Off-grid and grid-connected switching control method, switching device, inverter device, and power supply system

Abstract

An off-grid and grid-connected switching control method, comprising: when a grid supplies power, a switching device sends a first signal to an inverter device by means of a power connection line, so that the inverter device operates in a grid-connected mode on the basis of the first signal; and when the grid fails, the switching device disconnects, so that the path between an output interface of the inverter device and the grid is cut off, and the switching device sends a second signal to the inverter device by means of the power connection line, so that the inverter device switches, on the basis of the second signal, the operating mode from the grid-connected mode to an off-grid mode for operation, and operates on the basis of a signal frequency and signal phase corresponding to the second signal. Thus, rapid grid-connected and off-grid switching of the inverter device is achieved.

Description

Off-grid to on-grid switching control methods, switching devices, inverters and power supply systems

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411219505.7, filed on August 30, 2024, entitled "On-grid / Off-grid Switching Control Method, Switching Device, Inverter Device and Power Supply System", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of inverter technology, specifically to an off-grid / on-grid switching control method, a switching device, an inverter, and a power supply system. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute exemplary technology.

[0005] Microgrids based on energy storage systems can operate off-grid during grid failures, continuously supplying power to loads. When the grid returns to normal, the microgrid system needs to exit off-grid mode and switch to grid-connected mode. The inverters in the energy storage system can be used for both off-grid and grid-connected operation.

[0006] During off-grid operation with load, if the power grid returns to normal, the off-grid to grid-connected control strategy can be activated. Conversely, during grid-connected operation, if the power grid fails, the grid-connected to off-grid control strategy can be activated.

[0007] A controllable switching device is required between the inverter and the power grid to ensure system safety. When the inverter and the switching device are independent components, they need to exchange information to perform on-grid / off-grid switching. In related solutions, multiple communication lines are typically used between the inverter and the switching device for information exchange, making the process complex. Therefore, simplifying the information exchange between the inverter and the switching device, and achieving rapid on-grid / off-grid switching for the inverter, are pressing issues that need to be addressed in this field. Summary of the Invention

[0008] According to various embodiments of this application, an off-grid / on-grid switching control method, a switching device, an inverter, and a power supply system are provided.

[0009] The first aspect of this application provides an off-grid / on-grid switching control method applied to a switching device in a power supply system. The power supply system includes an inverter, a switching device, and a power connection line. The output interface of the inverter is used to connect to a first interface of the switching device and a load. The second interface of the switching device is used to connect to the power grid. The switching device and the inverter are communicatively connected via the power connection line. The off-grid / on-grid switching control method includes: when the power grid supplies power, sending a first signal to the inverter via the power connection line, the first signal being used to indicate that the inverter operates in grid-connected mode; when the power grid fails, controlling the switching device to disconnect and sending a second signal to the inverter via the power connection line, the second signal having a different waveform from the first signal, the second signal being used to indicate that the inverter switches its operating mode from grid-connected mode to off-grid mode, and operates according to the signal frequency and signal phase corresponding to the second signal.

[0010] A second aspect of this application provides a switching device disposed in a power supply system. The power supply system further includes an inverter and a power connection line. The output interface of the inverter is used to connect a first interface of the switching device and a load. The second interface of the switching device is used to connect to the power grid. The switching device is communicatively connected to the inverter via the power connection line. The switching device includes: a switching circuit for disconnecting or connecting the connection between the first and second interfaces; and a control circuit connected to the switching circuit and the power connection line. The control circuit is used to: when the power grid supplies power, send a first signal to the inverter via the power connection line, the first signal indicating that the inverter operates in grid-connected mode; when the power grid fails, control the switching circuit to disconnect and send a second signal to the inverter via the power connection line, the second signal having a different waveform from the first signal, the second signal indicating that the inverter switches its operating mode from grid-connected mode to off-grid mode, and operates according to the signal frequency and signal phase corresponding to the second signal.

[0011] A third aspect of this application provides an inverter device installed in a power supply system. The power supply system further includes a switching device and a power connection line. The output interface of the inverter device is used to connect to a first interface of the switching device and a load. The second interface of the switching device is used to connect to the power grid. The inverter device is communicatively connected to the switching device via the power connection line. The inverter device includes: a power conversion circuit that outputs and / or receives power through the output interface; and a main control circuit connected to the power connection line and the power conversion circuit. The main control circuit is used to: monitor the signal transmitted on the power connection line; when a first signal is detected transmitted on the power connection line, control the power conversion circuit to operate in grid-connected mode; when the signal transmitted on the power connection line changes from the first signal to a second signal, switch the operating mode of the power conversion circuit from grid-connected mode to off-grid mode, and operate according to the signal frequency and signal phase corresponding to the second signal; wherein the second signal has a different waveform from the first signal.

