Power supply system, grid-connected-to-off-grid control method for power supply system and inverter

Abstract

The embodiment of the invention provides a power supply system, a grid-connected-to-off-grid control method for the power supply system and an inverter. The power supply system comprises an inverter and a grid-connected and off-grid controller. The direct current end and the alternating current end of the inverter are connected with a direct current power source and an inversion port of the grid-connected and off-grid controller respectively. The standby power port of the grid-connected and off-grid controller is used for being connected with a standby power load, the power grid port of the grid-connected and off-grid controller is used for being connected with a power grid, the standby power port is connected with the inversion port, and the inversion port is connected with the power grid port through the relay. And after detecting that the power grid stops supplying power to the standby power load, the inverter stops outputting the alternating current. The control chip of the grid-connected and off-grid controller is used for controlling the relay to be disconnected when the inverter stops outputting the alternating current or when the instantaneous value of the grid voltage exceeds a set voltage interval, and outputting a low-level signal or a high-level signal to the inverter through a hardware signal line at the same time, so that the inverter switches a voltage source control mode. And the output alternating current is recovered to supply power to the standby power load.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to a power supply system, a grid-connection and grid-disconnection control method for the power supply system, and an inverter. Background Art

[0002] With the development of the photovoltaic power generation industry, household green electricity solutions have gradually become more complete. In order to ensure the continuity and reliability of power supply to users' important loads, photovoltaic power inverters generally have on-grid and off-grid output functions. For the backup power system composed of on-grid and off-grid controllers and inverters, there are problems that need to be solved when switching from on-grid to off-grid, such as low accuracy of grid anomaly detection, inability to achieve seamless switching, and low power supply continuity for backup power loads. Summary of the invention

[0003] The present application provides a power supply system, a power supply system grid connection and disconnection control method and an inverter, which can avoid the inverter stopping working after detecting a grid fault first, and improve the power supply continuity to the backup power load during the grid connection and disconnection process.

[0004] In a first aspect, the present application provides a power supply system, which includes an inverter and an on-grid and off-grid controller, wherein the DC end of the inverter is used to connect a DC power supply, and the AC end of the inverter is connected to the inverter port of the on-grid and off-grid controller. The on-grid and off-grid controller includes a relay and a control chip, the backup power port of the on-grid and off-grid controller is used to connect a backup power load, and the grid port of the on-grid and off-grid controller is used to connect a grid, wherein the backup power port is connected to the inverter port, and the inverter port and the grid port of the on-grid and off-grid controller are connected via a relay. The inverter is used to convert direct current from a DC power supply into alternating current when it is in a current source control mode and the relay is closed, and the inverter or the grid is used to jointly supply power to the backup power load. The inverter is also used to suspend the output of alternating current after detecting that the grid stops supplying power to the backup power load. The control chip is used to control the relay to disconnect when the inverter stops outputting AC power, or when the instantaneous value of the grid voltage exceeds the set voltage range, and at the same time output a low-level signal or a high-level signal to the inverter through the hardware signal line, so that the inverter switches to the voltage source control mode and converts the DC power from the DC power supply into AC power to supply power to the backup load.

[0005] In this embodiment, the control chip can detect the grid voltage abnormality before the inverter by detecting the instantaneous value of the grid voltage, thereby avoiding the inverter from stopping working after detecting the grid fault first, and improving the power supply continuity to the backup power load. When the control chip disconnects the relay, it outputs a low-level signal to the inverter through the hardware signal line. The transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the low-level signal, so that the inverter can quickly switch to the voltage source control mode to supply power to the backup power load, further improving the power supply continuity to the backup power load during the grid connection and disconnection process, and realizing the seamless switching of the inverter from grid connection to grid connection. In addition, during the grid connection operation of the inverter, the inverter detects the grid voltage in the island operation mode, and when it detects that the grid stops supplying power to the backup power load, the wave is blocked, so that the control chip in the grid connection and disconnection controller can sense the power failure of the grid voltage, thereby smoothly realizing the grid connection and disconnection.

[0006] In a possible implementation, the inverter is used to send out an alarm signal and shut down after suspending the output of AC power for a period of time exceeding a first preset time interval. The inverter detects that the grid stops supplying power to the backup load and blocks the wave. If the on-grid and off-grid controller has not sent a low-level signal to the inverter after the first preset time interval, the on-grid and off-grid controller is working abnormally. In order to enable the inverter to continue to supply power to the backup load in the environment of a grid failure, the inverter sends out an alarm signal and shuts down for the next off-grid startup.

