amplitude difference, phase difference, and frequency difference.

[0017] Optionally, the synchronization condition judgment module includes a phase sequence judgment submodule, a phase difference judgment submodule, an amplitude judgment submodule, a frequency judgment submodule and a synchronization comprehensive judgment submodule, wherein: The phase sequence judgment submodule is used to judge whether the phase sequence of the grid side and the microgrid side is the same according to the phase difference between the grid side and the microgrid side; The phase difference judgment submodule is used to judge whether the phase difference between the grid side and the microgrid side is within a preset phase difference range; The amplitude judgment submodule is used to judge whether the amplitude difference between the grid side and the microgrid side is within a preset amplitude difference range; The frequency determination submodule is used to determine whether the frequency difference between the grid side and the microgrid side is within a preset frequency difference range; The synchronization comprehensive judgment submodule is used to determine that the grid side and the microgrid side meet the synchronization conditions when the phase sequence of the grid side and the microgrid side is the same, the phase difference is within a preset phase difference range, the amplitude difference is within a preset amplitude difference range, and the frequency difference is within a preset frequency difference range.

[0018] According to a third aspect of the present invention, there is provided an electronic device comprising a memory and a processor, wherein the processor is used to implement the steps of the above-mentioned off-grid to grid-connected control method of a microgrid based on photovoltaic storage and charging when executing a computer management program stored in the memory.

[0019] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium having a computer management program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned method for controlling off-grid to grid-connected microgrid based on photovoltaic storage and charging.

[0020] The present invention provides a method, system, electronic device and storage medium for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging, which has the following beneficial effects: (1) The microgrid control technology of the present invention can effectively avoid power fluctuations and voltage fluctuations caused to the power grid during off-grid to grid-connected control by proposing a new control strategy, thereby improving the quality and stability of power transmission.

[0021] (2) The present invention proposes that the PCS collects the voltage and current at both ends of the contactor to characterize the voltage and current on the grid side and the microgrid side. By controlling the grid-connected point circuit breaker and the microgrid-side contactor to close separately, the microgrid system can have better adaptability and no longer require the PCS to complete status monitoring and closing work in milliseconds. This greatly reduces the difficulty of off-grid to grid-connected operation and can also reduce the equipment cost of the entire power system. It has better usability and stability in system debugging and power product transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of an application scenario of a microgrid planned off-grid and grid-connected based on photovoltaic storage and charging provided by the present invention; Figure 2 A flow chart of a method for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging provided by an embodiment of the present invention; Figure 3 A block diagram of a microgrid off-grid to grid-connected control system based on photovoltaic storage and charging provided in an embodiment of the present invention; Figure 4 A schematic diagram of the hardware structure of a possible electronic device provided by the present invention; Figure 5 A schematic diagram of the hardware structure of a possible computer-readable storage medium provided by the present invention. DETAILED DESCRIPTION

[0023] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0024] Figure 1 A schematic diagram of an application scenario of a microgrid planned off-grid and grid-connected based on photovoltaic storage and charging provided by an embodiment of the present invention, Figure 2 The present invention provides a flow chart of a method for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging. Figure 1 As shown, a circuit breaker and a contactor are arranged in series between the grid side and the microgrid side, the circuit breaker is close to the grid side, and the contactor is close to the microgrid side. Figure 1 In the process, the EMS controller is connected through hard-wired DO and controls the opening and closing of the circuit breaker. The PCS runs and monitors the voltage / current at the upper and lower ends of the contactor in real time. The EMS controller communicates with the PCS through the Modbus TCP protocol.