[0012] The fourth aspect of this application provides a power supply system, including the inverter device described in the third aspect, a power connection line, and the switching device described in the second aspect or any embodiment of the second aspect; the switching device and the inverter device are communicatively connected via the power connection line.

[0013] The fifth aspect of this application provides a computer-readable storage medium storing a computer program, which is loaded by a processor to execute the disconnection detection method of a multi-battery pack system described in the first aspect or any embodiment of the first aspect.

[0014] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments or exemplary technologies of this application, the accompanying drawings used in the description of the embodiments or exemplary technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0016] Figure 1 is a schematic diagram of the power supply system provided in an embodiment of this application.

[0017] Figure 2 is a schematic diagram of a power supply system provided in another embodiment of this application.

[0018] Figure 3 is a flowchart of an off-grid / on-grid switching control method provided in an embodiment of this application.

[0019] Figure 4 is another flowchart of the off-grid / on-grid switching control method provided in the embodiments of this application.

[0020] Figure 5 is another flowchart of the off-grid / on-grid switching control method provided in the embodiments of this application.

[0021] Figure 6 is a schematic diagram showing the relationship between grid voltage, power connection line signal, inverter voltage and inverter operating mode when the switching device adopts the off-grid switching method of the present application embodiment.

[0022] Figure 7 is a schematic diagram of the switching device provided in an embodiment of this application.

[0023] Figure 8 is a schematic diagram of a switching device provided in another embodiment of this application.

[0024] Figure 9 is a schematic diagram of the inverter device provided in an embodiment of this application. Detailed Implementation

[0025] It should be noted that the terms "first" and "second" in the specification, claims and drawings of this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0026] It should also be noted that the methods disclosed in the embodiments of this application or the methods shown in the flowcharts include one or more steps for implementing the method. Without departing from the scope of the claims, the execution order of multiple steps can be interchanged, and some steps can also be deleted.

[0027] Some embodiments will now be described with reference to the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] Inverters in energy storage systems can operate both off-grid with load and grid-connected. When operating off-grid with load, the control strategy for switching from off-grid to grid-connected operation can be activated once the grid returns to normal. Conversely, during grid-connected operation, the control strategy for switching from grid-connected to off-grid operation can be activated if the grid experiences a power outage. A controllable switching device is required between the inverter and the grid to ensure system safety. When the inverter and switching device are independent components, both contain controllers and require information exchange for off-grid / grid switching. In such cases, multiple communication lines are typically used between the inverter and switching device for information exchange, making the process complex. Therefore, simplifying the information exchange between the inverter and switching device, and achieving rapid switching between on-grid and off-grid operation for the inverter, are pressing issues that need to be addressed in this field.

[0029] Therefore, this application proposes an off-grid switching control method, a switching device, an inverter, and a power supply system, which can effectively reduce the number of connection lines between the switching device and the inverter, and realize rapid on-grid switching of the inverter.

[0030] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings.

[0031] Specifically, please refer to Figure 1, which shows a schematic diagram of the power supply system 10 provided in this embodiment of the application. As shown in Figure 1, the power supply system 10 includes an inverter 100, a switching device 200, and a power connection line 300. The output interface 101 of the inverter 100 is used to connect the first interface 201 of the switching device 200 and the load 20, and the second interface 202 of the switching device 200 is used to connect to the power grid 30. The switching device 200 and the inverter 100 are communicatively connected through the power connection line 300.

[0032] The inverter 100 can operate in grid-connected or off-grid mode based on the signal transmitted by the power connection line 300. The power connection line 300 can be a hard wire, that is, a connection line for transmitting level signals.

[0033] The input interface 102 of the inverter 100 can be connected to a photovoltaic module (not shown) or an energy storage battery (not shown). The photovoltaic module or energy storage battery provides DC power to the inverter 100, which converts the DC power into AC power and outputs it through the output interface 101 to power at least the load 20. In some other embodiments, the input interface 102 of the inverter 100 can also be connected to both a photovoltaic module and an energy storage battery.

[0034] A photovoltaic module includes a single photovoltaic panel (not shown in the figure), or multiple photovoltaic panels connected in series, parallel, or series-parallel configurations, without limitation. Under constant environmental conditions such as temperature and light intensity, the photovoltaic module can be used to generate photovoltaic power, producing DC power. An energy storage battery may include a battery pack (not shown in the figure), or multiple battery packs connected in series, parallel, or series-parallel configurations, without limitation. The energy storage battery can be charged by the inverter 100 and / or the photovoltaic module, and can also be used to output DC power to the inverter 100.