[0007] In a possible implementation, the control chip is used to control the relay to disconnect after the grid voltage amplitude exceeds the set voltage interval and exceeds the second preset time interval, and at the same time output a low-level signal or a high-level signal to the inverter through the hardware signal line. After determining that a grid fault occurs, the control chip controls the relay to disconnect, and outputs a low-level signal or a high-level signal to the inverter through the hardware signal line, so that the inverter quickly switches to the voltage source control mode to supply power to the backup load, thereby improving the power supply continuity to the backup load during the grid connection and disconnection process.

[0008] In a possible implementation, the relay includes a first relay and a second relay connected in series, the first relay is connected to the inverter port, the second relay is connected to the grid port, and the disconnection speed of the first relay is greater than the disconnection speed of the second relay. Since the disconnection speed of the first relay is greater than the disconnection speed of the second relay, the first relay can switch from closed to open more quickly, thereby ensuring rapid disconnection of the inverter and the grid side.

[0009] In one possible implementation, the power supply system includes multiple inverters, and the AC ends of the multiple inverters are connected in parallel and then connected to the inverter port of the on-grid and off-grid controller through the grid connection point. The control chip is used to control the relay to disconnect when the grid connection point suspends the output of AC power, or when the instantaneous value of the grid voltage exceeds the set voltage range, and at the same time outputs a low-level signal or a high-level signal to the multiple inverters through the hardware signal line, so that the multiple inverters switch to the voltage source control mode, and convert the DC power from the DC power supply into AC power to supply power to the backup power load. After determining that a fault has occurred in the grid, the control chip controls the relay to disconnect, and outputs a low-level signal or a high-level signal to the multiple inverters through the hardware signal line, so that the multiple inverters quickly switch to the voltage source control mode to supply power to the backup power load, thereby improving the power supply continuity to the backup power load during the grid connection and off-grid process.

[0010] In a possible implementation, the non-backup power port of the on-grid and off-grid controller is used to connect the non-backup power load, and the non-backup power port is connected to the grid port. The inverter is also used, in the current source control mode, for the inverter or the grid to jointly supply power to the backup power load and the non-backup power load.

[0011] In the second aspect, the present application provides a method for controlling the grid connection and disconnection of a power supply system, the method comprising: when the relay is closed and the inverter stops outputting AC power, or when the relay is closed and the instantaneous value of the grid voltage exceeds the set voltage range, controlling the relay to disconnect, and outputting a low-level signal or a high-level signal to the inverter through a hardware signal line, so that the inverter switches to a voltage source control mode. The DC end of the inverter is used to connect a DC power supply, and the AC end of the inverter is connected to the grid through a relay.

[0012] In this embodiment, by detecting the instantaneous value of the grid voltage, the grid voltage abnormality can be detected before the inverter, thereby avoiding the inverter stopping working after detecting the grid fault first, and improving the power supply continuity to the backup power load. When the relay is disconnected, a low-level signal is output to the inverter through the hardware signal line. The transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the low-level signal, so that the inverter can quickly switch to the voltage source control mode to supply power to the backup power load, and further improve the power supply continuity to the backup power load during the grid connection and disconnection process. In addition, the inverter blocks the wave when it detects that the grid stops supplying power to the backup power load in the island operation mode, so that the grid voltage can be sensed to achieve grid connection and disconnection smoothly.

[0013] In a possible implementation, the method further includes controlling the relay to disconnect after the relay is closed and the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, and outputting a low level signal or a high level signal to the inverter through a hardware signal line. After determining that a grid fault occurs, the relay is controlled to disconnect, and a low level signal or a high level signal is output to the inverter through a hardware signal line, so that the inverter quickly switches to a voltage source control mode to supply power to the backup load, thereby improving the power supply continuity to the backup load during the process of grid connection and disconnection.

[0014] In a third aspect, the present application provides an inverter, which includes an inverter circuit, a grid-connected relay and an off-grid relay, the DC end of the inverter is used to connect a DC power supply, the grid-connected port of the inverter is connected to the power grid, the off-grid port of the inverter is used to connect a backup power load, the output end of the inverter circuit is connected to the grid-connected port through the grid-connected relay, and the output end of the inverter circuit is connected to the off-grid port through the off-grid relay. The inverter is used to convert the DC power from the DC power supply into AC power when it is in the current source control mode and the off-grid relay is closed and the grid-connected relay is closed, and the inverter or the power grid is used to jointly supply power to the backup power load. The inverter is also used to control the grid-connected relay to disconnect when it is detected that the power grid stops supplying power to the backup power load, or when the instantaneous value of the power grid voltage exceeds the set voltage interval, or when the power grid voltage amplitude exceeds the set voltage interval and exceeds the second preset time interval, and at the same time switch the voltage source control mode to convert the DC power from the DC power supply into AC power to supply power to the backup power load.

