Off-grid and grid-connected switching method, off-grid and grid-connected switching device and system of parallel operation system

Abstract

The embodiment of the invention discloses an off-grid and grid-connected switching method, an off-grid and grid-connected switching device and an off-grid and grid-connected switching system of a parallel operation system, which are used for the technical field of parallel operation control. Wherein in the off-grid and grid-connected switching process of the parallel operation system, when a parallel operation control panel detects that the voltage difference between the two ends of a power grid contactor meets a contactor pull-in condition, the power grid contactor is controlled to be pulled in; when it is determined that the power grid contactor is reliably closed, the parallel operation control panel sends a grid-connected starting instruction to the multiple inverters, and the multiple inverters are controlled to enter grid-connected driving after off-grid driving is closed; that is to say, reliable actuation of the power grid contactor is ensured before the inverter stops driving, power is supplied to the load through the power grid after actuation of the power grid contactor, and no power failure of the load can be ensured. The method comprises the following steps of: controlling a plurality of inverters to close grid-connected driving in a grid-connected and off-grid switching process of a parallel system; and the parallel operation control panel sends an off-grid starting instruction to the plurality of inverters to control the plurality of inverters to enter off-grid driving, so that the load can be quickly electrified again.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of parallel control, and in particular to an off-grid switching method, an off-grid switching device and a system for a parallel system. Background Art

[0002] The power grid supplies power to loads in many places. During operation, the power grid may experience power grid anomalies due to transformer damage or line maintenance, making it difficult to continue to supply power to the loads. In various occasions, continuous and uninterrupted power supply is usually required, and backup power sources (such as batteries, photovoltaic panels, etc.) are usually used. When a power grid anomaly is detected, the backup power source is used to start the power supply.

[0003] The existing parallel system includes: multiple backup power supplies and inverters corresponding to each backup power supply. After multiple inverters are connected in parallel, they are connected to the load, and the power grid is connected to the load. When the power grid is abnormal, the parallel system switches from grid-connected to off-grid, disconnects the power supply of the grid, and the backup power supplies supply power to the load through the inverter voltage output by the inverter; when the power grid returns to normal, the parallel system switches from off-grid to grid-connected, and the power supply of the grid is restored.

[0004] However, in the process of switching from grid to off-grid or switching from off-grid to grid in a parallel system, it is easy for the load to lose power; therefore, there is an urgent need for a grid-connected and off-grid switching method for a parallel system to minimize the power-off duration of the load. Summary of the invention

[0005] The embodiments of the present application provide an off-grid switching method, an off-grid switching device and a system for a parallel system, which can ensure that the load does not lose power when switching off the grid and switching on the grid, and reduce the power-off duration of the load when switching on the grid and off the grid.

[0006] The embodiment of the present application provides an off-grid switching method for a parallel system, the parallel system comprising: a parallel device and multiple inverters, the parallel device comprising: a parallel control board and a grid contactor; the parallel control board communicates with the multiple inverters in parallel, the input ends of the multiple inverters are connected to corresponding backup power supplies, the output ends of the multiple inverters are connected to the load and one end of the grid contactor respectively after being connected in parallel, and the other end of the grid contactor is connected to the grid, the off-grid switching method comprises:

[0007] When the parallel system is in an off-grid operation state, when the parallel control board detects that the grid is normal, the parallel control board controls the inverter phase of the multiple inverters to be locked to the grid phase; when the parallel control board detects that the voltage difference across the grid contactor meets the contactor energizing condition, the grid contactor is controlled to be energized; when it is determined that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup instruction to the multiple inverters, controls the multiple inverters to enter the grid-connected drive after turning off the off-grid drive, so that the parallel system enters the grid-connected operation state;

[0008] When the parallel system is in a grid-connected operation state, when the parallel control board detects a grid abnormality, the parallel control board controls the grid contactor to disconnect, and controls the multiple inverters to shut down the grid-connected drive; the parallel control board sends an off-grid startup instruction to the multiple inverters, controls the multiple inverters to enter the off-grid drive, so that the parallel system enters the off-grid operation state.