[0035] In some embodiments, the inverter 100 may include a Maximum Power Point Tracking (MPPT, not shown) circuit and a power conversion circuit 210 (as shown in FIG. 9). The input terminal of the MPPT circuit is connected to the output terminal of the photovoltaic module through the input interface 102 of the inverter 100. The output terminal of the MPPT circuit is connected to the DC side of the power conversion circuit 210. The AC side of the power conversion circuit 210 is connected to the output interface 101 of the inverter 100 to connect the load 20 and the switching device 200. The MPPT circuit can be used to perform maximum power point tracking on the photovoltaic module. The power conversion circuit 210 can be used to implement a direct current to alternating current (DC-AC, also known as inversion) function, or an alternating current to direct current (AC-DC, also known as rectification) function. The power conversion circuit 210 can output power to the load 20 through the output interface 101, or can receive power provided by the grid 30 through the output interface 101. The MPPT circuit can be, for example, a boost circuit, and the power conversion circuit 210 can be, for example, a full-bridge inverter circuit or a half-bridge inverter circuit. It is understood that, in one embodiment, the MPPT circuit can also be set independently of the inverter 100. The load 20 can be, for example, various AC loads in a household. The power grid 30 can be, for example, a mains power grid, a local power grid, or a microgrid.

[0036] Referring to Figure 2, in some embodiments, the power supply system 10 may further include a communication connection line 400. The communication connection line 400 also connects the switching device 200 and the inverter 100, allowing them to exchange information. For example, the switching device 200 can send grid voltage amplitude information to the inverter 100 via the communication connection line 400.

[0037] The communication connection cable 400 can be a communication bus, such as CAN (Controller Area Network) bus, RS485 bus, etc.

[0038] Please refer to Figure 3, which shows a schematic flowchart of the off-grid / on-grid switching control method provided in this embodiment of the application. The off-grid / on-grid switching control method provided in this embodiment of the application is applied to the switching device 200 in the power supply system 10 described above.

[0039] As shown in Figure 3, the off-grid and grid-connected switching control method includes the following steps S310-S320.

[0040] S310. When the grid supplies power, a first signal is sent to the inverter via the power connection line.

[0041] The first signal is used to indicate that the inverter 100 operates in grid-connected mode. When the grid 30 supplies power, the switching device 200 sends the first signal to the inverter 100 through the power connection line 300, and the inverter 100 can operate in grid-connected mode according to the first signal. During the period when the grid 30 supplies power, the switching device 200 can continuously send the first signal to the inverter 100 through the power connection line 300.

[0042] In some embodiments, the first signal can be a low-level signal. When the inverter 100 receives a low-level signal sent by the power connection line 300, the inverter 100 operates in grid-connected mode.

[0043] Of course, in some other embodiments, the first signal can also be a high-level signal, in which case the inverter 100 operates in grid-connected mode when it receives a high-level signal sent by the power connection line 300.

[0044] In some embodiments, the first signal may also be a level signal with a preset voltage amplitude, such as a 12V voltage signal or a 15V voltage signal.

[0045] Alternatively, in some other embodiments, the first signal may also be a triangular wave signal, a sine wave signal, or other types of signals, which are not limited in this application.

[0046] S320. When the power grid fails, the control switch is disconnected and a second signal is sent to the inverter via the power connection line.

[0047] The second signal has a different waveform from the first signal. The second signal is used to instruct the inverter 100 to switch its operating mode from grid-connected mode to off-grid mode and to operate according to the signal frequency and signal phase corresponding to the second signal.

[0048] When the power grid 30 loses power, the switch 200 opens and sends a second signal to the inverter 100 via the power connection line 300. The inverter 100 then switches from grid-connected mode to off-grid mode based on the second signal.

[0049] The inverter 100 operates according to the signal frequency and signal phase corresponding to the second signal. This can mean that the inverter 100 generates a control signal for the power conversion circuit 210 according to the signal frequency and signal phase corresponding to the second signal. This control signal is used to control the power conversion circuit 210 to output an inverter voltage, so that the frequency of the inverter voltage is the same as the signal frequency of the second signal, and the inverter phase of the inverter voltage is the same as the signal phase of the second signal.

[0050] It is understood that the signal frequency and signal phase of the second signal can be determined by the switching device 200 based on the grid voltage and grid frequency before the grid 30 is de-energized, or by the switching device 200 based on the operating frequency required by the load 20, or based on a preset power frequency, etc. This application does not limit this.

[0051] In this embodiment, when the power grid 30 supplies power, the switching device 200 sends a first signal to the inverter 100 via the power connection line 300, causing the inverter 100 to operate in grid-connected mode according to the first signal. When the power grid 30 loses power, the switching device 200 disconnects, breaking the connection between the output interface 101 of the inverter 100 and the power grid 30. Furthermore, the switching device 200 sends a second signal to the inverter 100 via the power connection line 300, causing the inverter 100 to switch its operating mode from grid-connected to off-grid mode according to the second signal, and operates according to the signal frequency and phase corresponding to the second signal, achieving rapid grid-connected / off-grid switching of the inverter 100. Since the waveforms of the first and second signals are different, the switching device 200 and the inverter 100 can transmit the first and second signals through the same power connection line 300, thereby reducing the number of connection lines between the switching device 200 and the inverter 100.