[0025] like Figure 2 As shown, this embodiment provides a microgrid off-grid to grid-connected control method based on photovoltaic storage and charging, the method comprising: S1, receiving the off-grid to grid-connected command, confirming whether the opening state of the circuit breaker is normal according to the off-grid to grid-connected command, and controlling the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; S2, collecting the voltage and current on the grid side and the microgrid side to determine whether the microgrid side and the grid side meet the synchronization conditions. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0026] It is understandable that, based on the defects in the background technology, the embodiment of the present invention proposes a control method for off-grid to grid-connected microgrid based on photovoltaic storage and charging. When the microgrid is in an off-grid operating state, first determine whether the open state of the circuit breaker at the grid connection point is normal, and then control the circuit breaker to close. At this time, the grid side and the microgrid side are only isolated by the contactor; then determine whether the microgrid side and the grid side at both ends of the contactor meet the synchronization conditions, and only close the contactor and connect the microgrid side to the grid when the synchronization conditions are met. Through the technical solution of this embodiment, the disturbance problem caused to the power grid during off-grid to grid connection is effectively avoided, and the PCS is no longer required to complete status monitoring and closing work at the millisecond level, which greatly reduces the difficulty of implementing off-grid to grid connection, and can also reduce the equipment cost of the entire system.

[0027] In a possible implementation manner, in step S1, confirming whether the opening state between the circuit breaker and the contactor is normal according to the off-grid switching instruction includes: Detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side; If the zero drift value of the grid-connected point circuit breaker is within a preset range, it is determined that the grid-connected point circuit breaker opening state is normal; otherwise, it is determined that the grid-connected point circuit breaker opening state is abnormal.

[0028] It is understandable that the corresponding Figure 1 In the scenario shown, that is, when the circuit breaker is disconnected, if the zero drift value of the voltage at the lower end of the circuit breaker is within the normal range, it means that the circuit breaker is normally opened, and the off-grid to grid-connected instruction can be executed at this time.

[0029] In a possible implementation manner, in step S2, collecting the voltage and current of the grid side and the microgrid side to determine whether the microgrid side and the grid side meet the synchronization condition includes: S201, respectively collecting the voltage and current on the grid side and the microgrid side; more specifically, obtaining the voltage and current on the grid side and the microgrid side by collecting the voltage and current at both ends of the contactor; S202, extracting the amplitude, phase, and frequency of the grid-side voltage and the amplitude, phase, and frequency of the microgrid-side voltage respectively according to the collected voltages and currents on the grid-side and microgrid-side; Calculate the amplitude difference, phase difference and frequency difference between the grid-side voltage and the microgrid-side voltage; S203, judging whether the grid side and the microgrid side meet the synchronization conditions based on the calculated amplitude difference, phase difference, and frequency difference. Specifically including: If the phase sequence of the grid side and the microgrid side is the same according to the calculated phase difference between the grid side and the microgrid side, and the phase difference, amplitude difference and frequency difference between the grid side and the microgrid side are within the preset range, then it is determined that the grid side and the microgrid side meet the synchronization conditions; Otherwise, it is determined that the grid side and the microgrid side do not meet the synchronization conditions.

[0030] It is understandable that the three conditions for the simultaneous parallel connection of power grids mainly include: 1. The phase sequence of the two power grids to be connected in parallel must be the same; 2. The frequencies of the two grids to be connected in parallel must be the same, or the frequency difference must be within the allowable range; 3. The voltages of the two grids to be connected in parallel must be equal, or the voltage difference must be within the allowable range.

[0031] In addition to the above three conditions, you should also pay attention to the following when performing synchronous parallel operations: The closing operation should be performed when the phase difference is zero to avoid inrush current.

[0032] Therefore, the synchronization comprehensive judgment submodule allows the contactor to close only when it determines that the grid side and the microgrid side meet the synchronization conditions through the above four conditions to ensure the safety of system operation.