[0015] In this embodiment, after detecting a grid abnormality or power failure, the inverter directly disconnects the grid-connected relay and switches to the voltage source mode, thereby improving the power supply continuity to the backup load. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of an application scenario of the power supply system provided by this application;

[0017] Figure 2 is a schematic diagram of another application scenario of the power supply system provided by the present application;

[0018] Figure 3 is a schematic diagram of another application scenario of the power supply system provided by the present application;

[0019] Figure 4 This is a hardware circuit diagram of an on-grid and off-grid controller provided by this application;

[0020] Figure 5 It is another hardware circuit diagram of the on-grid and off-grid controller provided by the present application;

[0021] Figure 6It is a flow chart of the grid connection and disconnection control method of the power supply system provided by the present application;

[0022] Figure 7 It is a schematic diagram of the application scenario of the inverter provided in this application. DETAILED DESCRIPTION

[0023] See also Figure 1 , Figure 1 It is a schematic diagram of an application scenario of the power supply system provided by the present application. The power supply system provided by the present application may include an inverter and an off-grid controller, wherein the DC end of the inverter is used to connect a DC power supply, and the AC end of the inverter is connected to the inverter port of the off-grid controller. Specifically, the DC power supply may be a photovoltaic string, and the inverter may include a DC conversion circuit and an inverter circuit, the input end of the DC conversion circuit is connected to the photovoltaic string, the output end of the DC conversion circuit is connected to the input end of the inverter circuit, and the output end of the inverter circuit is connected to the inverter port of the off-grid controller. The off-grid controller includes a relay and a control chip, and the backup power port and the non-backup power port of the off-grid controller are used to connect the backup power load and the non-backup power load, respectively, and the grid port of the off-grid controller is used to connect the grid, wherein the backup power port is connected to the inverter port, and the non-backup power port is connected to the grid port, and the inverter port and the grid port of the off-grid controller are connected through a relay.

[0024] here, Figure 1 In the power supply system shown, when the relay is closed and the inverter is connected to the grid, the inverter can boost the DC power provided by the photovoltaic array through the DC conversion circuit, and invert the boosted DC power through the inverter circuit. The AC power obtained after the inverter inverts or the AC power from the power grid can power the backup load and the non-backup load. When the relay is disconnected and the inverter is off-grid, the inverter can boost the DC power provided by the photovoltaic array through the DC conversion circuit, and invert the boosted DC power through the inverter circuit, so that the AC power obtained after the inversion conversion is output to the backup load for power supply, and the non-backup load is not powered. In the home power supply scenario, the above-mentioned backup load can be an important load in the user's home, such as household appliances, alarm equipment, etc., which will not be powered off even when the power grid is out of power. The above-mentioned non-backup load can be a non-important load in the user's home, such as a charging pile, etc., which will not be powered when the power grid is out of power, so as to ensure that the backup load can be powered for a longer time.

[0025] In some possible implementations, please refer again to Figure 1The DC power supply may also include an energy storage battery. The output end of the energy storage battery may be connected to the output end of the DC conversion circuit in the above-mentioned inverter. The energy storage battery may provide DC power to the above-mentioned inverter circuit. The inverter circuit inverts the DC power provided by the energy storage battery and outputs the AC power obtained after the inversion conversion to power the backup load and the non-backup load.

[0026] exist Figure 1 In the application scenario shown, during the inverter grid-connected operation, the grid-connected and off-grid controller detects the grid voltage through the control chip. If the grid voltage meets the grid-connected and off-grid conditions, the inverter is controlled to switch from grid-connected to off-grid. The current grid-connected and off-grid switching methods do not consider the power supply continuity of important loads such as backup loads, and the power supply reliability of backup loads is poor. In addition, if the current grid loses power and the inverter operates in island mode, the output power of the inverter is balanced and can meet the power demand of the load in the power supply system, resulting in the inability to detect abnormal voltage conditions on the grid side and the inability to smoothly achieve grid-connected and off-grid switching.