[0052] In some embodiments, the second signal may be a pulse signal, and the starting voltage of the second signal is different from the voltage of the first signal. Therefore, when the waveform of the signal received by the inverter 100 from the power connection line 300 is different from the waveform of the first signal, the inverter 100 switches from grid-connected mode to off-grid mode accordingly.

[0053] For example, when the first signal is a low-level signal and the grid 30 is supplying power, the switching device 200 outputs a low-level signal to the inverter 100 through the power connection line 300, and the inverter 100 operates in grid-connected mode. Then, if the grid 30 loses power, the switching device 200 disconnects, and the switching device 200 needs to switch the signal output to the power connection line 300 from the first signal to the second signal. At this time, the switching device 200 can generate the second signal according to a determined signal frequency and signal phase. The second signal is a pulse signal, starting with a rising edge, and is sent to the inverter 100 through the power connection line 300. When the signal received by the inverter 100 through the power connection line 300 changes from a low-level signal to a rising edge signal, this rising edge signal serves as an off-grid switching command for the inverter 100. The inverter 100 switches from grid-connected mode to off-grid mode according to the off-grid switching command. Afterward, the inverter 100 operates according to the signal frequency and signal phase of the received second signal.

[0054] For example, when the first signal is a high-level signal, the switching device 200 can generate a second signal based on a determined signal frequency and phase when the power grid 30 fails. The second signal is a pulse signal, starting with a falling edge, and is sent to the inverter 100 via the power connection line 300. When the signal received by the inverter 100 through the power connection line 300 changes from a high-level signal to a falling edge signal, this falling edge signal serves as an off-grid switching command for the inverter 100. The inverter 100 then switches from grid-connected mode to off-grid mode according to this command. Afterward, the inverter 100 operates based on the signal frequency and phase of the received second signal.

[0055] In some embodiments, the initial value of the signal frequency of the second signal is a preset power frequency. For example, the preset power frequency can be 50Hz, 60Hz, etc.

[0056] In some embodiments, the initial value of the signal frequency of the second signal can be determined by the switching device 200 based on the grid frequency of the grid voltage before the power grid 30 is de-energized. Thus, when the power grid 30 is de-energized, since the inverter 100 operates according to the signal frequency and phase corresponding to the second signal, the frequency and phase of the output voltage at the moment the inverter 100 switches from grid-connected mode to off-grid mode are synchronized with the signal frequency and phase of the second signal, and further synchronized with the grid frequency and phase of the grid voltage when the power grid 30 is not de-energized. This achieves a seamless switching of the inverter 100 from grid-connected mode to off-grid mode.

[0057] It is understood that when the inverter 100 receives an off-grid switching command through the power connection line 300, the inverter 100 can perform voltage source inverter control output according to the preset off-grid rated voltage, and after determining the signal frequency and signal phase of the second signal, it can operate according to the signal frequency and signal phase of the second signal. The off-grid rated voltage is a value preset in the inverter 100, which can be determined according to the needs of the actual scenario and relevant regulations.

[0058] In some embodiments, if multiple inverters 100 are connected in parallel in the power supply system 10, each inverter 100 is connected to the switching device 200 via a power connection line 300. When the power grid 30 fails, the second signal can serve as a synchronization signal for the off-grid operation of the multiple inverters 100. Each inverter 100 can perform phase-locked synchronization based on the received second signal and be controlled according to the output power of each inverter 100, thereby realizing the off-grid operation of the multiple inverters 100.

[0059] Please refer to Figure 4. In some embodiments, the off-grid / on-grid switching control method may further include:

[0060] S410. When the power grid is restored from power failure to power supply, the signal phase of the second signal is adjusted according to the power grid phase of the power grid voltage until the signal phase is consistent with the power grid phase.

[0061] When the power grid 30 is restored from a power outage, the grid phase of the grid voltage and the inverter phase of the inverter voltage output by the inverter 100 may be out of sync. Since the inverter 100 operates based on the signal frequency and phase of the second signal, the switching device 200 can adjust the signal phase of the second signal to match the grid phase, thereby ensuring that the inverter phase of the inverter voltage output by the inverter 100 also follows the signal phase change of the second signal to match the grid phase, thus achieving grid pre-synchronization of the inverter 100.

[0062] The switching device 200 can fine-tune the signal frequency of the second signal multiple times, so that the signal phase of the second signal changes slowly until the signal phase is adjusted to match the phase of the power grid.

[0063] It is understood that the switching device 200 can obtain the grid phase based on the grid voltage transmitted from the grid 30 to the second interface 202. For example, a grid voltage detection circuit (not shown) can be provided in the switching device 200. The grid voltage detection circuit can be connected to the first interface 201 of the switching device 200 to detect the grid voltage. The control circuit can obtain the grid voltage through the grid voltage detection circuit, then obtain the grid phase based on the grid voltage, and then adjust the signal phase of the second signal according to the obtained grid phase. Of course, the grid voltage detection circuit can also be set independently of the switching device 200.