[0033] Figure 3 A structure diagram of a microgrid off-grid to grid-connected control system based on photovoltaic storage and charging provided in an embodiment of the present invention, such as combined with Figure 1 and Figure 3 As shown, a microgrid off-grid to grid-connected control system based on photovoltaic storage and charging includes an EMS controller and a PCS, wherein: The EMS controller is used to monitor external instructions in real time. When an off-grid to grid-connected instruction is detected in real time, it confirms whether the opening state of the circuit breaker is normal according to the monitoring data of the PCS. When the opening state is confirmed to be normal, the circuit breaker at the grid-connected point is closed through the hard-wired DO, and the off-grid to grid-connected instruction is sent to the PCS; PCS is used to monitor the voltage and current at both ends of the contactor on the microgrid side by real-time monitoring of the electrical parameters at both ends of the contactor. It determines whether the microgrid side and the grid side meet the synchronization conditions based on the collected voltage and current. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0034] It can be understood that the off-grid to grid-connected control system of a microgrid based on photovoltaic storage and charging provided by the present invention corresponds to the off-grid to grid-connected control method of a microgrid based on photovoltaic storage and charging provided by the aforementioned embodiments. The relevant technical features of the off-grid to grid-connected control system of a microgrid based on photovoltaic storage and charging can refer to the relevant technical features of the off-grid to grid-connected control method of a microgrid based on photovoltaic storage and charging, which will not be repeated here.

[0035] In a possible implementation manner, after the EMS controller controls the grid-connected point circuit breaker to close via the hard-wired DO, the EMS controller sends an off-grid to grid-connected instruction to the PCS via the modbus TCP communication method.

[0036] In a possible embodiment, combining Figure 1 and Figure 3 As shown, the PCS includes a zero drift detection module, and the EMS controller includes a state judgment module, wherein: The zero drift detection module is used to detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side. It can be understood that the zero drift detection is to detect the phenomenon that the voltage at the output end deviates from the initial value and drifts up and down when the circuit is in an open circuit and there is no analog input. Figure 1 The application scenario shown is to detect the voltage zero drift value at the lower end of the circuit breaker when the circuit breaker is in the open state. Since the lower end of the circuit breaker and the upper end of the contactor are in a short-circuited state, the voltage zero drift value at the lower end of the circuit breaker is detected. Figure 1 This zero drift value can also be detected at the upper end of the contactor shown.

[0037] The state judgment module is used to judge whether the zero drift value of the grid-connected point circuit breaker is within a preset range. If the zero drift value of the grid-connected point circuit breaker is within the preset range, it is judged that the grid-connected point circuit breaker opening state is normal; otherwise, it is judged that the grid-connected point circuit breaker opening state is abnormal.

[0038] In a possible embodiment, Figure 3 As shown, the PCS also includes a voltage / current detection module, a parameter operation module and a synchronization condition judgment module, wherein: The voltage / current detection module is used to collect the voltage and current on the grid side and the microgrid side respectively; it can be understood that Figure 3 After the circuit breaker shown is closed, the voltage and current at the upper and lower ends of the contactor are detected, which can be used as the voltage and current on the grid side and the microgrid side; The parameter operation module is used to extract the amplitude, phase, and frequency of the grid-side voltage and the amplitude, phase, and frequency of the microgrid-side voltage respectively according to the collected voltage and current on the grid-side and microgrid-side; it is also used to calculate the amplitude difference, phase difference, and frequency difference between the grid-side voltage and the microgrid-side voltage; it can be understood that by subtracting the parameters on the grid-side and the microgrid-side, the difference of the parameters at both ends can be obtained for subsequent calculations; The synchronization condition judgment module is used to judge whether the grid side and the microgrid side meet the synchronization conditions based on the calculated amplitude difference, phase difference, and frequency difference.

[0039] In a possible implementation manner, the synchronization condition judgment module includes a phase sequence judgment submodule, a phase difference judgment submodule, an amplitude judgment submodule, a frequency judgment submodule and a synchronization comprehensive judgment submodule, wherein: The phase sequence judgment submodule is used to judge whether the phase sequence of the grid side and the microgrid side is the same according to the phase difference between the grid side and the microgrid side; The phase difference judgment submodule is used to judge whether the phase difference between the grid side and the microgrid side is within a preset phase difference range; The amplitude judgment submodule is used to judge whether the amplitude difference between the grid side and the microgrid side is within a preset amplitude difference range; The frequency determination submodule is used to determine whether the frequency difference between the grid side and the microgrid side is within a preset frequency difference range; The synchronization comprehensive judgment submodule is used to determine that the grid side and the microgrid side meet the synchronization conditions when the phase sequence of the grid side and the microgrid side is the same, the phase difference is within a preset phase difference range, the amplitude difference is within a preset amplitude difference range, and the frequency difference is within a preset frequency difference range.