[0027] In the power supply system provided by the present application, during the inverter grid-connected operation, the relay in the grid-connected and off-grid controller is closed, and the inverter is in the current source control mode. During the grid-connected period, the inverter or the grid supplies power to the backup load and the non-backup load. For details, see again Figure 1, the relay in the on-grid and off-grid controller may include two relays, for example, it may include a first relay and a second relay connected in series (for the convenience of description, they may be respectively referred to as relay K1 and relay K2), the above relay K1 is connected to the inverter port, and relay K2 is connected to the grid port. During the grid-connected operation of the inverter, the relays K1 and K2 in the on-grid and off-grid controller are closed, the inverter is in the current source control mode and supplies power to the backup load and the non-backup load. The control chip in the on-grid and off-grid controller is used to, when the inverter is on-grid, when it is detected that the instantaneous value of the grid voltage exceeds the set voltage interval, determine that the current grid voltage is abnormal, and meet the conditions for grid-connection and off-grid disconnection, then control relays K1 and relays K2 to disconnect, and at the same time output a low-level signal or a high-level signal to the inverter through the hardware signal line, so that the inverter switches from the current source control mode to the voltage source control mode. For example, taking a low-level signal as an off-grid signal as an example, a low-level signal is output to the inverter through the hardware signal line so that the inverter switches to the voltage source control mode. During the off-grid period, the inverter only supplies power to the backup load. In addition, during the grid-connected operation of the above-mentioned inverter, if it enters the island operation mode, the inverter can detect the grid voltage. When it is detected that the grid stops supplying power to the backup load and the non-backup load, the inverter will block the wave and suspend the output of AC power. The control chip in the grid-connected and off-grid controller is also used to determine that the current grid voltage is powered off when the inverter is in the current source control mode, the relay is closed, and the inverter suspends the output of AC power, and meets the grid-connected and off-grid conditions, then control relays K1 and K2 to disconnect, and output a low-level signal to the inverter through the hardware signal line, so that the inverter switches from the current source control mode to the voltage source control mode. Here, the control chip can detect the grid voltage abnormality before the inverter by detecting the instantaneous value of the grid voltage, thereby avoiding the inverter from stopping working after detecting the grid fault first, and improving the power supply continuity to the backup load. When the control chip disconnects the relay, it outputs a low-level signal to the inverter through the hardware signal line. The transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the low-level signal, allowing the inverter to quickly switch to the voltage source control mode to supply power to the backup load, further improving the power supply continuity to the backup load during the grid connection and disconnection process. In addition, during the grid connection of the inverter, the inverter detects the grid voltage in the island operation mode. When it detects that the grid stops supplying power to the backup load and non-backup load, the wave is blocked, so that the control chip in the grid connection and disconnection controller can sense the power failure of the grid voltage, thereby smoothly realizing the grid connection and disconnection.

[0028] In some feasible implementations, the power supply system includes a photovoltaic system controller. Figure 2 , Figure 2 FIG. 1 is another schematic diagram of an application scenario of the power supply system provided by the present application. Figure 2As shown, the power supply system includes a photovoltaic system controller, which can communicate with the grid-connected and off-grid controller and the inverter through a serial port. For example, the grid-connected and off-grid controller and the inverter are connected to the photovoltaic system controller through an RS485 communication. The photovoltaic system controller is mainly responsible for communication transmission, power scheduling, information reporting and other functions in the power supply system.

[0029] In some feasible implementations, the inverter is used to send out an alarm signal and shut down after suspending the output of AC power for a period exceeding a first preset time interval. Figure 1 or Figure 2 In the power supply system shown, during the grid-connected operation of the inverter, the relays K1 and K2 in the grid-connected and off-grid controller are closed, and the inverter is in the current source control mode and supplies power to the backup load and the non-backup load. When the inverter enters the island operation mode, the inverter can detect the grid voltage. When the grid power failure is detected, the inverter is blocked and the output of AC power is suspended. If the inverter outputs AC power for more than a first preset time interval, for example, more than 20ms, an alarm signal is issued and the inverter is shut down. Here, the grid power failure is detected in the inverter island operation mode and the wave is blocked. If the grid-connected and off-grid controller has not sent a low-level signal to the inverter after the first preset time interval, the grid-connected and off-grid controller is abnormal. In order to enable the inverter to continue to supply power to the backup load in the environment of a grid failure, the inverter sends an alarm signal and shuts down for the next off-grid startup.