[0064] S420, Detect the inverter phase of the inverter voltage output by the inverter device.

[0065] Similarly, the switching device 200 can also obtain the inverter phase based on the inverter voltage output by the inverter device 100. For example, an inverter voltage detection circuit (not shown) can be provided in the switching device 200. The inverter voltage detection circuit can be connected to the first interface 201 of the switching device 200 to detect the inverter voltage output by the inverter device 100. The control circuit can obtain the inverter voltage through the inverter voltage detection circuit and then obtain the inverter phase based on the inverter voltage. Of course, the inverter voltage detection circuit can also be set independently of the switching device 200.

[0066] S430. When the inverter phase is consistent with the grid phase, a closing notification signal is sent to the inverter device through the communication connection line.

[0067] When the switching device 200 detects that the inverter 100 has adjusted its inverter phase to match the grid phase according to the adjusted second signal, the inverter 100's operating mode can seamlessly switch from off-grid mode to grid-connected mode, thus enabling the switching device 200 to conduct. Before the switching device 200 conducts, it can send a closing notification signal to the inverter 100 via the communication connection line 400 to inform the inverter 100 that it is about to connect to the grid 30.

[0068] S440: The control switch is turned on and sends a first signal to the inverter via the power connection line.

[0069] The switching device 200 is turned on and sends a first signal to the inverter 100 through the power connection line 300. Upon receiving the first signal, the inverter 100 confirms that the switching device 200 is turned on, and its operating mode switches from off-grid mode to grid-connected mode. Because the inverter 100 has pre-synchronized with the grid 30 according to the second phase, it can achieve a seamless switch from off-grid mode to grid-connected mode when the switching device 200 is turned on.

[0070] In some embodiments, the off-grid switching control method may further include: sending grid voltage amplitude information to the inverter 100 via a communication connection line 400.

[0071] It is understandable that when the switching device 200 detects that the power grid 30 has been restored from power failure to power supply, in addition to sending the second signal adjusted according to the power grid phase to the inverter device 100 in real time through the power connection line 300, it can also send the amplitude information of the power grid voltage to the inverter device 100 through the communication connection line 400. This allows the inverter device 100 to adjust its inverter voltage according to the amplitude information and the phase of the second signal, so that the amplitude of the inverter voltage is consistent with the amplitude of the power grid voltage and the inverter phase is consistent with the phase of the power grid, thereby achieving pre-synchronization of the inverter device 100 with the power grid 30.

[0072] Correspondingly, step S430 includes: when the inverter phase is consistent with the grid phase and the amplitude information of the inverter voltage is consistent with the amplitude information of the grid voltage, sending a closing notification signal to the inverter device 100 through the communication connection line 400.

[0073] Therefore, in step S440, before the switching device 200 is turned on, the inverter device 100 has already adjusted the inverter voltage to match the grid phase based on the phase of the second signal and the amplitude phase of the grid voltage, and the amplitude information of the inverter voltage is consistent with the amplitude information of the grid voltage. Therefore, when the switching device 200 is turned on, the inverter voltage of the inverter device 100 can be directly connected to the grid 30, and the voltage difference between the two ends of the switching device 200 is very small, which can effectively achieve seamless switching from off-grid mode to grid-connected mode.

[0074] In this embodiment, during the process of the switching device 200 executing steps S410 to S440, the inverter device 100 is in the pre-synchronization process before grid connection. Therefore, this process can be considered as the working mode of the inverter device 100 being the off-grid pre-synchronization mode.

[0075] Please refer to Figure 5. In some embodiments, the off-grid / on-grid switching control method may further include:

[0076] S510: Sends an islanding detection command to the inverter via the communication connection line.

[0077] The islanding detection command is used to instruct the inverter 100 to output reactive power through the output interface 101. When the grid 30 supplies power, the switch 200 sends the islanding detection command to the inverter 100 through the communication connection line 400, and the inverter 100 outputs reactive power to the output interface 101 according to the islanding detection command.

[0078] S520. Confirm whether the power grid is down based on the electrical parameters of the first interface.

[0079] After the switching device 200 sends an islanding detection command through the communication connection line 400, the switching device 200 detects the electrical parameters of its first interface 201 and confirms whether islanding has occurred at the first interface 201 based on the electrical parameters, thereby realizing islanding detection of the first interface 201. When the first interface 201 sends an islanding signal, it can be confirmed that the power grid 30 has lost power.

[0080] It should be noted that the islanding phenomenon refers to a situation where, when the power grid 30 loses power, the inverter 100 continues to supply power to the adjacent lines in the power grid 30.