[0009] Furthermore, the parallel control board controls the inverter phases of the multiple inverters to be locked to the grid phase, including:

[0010] The parallel control board sends the grid phase and grid amplitude information to the multiple inverters, controls the multiple inverters to switch the inverter phase from the self-oscillation phase to the grid phase, and controls the multiple inverters to switch the inverter effective value from the rated voltage to the grid amplitude.

[0011] Furthermore, the parallel control board detects that the voltage difference across the grid contactor satisfies the contactor pickup condition, including:

[0012] If the parallel control board detects that the voltage difference between the two ends of the grid contactor is less than a preset voltage threshold, it is determined that the contactor pickup condition is met;

[0013] The parallel control board detects that the voltage difference between the two ends of the grid contactor is greater than or equal to the preset voltage threshold, and then determines that the contactor pickup condition is not met.

[0014] Further, determining that the grid contactor is reliably engaged includes:

[0015] After the parallel control board sends a pull-in instruction to the grid contactor, it is determined that the grid contactor is reliably pulled in after a preset pull-in time delay.

[0016] Furthermore, the parallel control board sends a grid-connected startup instruction to the multiple inverters, and controls the multiple inverters to enter grid-connected drive after being driven off, including:

[0017] The parallel control board sends a grid-connected startup instruction to the multiple inverters, controls the multiple inverters to turn off driving after receiving the grid-connected startup instruction, and controls the multiple inverters to turn on grid-connected driving after delaying for a preset shutdown time.

[0018] Further, the controlling the plurality of inverters to shut down driving includes:

[0019] The parallel control board sends an off-grid mode instruction to the multiple inverters to control the multiple inverters to start shutting down the drive;

[0020] After receiving the drive shutdown information fed back by the multiple inverters, the parallel control board determines that the multiple inverters have all completed the shutdown drive.

[0021] Furthermore, the method further comprises:

[0022] The parallel control board sends off-grid mode instructions to the multiple inverters, controls the multiple inverters to switch the inverter phase from the grid phase to the self-oscillation phase, and controls the multiple inverters to switch the inverter effective value from the grid amplitude to the rated voltage.

[0023] Furthermore, the method further comprises:

[0024] The parallel control board samples the grid voltage to obtain voltage sampling data;

[0025] The parallel control board sums the absolute values ​​of the voltage sampling data to obtain a target voltage value, and compares the target voltage value with a preset reference threshold value. If the target voltage value is greater than or equal to the preset reference threshold value, it is determined that the power grid is normal; if the target voltage value is less than the preset reference threshold value, it is determined that the power grid is abnormal.

[0026] The embodiment of the present application provides an off-grid switching device of a parallel system, the parallel system comprising: a parallel device, a plurality of inverters, the parallel device comprising: a parallel control board and a grid contactor; the parallel control board communicates with the plurality of inverters in parallel, the input ends of the plurality of inverters are connected to corresponding backup power supplies, the output ends of the plurality of inverters are connected to a load and one end of the grid contactor respectively after being connected in parallel, the other end of the grid contactor is connected to the grid, the off-grid switching device comprises:

[0027] A first control unit is used for, when the parallel system is in an off-grid operation state, controlling the parallel control board to lock the inverter phase of the multiple inverters to the grid phase when it is detected that the grid is normal; when it is detected that the voltage difference across the grid contactor meets the contactor energizing condition, controlling the parallel control board to energize the grid contactor; when it is determined that the grid contactor is reliably energized, controlling the parallel control board to send a grid-connected startup instruction to the multiple inverters, so as to control the multiple inverters to enter the grid-connected drive after turning off the off-grid drive, so that the parallel system enters the grid-connected operation state;

[0028] The second control unit is used to control the parallel control board to disconnect the grid contactor and shut down the grid-connected drive of the multiple inverters when a grid abnormality is detected when the parallel system is in a grid-connected operation state; and control the parallel control board to send an off-grid startup instruction to the multiple inverters to control the multiple inverters to enter off-grid drive, so that the parallel system enters an off-grid operation state.

[0029] An embodiment of the present application provides a computer-readable storage medium, which includes instructions. When the instructions are executed on a computer, the computer executes the above method.