[0040] It is understandable that the three conditions for the simultaneous parallel connection of power grids mainly include: 1. The phase sequence of the two power grids to be connected in parallel must be the same; 2. The frequencies of the two grids to be connected in parallel must be the same, or the frequency difference must be within the allowable range; 3. The voltages of the two grids to be connected in parallel must be equal, or the voltage difference must be within the allowable range.

[0041] In addition to the above three conditions, you should also pay attention to the following when performing synchronous parallel operations: The closing operation should be performed when the phase difference is zero to avoid inrush current.

[0042] Therefore, the synchronization comprehensive judgment submodule allows the contactor to close only when it determines that the grid side and the microgrid side meet the synchronization conditions through the above four conditions to ensure the safety of system operation.

[0043] Now combined with Figure 1 A specific implementation scenario is used as an example to illustrate.

[0044] like Figure 1The figure shows a schematic diagram of an application scenario of a planned off-grid to grid connection of a microgrid based on photovoltaic storage and charging of the present invention. A microgrid system based on photovoltaic storage and charging is constructed, which includes a power grid, a photovoltaic system, an energy storage system, an energy management system and a local load. Among them, the power grid is a power grid system, which includes transmission lines, transformers, etc.; the energy storage system uses lithium battery energy storage with a capacity of 100kWh and a charging and discharging efficiency of 95%; the photovoltaic system uses polycrystalline silicon solar panels with a rated power of 100kW; the energy management system (EMS controller) uses SunGrow's LC100, and the communication protocol between it and the energy storage converter PCS uses the Modbus TCP protocol. The local load is a small factory with a peak power of 100kW.

[0045] When the microgrid is in off-grid operation, the PCS and EMS controllers work normally, the EMS controller runs and monitors external commands in real time, the PCS runs and monitors the electrical parameters (such as voltage and current) at the upper and lower ends of the contactor in real time, and the EMS controls the opening and closing of the circuit breaker through hard-wired DO. Since the circuit breaker and the contactor are connected in series, the zero drift detection result of the circuit breaker can also be obtained by detecting the electrical parameters at the upper end of the contactor when the circuit breaker is in the open state.

[0046] like Figure 2 The flowchart of FIG. 1 shows a control strategy for a microgrid planned off-grid to grid-connected based on photovoltaic storage and charging of the present invention. Figure 2 As shown, the PCS operates normally off-grid, monitors the voltage / current values ​​on the upper and lower sides of the contactor in real time, and calculates the voltage (amplitude) difference, frequency difference and phase difference on both sides. The EMS controller operates normally. When the EMS receives the external off-grid to grid command signal, it first determines that there is no voltage at the lower end of the circuit breaker and controls the circuit breaker to close through the hard-wired DO, and then sends the "off-grid to grid command signal" to the PCS through the modbusTCP communication method. The PCS continues to run, judging the phase difference, voltage amplitude difference and frequency difference between the upper and lower sides of the contactor. This control strategy uses a dead band frequency range of 49.95Hz~50.05Hz. When the phase difference and voltage amplitude difference meet the conditions, the synchronous closing operation is performed to close the contactor and complete the off-grid to grid control logic.

[0047] The above technical solution effectively avoids the disturbance of the power grid caused by off-grid switching and grid-connected switching, and no longer requires PCS to complete status monitoring and closing work at the millisecond level, which greatly reduces the difficulty of off-grid switching and grid-connected switching, and can also reduce the equipment cost of the entire system.