[0081] In some embodiments, electrical parameters may include the voltage amplitude or voltage frequency of the load 20 connected to the first interface 201. When the power grid 30 is de-energized, the change in reactive power output by the inverter 100 will affect the voltage frequency of the load 20 connected to the first interface 201. Alternatively, when the power grid 30 is de-energized, the reactive power output by the inverter 100 will affect the stability of the voltage amplitude of the load 20 connected to the first interface 201. Therefore, the switching device 200 can determine whether the power grid 30 is de-energized by detecting the voltage amplitude or voltage frequency of the first interface 201. In this case, the switching device 200 may be equipped with a detection circuit 230 (as shown in FIG8), which detects the voltage of the first interface 201, determines the voltage amplitude or voltage frequency based on the detected voltage, and then determines whether the power grid 30 is de-energized based on the voltage amplitude or voltage frequency.

[0082] When the inverter 100 outputs reactive power and the grid 30 loses power, the active and reactive power output by the inverter 100 will no longer be balanced with the power consumed by the load 20. The switching device 200 can determine whether the grid 30 has lost power by detecting this imbalance. Therefore, in some specific examples, the electrical parameters may also include the active and reactive power output by the inverter 100 and the reactive and active power of the load 20 connected to the first interface 201. At this time, the switching device 200 may be equipped with a detection circuit 230 (as shown in Figure 8) to detect the voltage and current of the first interface 201. Based on the detected voltage and current, the reactive and active power of the load 20 are determined, and then the grid 30 is determined to have lost power based on the reactive and active power. At the same time, the inverter 100 can also send its output active and reactive power information to the switching device 200 via the communication connection line 400, so that the switching device 200 can determine whether the active and reactive power of the load 20 and the inverter 100 are balanced.

[0083] It is understood that the switching device 200 dispatches the inverter 100 to output reactive power to the output interface 101 via the communication connection line 400 to achieve islanding detection. The switching device 200 can employ any detection method from relevant islanding detection technologies, or other detection methods, to detect power outages; the specific process is not limited to the aforementioned specific example.

[0084] For example, in some embodiments, the switching device 200 can perform islanding detection by scheduling the active power output of the inverter 100 through the communication connection line 400. In other embodiments, the switching device 200 can also perform power failure detection by detecting the effective value of the grid voltage, etc. This application does not limit this.

[0085] Next, the off-grid / in-grid switching method provided in this application embodiment will be described in detail with specific example scenarios.

[0086] Please refer to Figure 6, which shows a schematic diagram of the relationship between the grid voltage, the signal of the power connection line 300, the inverter voltage and the operating mode of the inverter device 100 when the switching device 200 adopts the off-grid switching method of the present application embodiment.

[0087] As shown in time period ① of Figure 6, when the grid 30 starts supplying power but the inverter 100 has not yet started working, the switching device 200 detects the power supply from the grid 30, turns on, and sends a high-level signal (first signal) to the inverter 100 through the power connection line 300. The inverter 100 operates in grid-connected mode according to the first signal sent by the power connection line 300, and performs phase-locking on the grid voltage / current, operating according to the detected grid phase.

[0088] During the period when the power grid 30 is supplying power, the switchgear 200 can also send an islanding detection command to the inverter 100 via the communication connection line 400. The inverter 100 outputs the corresponding reactive power based on the islanding detection command. The switchgear 200 detects whether the power grid 30 has lost power by detecting the electrical parameters of the first interface 201.

[0089] During time period ② as shown in Figure 6, when the power grid 30 experiences a power outage, the switching device 200 detects the outage and automatically disconnects, sending a second signal to the inverter 100 via the power connection line 300. This second signal is a pulse signal, starting with a falling edge (as shown by the falling arrow in Figure 6). This falling edge signal serves as the off-grid switching command for the inverter 100. Based on the off-grid switching command, the inverter 100 switches from grid-connected mode to off-grid mode, and performs voltage source inverter control output based on the off-grid rated voltage.

[0090] Then, during time period ③ as shown in Figure 6, the inverter 100 outputs an inverter voltage according to the signal frequency of the second signal, so that the inverter phase of the inverter voltage is synchronized with the signal phase of the second signal, and the inverter 100 operates in off-grid mode.

[0091] During time period ④ of Figure 6, the power grid 30 recovers from a power outage. The switching device 200 can then confirm the recovery of power supply by detecting the voltage at its second interface 202. The switching device 200 first adjusts the signal phase of the second signal according to the power grid phase until the signal phase matches the power grid phase. The inverter 100 adjusts the inverter phase of its inverter voltage in real time according to the adjusted second signal, gradually adjusting the inverter phase to match the power grid phase. Furthermore, the switching device 200 can also send the amplitude information of the power grid voltage to the inverter 100 via the communication connection line 400, causing the inverter 100 to simultaneously adjust its inverter voltage amplitude information to match the power grid voltage amplitude information. During this process, the inverter 100 is in an off-grid pre-synchronization mode.