[0030] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0031] In an embodiment of the present application, during the off-grid and grid-connected process of the parallel system, when the parallel control board detects that the voltage difference across the grid contactor meets the contactor energizing condition, the grid contactor is controlled to be energized; after determining that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup command to multiple inverters, and controls the multiple inverters to enter the grid-connected drive after turning off the off-grid drive; that is, before the inverter turns off the drive, it is ensured that the grid contactor is reliably energized, and after the grid contactor is energized, the load is powered by the grid, which can ensure that the load does not lose power; during the grid-connected and grid-connected process of the parallel system, after controlling multiple inverters to turn off the grid-connected drive; the parallel control board sends an off-grid startup command to multiple inverters, and controls the multiple inverters to enter the off-grid drive, which can quickly power on the load and reduce the power-off time of the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0033] Figure 1 A schematic diagram of a parallel system disclosed in an embodiment of the present application;

[0034] Figure 2 A flow chart of off-grid switching of a parallel system disclosed in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of off-grid switching of a parallel system disclosed in an embodiment of the present application;

[0036] Figure 4 A diagram of an off-grid switching device for a parallel system disclosed in an embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] In the description of the embodiments of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on the embodiments of the present application.

[0039] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0040] The existing parallel system includes: multiple backup power supplies and an inverter corresponding to each backup power supply. After the multiple inverters are connected in parallel, they are connected to the load, and the power grid is connected to the load. When the power grid is abnormal, the parallel system switches from grid-connected to off-grid, disconnects the power supply of the power grid, and the backup power supplies supply power to the load through the inverter voltage output by the inverter; when the power grid returns to normal, the parallel system switches from off-grid to grid-connected, and the power supply of the power grid is restored. However, in the process of switching from grid-connected to off-grid or from off-grid to grid-connected in the parallel system, it is easy for the load to lose power; therefore, an embodiment of the present application provides an off-grid and grid-connected switching method for a parallel system, which can ensure that the load does not lose power when switching from off-grid to grid-connected, and reduce the power-off duration of the load when switching from grid-connected to off-grid.

[0041] In the embodiment of the present application, the parallel system is as follows Figure 1 As shown, the parallel system includes: a parallel device, multiple inverters, and the parallel device includes: a parallel control board and a grid contactor; the parallel control board communicates with multiple inverters in parallel, and can communicate in parallel through a parallel communication line (such as a CAN bus); the input ends of the multiple inverters are connected to the corresponding backup power supply, and the output ends of the multiple inverters are connected to the load and one end of the grid contactor respectively after being connected in parallel, and the other end of the grid contactor is connected to the grid; wherein, the backup power supply can be a power generation device or energy storage system such as a battery BAT or a photovoltaic panel PV, and the specific details are not limited here. The output ends of the multiple inverters can be connected in parallel through the parallel interface on the parallel device, and are connected to the load and the grid after being connected in parallel; the inverter outputs of the multiple inverters can be transmitted to the load, and the grid supplies power to the load through the grid contactor. Among them, when the parallel system is in the grid-connected operation state, if the output power of the inverter is greater than the power demand of the load, the power of the load is all supplied by the inverter, and no power from the grid flows to the load, and the excess power output by the inverter will flow to the grid and feed the grid; if the output power of the inverter cannot meet the power demand of the load, at this time, the grid and the inverter provide power to the load together, that is, the grid and the inverter are supplying power to the load at the same time.

[0042] In the embodiment of the present application, the parallel control board can determine the off-grid mode according to the grid status, and can send the off-grid mode command and the on / off command to each inverter through the CAN bus. After the inverter receives the off-grid mode command and the on / off command sent by the parallel control board, it switches between off-grid drive and grid drive. By controlling the grid contactor and the off-grid drive of the inverter, the off-grid switching is realized. The off-grid switching process of the parallel system is as follows: Figure 2 As shown, the following steps are included:

[0043] In the embodiment of the present application, the process of the parallel system switching from off-grid to on-grid includes steps 201 to 203, which are as follows:

[0044] 201. When the parallel system is in off-grid operation, when the parallel control board detects that the grid is normal, the parallel control board controls the inverter phases of multiple inverters to be locked to the grid phase.

[0045] In the embodiment of the present application, when the parallel system is in an off-grid operation state, when the parallel control board detects that the power grid is normal, the parallel control board controls the inverter phase of the multiple inverters to be locked to the power grid phase. It can be understood that when the parallel system is in an off-grid operation state, the power grid voltage is in an abnormal state, the power grid contactor is in a disconnected state, the power grid does not supply power to the load, and the inverter is in an off-grid drive, that is, the inverter is equivalent to a voltage source, and the load is powered by the inverter voltage output by the inverter.