[0048] See also Figure 4 , Figure 4 Schematic diagram of an electronic device provided by an embodiment of the present invention. Figure 4As shown, an embodiment of the present invention provides an electronic device 400, including a memory 410, a processor 420, and a computer program 411 stored in the memory 410 and executable on the processor 420. When the processor 420 executes the computer program 411, the following steps are implemented: According to the off-grid to grid-connected instruction, confirm whether the circuit breaker's opening state is normal, and control the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; The voltage and current of the grid side and the microgrid side are collected to determine whether the microgrid side and the grid side meet the synchronization conditions. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0049] See also Figure 5 , Figure 5 Schematic diagram of an embodiment of a computer-readable storage medium provided by the present invention. Figure 5 As shown, this embodiment provides a computer-readable storage medium 500, on which a computer program 511 is stored. When the computer program 511 is executed by a processor, the following steps are implemented: According to the off-grid to grid-connected instruction, confirm whether the circuit breaker's opening state is normal, and control the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; The voltage and current of the grid side and the microgrid side are collected to determine whether the microgrid side and the grid side meet the synchronization conditions. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

[0050] The embodiments of the present invention provide a method, system, electronic device and storage medium for controlling off-grid and on-grid microgrid based on photovoltaic storage and charging, which have the following advantages: (1) The microgrid control technology of the present invention can effectively avoid power fluctuations and voltage fluctuations caused to the power grid during off-grid to grid-connected control by proposing a new control strategy, thereby improving the quality and stability of power transmission.

[0051] (2) The present invention proposes that the PCS collects the voltage and current at both ends of the contactor to characterize the voltage and current on the grid side and the microgrid side. By controlling the grid-connected point circuit breaker and the microgrid-side contactor to close separately, the microgrid system can have better adaptability and no longer require the PCS to complete status monitoring and closing work in milliseconds. This greatly reduces the difficulty of off-grid to grid-connected operation and can also reduce the equipment cost of the entire power system. It has better usability and stability in system debugging and power product transmission.

[0052] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0053] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0054] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0055] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0056] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0057] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A control method for off-grid to grid-connected microgrid based on photovoltaic storage and charging, based on a circuit breaker and a contactor connected in series between the grid side and the microgrid side, characterized in that the method include: According to the off-grid to grid-connected instruction, confirm whether the circuit breaker's opening state is normal, and control the grid-connected point circuit breaker to close when the opening state is confirmed to be normal; The voltage and current of the grid side and the microgrid side are collected to determine whether the microgrid side and the grid side meet the synchronization conditions. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

2. According to the method for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging according to claim 1, it is characterized in that: The step of confirming whether the opening state of the circuit breaker is normal according to the off-grid to grid-connected instruction includes: Detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side; If the zero drift value of the grid-connected point circuit breaker is within a preset range, it is determined that the grid-connected point circuit breaker opening state is normal; otherwise, it is determined that the grid-connected point circuit breaker opening state is abnormal.

3. A method for controlling off-grid and grid-connected microgrid based on photovoltaic storage and charging according to claim 1 or 2, characterized in that: The collecting of the voltage and current of the grid side and the microgrid side to determine whether the microgrid side and the grid side meet the synchronization condition includes: Collect the voltage and current on the grid side and microgrid side respectively; According to the collected voltages and currents on the grid side and the microgrid side, the amplitude, phase, and frequency of the grid side voltage and the amplitude, phase, and frequency of the microgrid side voltage are extracted respectively; Calculate the amplitude difference, phase difference and frequency difference between the grid-side voltage and the microgrid-side voltage; Based on the calculated amplitude difference, phase difference and frequency difference, it is determined whether the grid side and the microgrid side meet the synchronization conditions.

4. According to the method of controlling off-grid to grid-connected microgrid based on photovoltaic storage and charging according to claim 3, it is characterized in that: The voltage and current of the grid side and the microgrid side are collected respectively, including: By collecting the voltage and current at both ends of the contactor, the voltage and current on the grid side and the microgrid side are obtained.