[0030] In some feasible implementations, the control chip in the on-grid and off-grid controller is used to control the relay to disconnect when the inverter is in the current source control mode, the relay is closed, and the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, and at the same time output a low-level signal to the inverter through the hardware signal line. Figure 1 or Figure 2 In the power supply system shown, the control chip is also used to detect the grid voltage amplitude during the inverter grid connection period. After detecting that the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, it is determined that the current grid voltage is powered off and the grid connection and disconnection conditions are met, then the control relays K1 and K2 are disconnected, and at the same time, a low-level signal is output to the inverter through the hardware signal line, so that the inverter switches from the current source control mode to the voltage source control mode. Here, the control chip controls the relay to disconnect after determining that the grid fails, and outputs a low-level signal or a high-level signal to the inverter through the hardware signal line, so that the inverter quickly switches to the voltage source control mode to supply power to the backup load, thereby improving the power supply continuity to the backup load during the grid connection and disconnection process.

[0031] In some feasible implementations, the disconnection speed of the first relay and the second relay included in the on-grid and off-grid controller is greater than the disconnection speed of the second relay. The control chip in the on-grid and off-grid controller is also used to detect that the instantaneous value of the grid voltage exceeds the set voltage range, or detects that the inverter stops outputting AC power, determines that the grid is faulty, and meets the conditions for on-grid disconnection. The control chip controls the first relay and the second relay to disconnect at the same time. Figure 2 Taking the power supply system shown in the figure as an example, the off-grid controller includes relays K1 and K2, and the disconnection speed of relay K1 is greater than that of relay K2. After the control chip determines that the grid is faulty, it controls relays K1 and K2 to disconnect at the same time. Here, since the disconnection speed of relay K1 is greater than that of relay K2, relay K1 can be disconnected faster, ensuring the quick disconnection of the inverter and the grid side.

[0032] In some feasible implementations, the power supply system includes multiple inverters, and the AC ends of the multiple inverters are connected in parallel and then connected to the inverter port of the grid-connected controller through a grid-connected point. Figure 3 , Figure 3 FIG. 1 is another schematic diagram of an application scenario of the power supply system provided by the present application. Figure 3 As shown, the power supply system includes multiple inverters, namely, inverter 1, inverter 2, ..., inverter n, where n is an integer greater than 1. The DC terminals of inverter 1, inverter 2, ..., inverter n are used to connect to a DC power source, and the AC terminals of multiple inverters are connected in parallel to the inverter port of the grid-connected controller through a grid-connected point. The above multiple inverters may include a DC conversion circuit and an inverter circuit. The specific connection relationship can be referred to the above Figure 1 The description will not be repeated here. Inverter 1, inverter 2, ..., inverter n are also connected to the grid-connected and off-grid controller through a hardware signal line, and are connected to the photovoltaic system controller through RS485 communication. When the inverter is in current source control mode, the relay is closed and the instantaneous value of the grid voltage is detected to exceed the set voltage range, or it is detected that the grid-connected point suspends the output of AC power, and the current grid fault is determined, the control chip controls relay K1 and relay K2 to disconnect, and outputs a low-level signal to the inverter through the hardware signal line. After receiving the low-level signal, the above-mentioned multiple inverters switch to the voltage source control mode, which improves the power supply continuity to the backup load during the grid-connected and off-grid process.

[0033] In some feasible implementations, if the inverter is a single-phase inverter, the above-mentioned on-grid and off-grid controller may be a single-phase on-grid and off-grid controller. Figure 4 , Figure 4 This is a hardware circuit diagram of the on-grid and off-grid controller provided by this application. Figure 4As shown, the on-grid and off-grid controller includes a first relay, namely relay K1, and the relay K1 may include a relay on the L line, or two relays on the L line and the N line. The on-grid and off-grid controller also includes a second relay, namely relay K2, and relay K2 includes two relays on the L line and the N line, and relay K1 and relay K2 are connected in series. In addition, the on-grid and off-grid controller also includes an NPE relay and a bypass switch, the NPE relay is connected on the N line, and the bypass switch is connected in parallel at both ends of the series relay K1 and relay K2. Here, when the above-mentioned relays K1 and K2 fail, causing the on-grid and off-grid controller to fail to operate normally, the bypass switch in the on-grid and off-grid controller can be manually closed to restore power to the backup load. The above-mentioned NPE relay is used to close when the inverter is off-grid, that is, when relays K1 and K2 are disconnected.