[0046] When the parallel control board detects that the grid voltage returns to normal (grid is normal), the grid phase can be locked and sent to multiple inverters through the CAN bus. Multiple inverters are paralleled and off-grid phase-locked to the grid phase. At this time, the phase of the inverter voltage of multiple inverters tracks the grid voltage.

[0047] 202. When the parallel control board detects that the voltage difference across the grid contactor meets the contactor closure condition, it controls the grid contactor to closure.

[0048] After the inverter phase of multiple inverters is locked to the grid phase, when the parallel control board detects that the voltage difference across the grid contactor meets the contactor energizing condition, the grid contactor is controlled to energize. It can be understood that the voltage difference across the grid contactor is the voltage difference between the inverter voltage output by the inverter and the grid voltage.

[0049] Specifically, if the parallel control board detects that the voltage difference across the grid contactor is less than the preset voltage threshold, it is determined that the contactor closure condition is met; if the parallel control board detects that the voltage difference across the grid contactor is greater than or equal to the preset voltage threshold, it is determined that the contactor closure condition is not met. The preset voltage threshold can be 30V or 20V, which is not specifically limited here. The parallel control board can send a closing signal (such as a high-level signal or a low-level signal) to the grid contactor to control the grid contactor to close.

[0050] 203. When it is determined that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup command to multiple inverters, controlling the multiple inverters to enter grid-connected drive after shutting down off-grid drive.

[0051] When it is determined that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup command to multiple inverters, controlling multiple inverters to enter grid-connected drive after shutting down off-grid drive, so that the parallel system enters the grid-connected operation state.

[0052] Among them, after the parallel control board sends the pull-in instruction to the grid contactor, it can delay the preset pull-in time to determine that the grid contactor is reliably pulled in. Among them, the preset pull-in time can be determined based on the pull-in action time of the grid contactor, which can be 100ms or 120ms, which is not limited here. The parallel control board can send grid-connected startup instructions to multiple inverters through the CAN bus, control multiple inverters to shut down the drive for a period of time, and then enter the grid-connected drive. It is understandable that when the inverter is converted from off-grid drive to grid-connected drive, the inverter needs to turn off the drive to reset the parameters in the inverter to avoid interference. When the inverter is in grid-connected drive, the inverter is equivalent to a current source, controlling the energy storage power of the backup power supply and the power output to the load. At this time, the load can be powered by the grid or by the inverter.

[0053] It can be understood that after ensuring that the grid contactor is reliably energized, multiple inverters are controlled to shut down the off-grid drive, that is, after the grid supplies power to the load, the inverter can be turned off and the inverter can be converted to a grid-connected drive, effectively avoiding power loss of the load when the inverter turns off the drive; that is, the load does not lose power during the entire process of switching the parallel system from off-grid to grid-connected, and the load power-off duration is 0s, meeting the power-off time indicator requirement.

[0054] In the embodiment of the present application, the process of the parallel system in connecting to the grid and disconnecting from the grid includes steps 204 to 205, which are specifically as follows:

[0055] 204. When the parallel system is in the grid-connected operation state, when the parallel control board detects a grid abnormality, the parallel control board controls the grid contactor to disconnect and controls multiple inverters to shut down the grid-connected drive.

[0056] In the embodiment of the present application, when the parallel system is in the grid-connected operation state, when the parallel control board detects an abnormality in the grid, the parallel control board controls the grid contactor to disconnect and controls multiple inverters to shut down the drive. It can be understood that when the parallel system is in the grid-connected operation state, the grid voltage is in a normal state, the grid contactor is in a closed state, the grid supplies power to the load, and the inverter is in grid-connected drive.