5. According to the method of controlling off-grid to grid-connected microgrid based on photovoltaic storage and charging according to claim 3, it is characterized in that: The step of judging whether the grid side and the microgrid side meet the synchronization conditions based on the calculated amplitude difference, phase difference, and frequency difference includes: If the phase sequence of the grid side and the microgrid side is the same according to the calculated phase difference between the grid side and the microgrid side, and the phase difference, amplitude difference and frequency difference between the grid side and the microgrid side are within the preset range, then it is determined that the grid side and the microgrid side meet the synchronization conditions; Otherwise, it is determined that the grid side and the microgrid side do not meet the synchronization conditions.

6. A microgrid off-grid to grid-connected control system based on photovoltaic storage and charging, characterized in that: Includes EMS controller and PCS, including: The EMS controller is used to confirm whether the opening state of the circuit breaker is normal according to the monitoring data of the PCS when the off-grid to grid-connected instruction is detected in real time. When the opening state is confirmed to be normal, the circuit breaker at the grid-connected point is controlled to close and the off-grid to grid-connected instruction is sent to the PCS; PCS is used to monitor the voltage and current at both ends of the microgrid contactor in real time, and judge whether the microgrid side and the grid side meet the synchronization conditions based on the collected voltage and current. If the synchronization conditions are met, the microgrid side contactor is controlled to close.

7. A microgrid off-grid to grid-connected control system based on photovoltaic storage and charging according to claim 6, characterized in that: The EMS controller sends an off-grid to on-grid switching instruction to the PCS via the modbus TCP communication mode.

8. According to the control system of a microgrid off-grid to grid-connected based on photovoltaic storage and charging according to claim 6, it is characterized in that: The PCS includes a zero drift detection module, and the EMS controller includes a state judgment module, wherein: The zero drift detection module is used to detect the zero drift value of the grid-connected point circuit breaker in the open state, which is away from the grid side; The state judgment module is used to judge whether the zero drift value of the grid-connected point circuit breaker is within a preset range. If the zero drift value of the grid-connected point circuit breaker is within the preset range, it is judged that the grid-connected point circuit breaker opening state is normal; otherwise, it is judged that the grid-connected point circuit breaker opening state is abnormal.

9. A microgrid off-grid to grid-connected control system based on photovoltaic storage and charging according to claim 7 or 8, characterized in that: The PCS also includes a voltage / current detection module, a parameter operation module and a synchronization condition judgment module, wherein: The voltage / current detection module is used to collect the voltage and current of the grid side and the microgrid side respectively; The parameter operation module is used to extract the amplitude, phase, and frequency of the grid-side voltage and the amplitude, phase, and frequency of the microgrid-side voltage respectively according to the collected voltage and current on the grid-side and microgrid-side; and is also used to calculate the amplitude difference, phase difference, and frequency difference between the grid-side voltage and the microgrid-side voltage; The synchronization condition judgment module is used to judge whether the grid side and the microgrid side meet the synchronization conditions based on the calculated amplitude difference, phase difference, and frequency difference.

10. A microgrid off-grid to grid-connected control system based on photovoltaic storage and charging according to claim 9, characterized in that: The synchronization condition judgment module includes a phase sequence judgment submodule, a phase difference judgment submodule, an amplitude judgment submodule, a frequency judgment submodule and a synchronization comprehensive judgment submodule, wherein: The phase sequence judgment submodule is used to judge whether the phase sequence of the grid side and the microgrid side is the same according to the phase difference between the grid side and the microgrid side; The phase difference judgment submodule is used to judge whether the phase difference between the grid side and the microgrid side is within a preset phase difference range; The amplitude judgment submodule is used to judge whether the amplitude difference between the grid side and the microgrid side is within a preset amplitude difference range; The frequency determination submodule is used to determine whether the frequency difference between the grid side and the microgrid side is within a preset frequency difference range; The synchronization comprehensive judgment submodule is used to determine that the grid side and the microgrid side meet the synchronization conditions when the phase sequence of the grid side and the microgrid side is the same, the phase difference is within a preset phase difference range, the amplitude difference is within a preset amplitude difference range, and the frequency difference is within a preset frequency difference range.

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