[0092] As shown in Figure 6, at the boundary between time periods ④ and ⑤, when the switching device 200 detects that the inverter phase is consistent with the grid phase and the amplitude information of the inverter voltage is consistent with the amplitude information of the grid voltage, the switching device 200 sends a closing notification signal to the inverter 100 through the communication connection line 400. The switching device 200 is turned on and outputs a high-level signal (first signal) to the inverter 100 through the power connection line 300. The inverter 100 confirms that the switching device 200 is turned on based on the high-level signal, and the inverter 100 enters the grid-connected mode, realizing the switch from off-grid mode to grid-connected mode. Afterwards, the inverter 100 operates in grid-connected mode (as shown in Figure 6, time period ⑤).

[0093] It is understood that Figure 6 is only a specific example, and the off-grid and on-grid switching control method of this application embodiment is not limited thereto.

[0094] It should be noted that, for the sake of simplicity, the aforementioned method embodiments are described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps may be performed in other orders or simultaneously.

[0095] Please refer to Figure 7, which shows a schematic diagram of the switching device 200 provided in an embodiment of this application. As shown in Figure 7, the switching device 200 includes a switching circuit 210 and a control circuit 220. The switching circuit 210 is connected between the first interface 201 and the second interface 202, and is used to disconnect or break the connection between the first interface 201 and the second interface 202.

[0096] For example, the switching circuit 210 may include, but is not limited to, controllable switches such as transistors, metal-oxide-semiconductor field-effect transistors (MOS), insulated-gate bipolar transistors (IGBTs), optocouplers, and relays.

[0097] Control circuit 220 connects switching circuit 210 and power connection line 300. When the grid 30 supplies power, control circuit 220 sends a first signal to inverter 100 via power connection line 300. The first signal indicates that inverter 100 operates in grid-connected mode. When the grid 30 loses power, control circuit 220 controls switching circuit 210 to disconnect and sends a second signal to inverter 100 via power connection line 300. The second signal has a different waveform than the first signal. The second signal indicates that inverter 100 switches its operating mode from grid-connected mode to off-grid mode, and operates according to the signal frequency and phase corresponding to the second signal.

[0098] It is understood that the control circuit 220 can be used to execute the aforementioned grid-connected / off-grid switching control method. The control circuit 220 may include a microcontroller unit (MCU), a control chip, etc.

[0099] Furthermore, as shown in Figure 8, the switching device 200 may also include a detection circuit 230, which is used to detect whether the power grid 30 has lost power. The specific method by which the detection circuit 230 detects whether the power grid 30 has lost power can be found in the aforementioned description of the grid-connected / off-grid switching method, and will not be repeated here.

[0100] It is understood that the beneficial effects and specific implementation methods of the switching device 200 provided in this application embodiment can be referred to the beneficial effects of the corresponding off-grid and on-grid switching control methods provided above, and will not be repeated here.

[0101] Please refer to Figure 9, which shows a schematic diagram of the inverter device 100 provided in an embodiment of this application. As shown in Figure 8, the inverter device 100 includes a power conversion circuit 210 and a main control circuit 120.

[0102] The power conversion circuit 210 outputs and / or receives power through the output interface 101. The specific implementation of the power conversion circuit 210 outputting and receiving power through the output interface 101 can be found in the aforementioned description of the power supply system 10, and will not be repeated here.

[0103] The main control circuit 120 connects the power connection line 300 and the power conversion circuit 210. The main control circuit 120 is used to monitor the signals transmitted on the power connection line 300.

[0104] When the first signal transmitted through the power connection line 300 is detected, the main control circuit 120 controls the power conversion circuit 210 to operate in grid-connected mode. When the signal transmitted through the power connection line 300 changes from the first signal to the second signal, the main control circuit 120 switches the operating mode of the power conversion circuit 210 from grid-connected mode to off-grid mode, and operates according to the signal frequency and signal phase corresponding to the second signal.

[0105] It is understood that the beneficial effects and specific implementation methods of the inverter device 100 provided in this application embodiment can be referred to the beneficial effects of the corresponding grid-connected / off-grid switching control method provided above, and will not be repeated here.

[0106] This application also provides a computer-readable storage medium for storing computer programs or code, which, when loaded and executed by a processor, implement all or part of the steps in the off-grid / parallel switching control method embodiments shown in Figures 3 to 5 above.

[0107] Computer-readable storage media include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules or other data). Computer-readable storage media include, but are not limited to, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tapes, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and is accessible to a computer.