[0057] When the power grid fails, the parallel control board detects the abnormality of the power grid. In order to avoid the overvoltage or undervoltage caused by the abnormal power grid affecting the load, the parallel control board needs to control the grid contactor to disconnect and switch the parallel system mode from the grid-connected mode to the off-grid mode. The parallel control board can send off-grid mode instructions to multiple inverters to control multiple inverters to start shutting down the grid-connected drive; after receiving the off-grid mode instruction, the inverter shuts down the grid-connected drive and sends its own drive status information to the parallel control board, which includes the drive shutdown information; after receiving the drive shutdown information fed back by multiple inverters, the parallel control board determines that multiple inverters have completed the shutdown drive.

[0058] 205. The parallel control board sends off-grid startup instructions to multiple inverters to control the multiple inverters to enter off-grid drive.

[0059] After determining that multiple inverters have completed shutdown driving, the parallel control board can send off-grid startup instructions to multiple inverters to control multiple inverters to enter off-grid driving, that is, after receiving the off-grid startup instruction, multiple inverters will re-start the parallel off-grid to make the parallel system enter the off-grid operation state.

[0060] It can be seen that in the embodiment of the present application, during the off-grid and grid-connected process of the parallel system, when the parallel control board detects that the voltage difference across the grid contactor meets the contactor closure condition, it controls the grid contactor to closure; when it is determined that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup command to multiple inverters, and controls the multiple inverters to enter the grid-connected drive after turning off the off-grid drive; that is, before the inverter turns off the drive, it is ensured that the grid contactor is reliably energized, and after the grid contactor is energized, the load is powered by the grid, which can ensure that the load is not powered off; during the grid-connected and grid-connected process of the parallel system, after controlling multiple inverters to turn off the grid-connected drive; the parallel control board sends an off-grid startup command to multiple inverters, and controls multiple inverters to enter the off-grid drive, which can quickly power on the load and reduce the power-off time of the load.

[0061] The following will be combined Figure 3 , the off-grid switching process of the parallel system is further described. In the figure, in the inverter switch of CAN: 2 represents the off-grid startup command, 1 represents the grid startup command, in the inverter switch of CAN: 1 represents the grid mode command, 0 represents the off-grid mode command; ESS represents the inverter, INV drive represents the inverter drive, INV phase represents the inverter phase, and INV effective value represents the inverter effective value. The corresponding off-grid switching timing is shown in Table 1 below:

[0062] Table 1

[0063]

[0064]

[0065] The process of switching from off-grid to grid-connected in the parallel system is as follows: t0: grid recovery, t0-t1 (i.e. T0): the duration of the parallel control board detecting that the grid is normal; t1: the parallel control board sends grid phase information to multiple inverters. It can be understood that the parallel control board can send grid phase and grid amplitude information to multiple inverters, control multiple inverters to switch the inverter phase from the self-oscillation phase to the grid phase, and control multiple inverters to switch the inverter effective value from the rated voltage to the grid amplitude; t1 -t2 (i.e. T1): the duration of the voltage difference between the two ends of the grid contactor detected by the parallel control board; at t2: the parallel control board controls the grid contactor to close; t2-t3: delay for a certain period of time to ensure that the grid contactor is reliably closed; at t3: the parallel control board sends a grid-connected startup command to multiple inverters, controls multiple inverters to turn off the off-grid drive after receiving the grid-connected startup command, and controls multiple inverters to turn on the grid-connected drive after delaying the preset shutdown time (T3); the load does not lose power during the off-grid switching and grid-connected process.

[0066] The process of grid connection and disconnection in the parallel system is as follows: t4: grid abnormality; t4-t5 (i.e. T4): the duration of the parallel control board detecting grid abnormality; t5: the parallel control board controls the grid contactor to disconnect; t5-t6 (i.e. T5): the parallel control board sends an off-grid mode command; t6: the inverter turns off the grid-connected drive, multiple inverters receive the off-grid mode command, multiple inverters switch the inverter phase from the grid phase to the self-oscillation phase, and multiple inverters switch the inverter effective value from the grid amplitude to the rated voltage. t6-t7 (i.e. T6): the duration of the parallel control board detecting that multiple inverters have blocked the drive; t7: the parallel control board sends an off-grid start command, and the inverter enters the off-grid drive. It can be understood that the grid-connected contactor of the inverter and the output relay of the inverter in the parallel system remain in the energized state; the parallel control board sends phase information, off-grid startup instructions and off-grid mode instructions through the CAN bus through status frames. There may be synchronization frames and current sharing frames in the CAN bus. The priority of synchronization frames and current sharing frames is higher than that of status frames. At this time, there is a communication delay.

[0067] It can be seen that considering the communication delay and contactor action time, the switching time from off-grid to grid-connected is 0ms, and the index requirement is 150ms; the switching time from grid-connected to off-grid (t4-t7) is about 106ms, and the index requirement is 150ms; the switching time from off-grid to grid-connected and from grid-connected to off-grid can meet the index requirements.

[0068] Furthermore, in an embodiment of the present application, the parallel control board can also sample the grid voltage to obtain voltage sampling data; the parallel control board sums the absolute values ​​of the voltage sampling data to obtain a target voltage value, and compares the target voltage value with a preset reference threshold value. If the target voltage value is greater than or equal to the preset reference threshold value, it is determined that the grid is normal; if the target voltage value is less than the preset reference threshold value, it is determined that the grid is abnormal. The preset threshold value can be half of the rated voltage of the grid. The parallel control board can determine in real time whether the grid is in a normal or abnormal state by sampling the grid voltage in real time.

[0069] The embodiment of the present application also provides an off-grid switching device for a parallel system, the parallel system comprising: a parallel device, a plurality of inverters, the parallel device comprising: a parallel control board and a grid contactor; the parallel control board communicates with the plurality of inverters in parallel, the input ends of the plurality of inverters are connected to corresponding backup power supplies, the output ends of the plurality of inverters are connected to a load and one end of the grid contactor respectively after being connected in parallel, and the other end of the grid contactor is connected to the grid, such as Figure 4 As shown, the off-grid and on-grid switching device comprises:

[0070] The first control unit 401 is used for controlling the parallel control board to lock the inverter phase of the multiple inverters to the grid phase when the grid is detected to be normal when the parallel system is in an off-grid operation state; controlling the parallel control board to close the grid contactor when it is detected that the voltage difference across the grid contactor meets the contactor energizing condition; and controlling the parallel control board to send a grid-connected startup instruction to the multiple inverters after determining that the grid contactor is reliably energized, so as to control the multiple inverters to enter the grid-connected drive after turning off the off-grid drive, so that the parallel system enters the grid-connected operation state;

[0071] The second control unit 402 is used to control the parallel control board to disconnect the grid contactor and shut down the grid-connected drive of the multiple inverters when a grid abnormality is detected when the parallel system is in a grid-connected operation state; control the parallel control board to send an off-grid startup instruction to the multiple inverters to control the multiple inverters to enter off-grid drive, so that the parallel system enters an off-grid operation state.

[0072] An embodiment of the present application provides a computer-readable storage medium, which includes instructions. When the instructions are executed on a computer, the computer executes the method described above.

[0073] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0074] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0075] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0076] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0077] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, read-only memory), random access memory (RAM, random access memory), disk or optical disk and other media that can store program code.

Claims

1. A method for switching off and on-grid of a parallel system, characterized in that: The parallel system comprises: a parallel device and multiple inverters, wherein the parallel device comprises: a parallel control board and a grid contactor; the parallel control board communicates with the multiple inverters in parallel, the input ends of the multiple inverters are connected to corresponding backup power supplies, the output ends of the multiple inverters are connected to the load and one end of the grid contactor respectively after being connected in parallel, and the other end of the grid contactor is connected to the grid, and the off-grid switching method comprises: When the parallel system is in an off-grid operation state, when the parallel control board detects that the grid is normal, the parallel control board controls the inverter phase of the multiple inverters to be locked to the grid phase; when the parallel control board detects that the voltage difference across the grid contactor meets the contactor energizing condition, the grid contactor is controlled to be energized; when it is determined that the grid contactor is reliably energized, the parallel control board sends a grid-connected startup instruction to the multiple inverters, controls the multiple inverters to enter the grid-connected drive after turning off the off-grid drive, so that the parallel system enters the grid-connected operation state; When the parallel system is in a grid-connected operation state, when the parallel control board detects a grid abnormality, the parallel control board controls the grid contactor to disconnect, and controls the multiple inverters to shut down the grid-connected drive; the parallel control board sends an off-grid startup instruction to the multiple inverters, controls the multiple inverters to enter the off-grid drive, so that the parallel system enters the off-grid operation state.