[0108] The computer-readable storage medium can be an internal storage unit of the switching device 200 described in the foregoing embodiments, such as a hard disk or memory inside the switching device 200. Further, the computer-readable storage medium may mainly include a program storage area and a data storage area, wherein the program storage area may store the operating system, programs required for at least one function, etc., and the data storage area may store data created according to each program, etc.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A grid-connected / off-grid switching control method, applied to a switching device in a power supply system, the power supply system including an inverter, a switching device, and a power connection line, wherein the output interface of the inverter is configured to connect to a first interface of the switching device and a load, the second interface of the switching device is configured to connect to the power grid, and the switching device and the inverter are communicatively connected through the power connection line; The off-grid / on-grid switching control method includes: When the grid supplies power, a first signal is sent to the inverter via the power connection line. The first signal is configured to indicate that the inverter is operating in grid-connected mode. When the power grid fails, the control switch is disconnected and a second signal is sent to the inverter via the power connection line. The second signal has a different waveform from the first signal. The second signal is configured to instruct the inverter to switch its operating mode from the grid-connected mode to the off-grid mode and to operate according to the signal frequency and signal phase corresponding to the second signal.

2. The off-grid / on-grid switching control method as described in claim 1, wherein, A communication connection line is connected between the switching device and the inverter device; the method further includes: When the power grid is restored from a power outage to a power supply, the signal phase of the second signal is adjusted according to the power grid phase of the power grid voltage until the signal phase is consistent with the power grid phase; Detect the inverter phase of the inverter voltage output by the inverter device; When the inverter phase is consistent with the grid phase, a closing notification signal is sent to the inverter device through the communication connection line; The switching device is turned on, and the first signal is sent to the inverter through the power connection line.

3. The off-grid / on-grid switching control method as described in claim 2, wherein, The method further includes: The amplitude information of the grid voltage is sent to the inverter via the communication connection line; Accordingly, when the inverter phase is consistent with the grid phase, sending a closing notification signal to the inverter device through the communication connection line includes: When the inverter phase is consistent with the grid phase, and the amplitude information of the inverter voltage is consistent with the amplitude information of the grid voltage, a closing notification signal is sent to the inverter device through the communication connection line.

4. The off-grid / on-grid switching control method as described in claim 1, wherein, A communication connection line is connected between the switching device and the inverter device; the method further includes: An islanding detection command is sent to the inverter via the communication connection line. The islanding detection command is configured to instruct the inverter to output reactive power through the output interface. The power grid status is confirmed based on the electrical parameters of the first interface.

5. The off-grid / on-grid switching control method as described in claim 1, wherein, The first signal is a low-level signal or a high-level signal, the second signal is a pulse signal, and the starting voltage of the second signal is different from the voltage of the first signal; and / or The initial value of the signal frequency of the second signal is a preset power frequency.

6. A switching device, disposed in a power supply system, the power supply system further comprising an inverter and a power connection line, wherein the output interface of the inverter is configured to connect a first interface of the switching device and a load, a second interface of the switching device is configured to connect to a power grid, and the switching device is communicatively connected to the inverter via the power connection line; the switching device comprises: A switching circuit configured to disconnect or connect the connection between the first interface and the second interface; A control circuit, connected to the switching circuit and the power connection line, is configured to: When the grid supplies power, a first signal is sent to the inverter via the power connection line. The first signal is configured to indicate that the inverter is operating in grid-connected mode. When the power grid fails, the control switch circuit is disconnected, and a second signal is sent to the inverter through the power connection line. The second signal has a different waveform from the first signal. The second signal is configured to instruct the inverter to switch its operating mode from the grid-connected mode to the off-grid mode, and to operate according to the signal frequency and signal phase corresponding to the second signal.

7. The switching device as claimed in claim 6, wherein, It also includes a detection circuit connected to the control circuit, the detection circuit being configured to detect whether the power grid has lost power.

8. The switching device as claimed in claim 6 or 7, wherein, The power supply system also includes a communication connection line, through which the control circuit is communicatively connected to the inverter.

9. An inverter device disposed in a power supply system, the power supply system further comprising a switching device and a power connection line, wherein the output interface of the inverter device is configured to connect to a first interface of the switching device and a load, a second interface of the switching device is configured to connect to a power grid, and the inverter device is communicatively connected to the switching device via the power connection line; the inverter device comprises: A power conversion circuit that outputs and / or receives power through the output interface; The main control circuit, which is connected to the power connection line and the power conversion circuit, is configured as follows: Monitor the signals transmitted on the power connection line; Upon detecting the first signal transmitted by the power connection line, the power conversion circuit is controlled to operate in grid-connected mode; When the signal transmitted by the power connection line is detected to change from the first signal to the second signal, the operating mode of the power conversion circuit is switched from the grid-connected mode to the off-grid mode, and the circuit operates according to the signal frequency and signal phase corresponding to the second signal; wherein the second signal has a different waveform from the first signal.

10. A power supply system comprising an inverter as described in claim 9, a power connection line, and a switching device as described in any one of claims 6-8; wherein the switching device and the inverter are communicatively connected via the power connection line.

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