2. The off-grid switching method according to claim 1, characterized in that: The parallel control board controls the inverter phases of the multiple inverters to be locked to the grid phase, including: The parallel control board sends the grid phase and grid amplitude information to the multiple inverters, controls the multiple inverters to switch the inverter phase from the self-oscillation phase to the grid phase, and controls the multiple inverters to switch the inverter effective value from the rated voltage to the grid amplitude.

3. The off-grid switching method according to claim 1, characterized in that: The parallel control board detects that the voltage difference across the grid contactor meets the contactor pickup condition, which includes: If the parallel control board detects that the voltage difference between the two ends of the grid contactor is less than a preset voltage threshold, it is determined that the contactor pickup condition is met; The parallel control board detects that the voltage difference between the two ends of the grid contactor is greater than or equal to the preset voltage threshold, and then determines that the contactor pickup condition is not met.

4. The off-grid switching method according to claim 1, characterized in that: Determining that the grid contactor is reliably attracted includes: After the parallel control board sends a pull-in instruction to the grid contactor, it is determined that the grid contactor is reliably pulled in after a preset pull-in time delay.

5. The off-grid switching method according to claim 1, characterized in that: The parallel control board sends a grid-connected startup instruction to the multiple inverters, and controls the multiple inverters to enter grid-connected driving after being shut down, including: The parallel control board sends a grid-connected startup instruction to the multiple inverters, controls the multiple inverters to turn off driving after receiving the grid-connected startup instruction, and controls the multiple inverters to turn on grid-connected driving after delaying for a preset shutdown time.

6. The off-grid switching method according to claim 1, characterized in that: The controlling the plurality of inverters to shut down driving comprises: The parallel control board sends an off-grid mode instruction to the multiple inverters to control the multiple inverters to start shutting down the driving; After receiving the drive shutdown information fed back by the multiple inverters, the parallel control board determines that the multiple inverters have all completed the shutdown drive.

7. The off-grid switching method according to claim 1, characterized in that: The method further comprises: The parallel control board sends off-grid mode instructions to the multiple inverters, controls the multiple inverters to switch the inverter phase from the grid phase to the self-oscillation phase, and controls the multiple inverters to switch the inverter effective value from the grid amplitude to the rated voltage.

8. The off-grid switching method according to claim 1, characterized in that: The method further comprises: The parallel control board samples the grid voltage to obtain voltage sampling data; The parallel control board sums the absolute values ​​of the voltage sampling data to obtain a target voltage value, and compares the target voltage value with a preset reference threshold value. If the target voltage value is greater than or equal to the preset reference threshold value, it is determined that the power grid is normal; if the target voltage value is less than the preset reference threshold value, it is determined that the power grid is abnormal.

9. A grid-connected switching device for a parallel system, characterized in that: The parallel system comprises: a parallel device and multiple inverters, wherein the parallel device comprises: a parallel control board and a grid contactor; the parallel control board communicates with the multiple inverters in parallel, the input ends of the multiple inverters are connected to corresponding backup power supplies, the output ends of the multiple inverters are connected to the load and one end of the grid contactor respectively after being connected in parallel, and the other end of the grid contactor is connected to the grid, and the off-grid switching device comprises: A first control unit is used for, when the parallel system is in an off-grid operation state, controlling the parallel control board to lock the inverter phase of the multiple inverters to the grid phase when it is detected that the grid is normal; when it is detected that the voltage difference across the grid contactor meets the contactor energizing condition, controlling the parallel control board to energize the grid contactor; when it is determined that the grid contactor is reliably energized, controlling the parallel control board to send a grid-connected startup instruction to the multiple inverters, so as to control the multiple inverters to enter the grid-connected drive after turning off the off-grid drive, so that the parallel system enters the grid-connected operation state; The second control unit is used to control the parallel control board to disconnect the grid contactor and shut down the grid-connected drive of the multiple inverters when a grid abnormality is detected when the parallel system is in a grid-connected operation state; and control the parallel control board to send an off-grid startup instruction to the multiple inverters to control the multiple inverters to enter off-grid drive, so that the parallel system enters an off-grid operation state.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium comprises instructions, and when the instructions are executed on a computer, the computer is caused to perform the method according to any one of claims 1 to 8.

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