[0034] In some feasible implementations, if the inverter is a three-phase inverter, the above-mentioned on-grid and off-grid controller may be a three-phase on-grid and off-grid controller. Figure 5 , Figure 5 This is another hardware circuit diagram of the on-grid and off-grid controller provided by this application. Figure 5 As shown, the on-grid and off-grid controller includes a first relay, namely relay K1, and the relay K1 may include four relays on phase A, phase B, phase C and phase N. The on-grid and off-grid controller also includes a second relay, namely relay K2, and relay K2 may include four relays on phase A, phase B, phase C and phase N. Relay K1 and relay K2 are connected in series. In addition, the on-grid and off-grid controller also includes an NPE relay and a bypass switch, the NPE relay is connected to phase N, and the bypass switch is connected in parallel at both ends of the series-connected relay K1 and relay K2. Here, when the above-mentioned relays K1 and relay K2 fail, causing the on-grid and off-grid controller to fail to operate normally, the bypass switch in the on-grid and off-grid controller can be manually closed to restore power to the backup load. The above-mentioned NPE relay is used to close when the inverter is off-grid, that is, when relays K1 and relays K2 are disconnected.

[0035] See also Figure 6 , Figure 6 The power supply system grid connection and disconnection control method provided in this application is applicable to the above Figures 1 to 3 The grid-connection and grid-disconnection processes of the inverter in any power supply system shown.

[0036] like Figure 6 As shown, the power supply system grid connection and disconnection control method provided in the present application includes the following steps:

[0037] S601, detecting the grid side voltage.

[0038] S602, whether the power grid meets the grid connection and disconnection conditions, if the judgment result is yes, execute step S603, if the judgment result is no, execute step S601.

[0039] In some feasible implementations, during the inverter grid-connected operation, the relay is closed, the inverter is in current source control mode, and the inverter or the grid supplies power to the backup load and the non-backup load during the grid-connected period. When the inverter is grid-connected, when it is detected that the instantaneous value of the grid voltage exceeds the set voltage range, it is determined that the current grid is abnormal and the grid-connected disconnection conditions are met. Alternatively, when it is detected that the inverter suspends the output of AC power, it is determined that the current grid voltage is powered off and the grid-connected disconnection conditions are met.

[0040] In some feasible implementations, the grid voltage amplitude is detected during the inverter grid-connected period. After detecting that the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, it is determined that the current grid voltage has dropped and the grid connection and disconnection conditions are met.

[0041] S603, the control relay is disconnected, and at the same time a low level signal or a high level signal is output to the inverter through the hardware signal line.

[0042] In some feasible implementations, after determining that the current grid voltage meets the grid-connected and disconnected conditions, the control relay is disconnected, and at the same time, a low-level signal is output to the inverter through the hardware signal line, so that the inverter switches from the current source control mode to the voltage source control mode. Here, by detecting the instantaneous value of the grid voltage, the grid voltage abnormality can be detected before the inverter, avoiding the inverter from stopping working after detecting the grid fault first, thereby improving the power supply continuity to the backup load. When the relay is disconnected, a low-level signal is output to the inverter through the hardware signal line. The transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the low-level signal, so that the inverter quickly switches to the voltage source control mode to supply power to the backup load, further improving the power supply continuity to the backup load during the grid-connected and disconnected process. In addition, the inverter blocks the wave when it detects a power failure in the grid in the island operation mode, so that the grid voltage can be sensed to fail, and the grid-connected and disconnected switching can be smoothly realized.

[0043] The present application also provides an inverter, which includes an inverter circuit, a grid-connected relay and an off-grid relay. The DC end of the inverter is used to connect a DC power supply, the grid-connected port of the inverter is connected to the power grid, and the off-grid port of the inverter is used to connect a backup power load. The output end of the inverter circuit is connected to the grid-connected port through the grid-connected relay, and the output end of the inverter circuit is connected to the off-grid port through the off-grid relay. Figure 7 , Figure 7 is a schematic diagram of the application scenario of the inverter provided in this application. Figure 7As shown, the inverter may include a DC conversion circuit and an inverter circuit, the input end of the DC conversion circuit is used as the DC end of the inverter to be connected to the photovoltaic string, and the output end of the DC conversion circuit is connected to the input end of the inverter circuit. The inverter may also include a relay and a controller, for example, it may include a grid-connected relay and an off-grid relay (for the convenience of description, the grid-connected relay is referred to as relay K1, and the off-grid relay is referred to as relay K2), the output end of the inverter circuit is connected to the grid-connected port through relay K1, and the output end of the inverter circuit is connected to the off-grid port through relay K2. The above relay K1 and relay K2 may be a single relay or a relay group integrated with multiple relays. During the inverter grid-connected operation, at this time, relay K1 is closed, relay K2 is closed, the inverter is in the current source control mode, and the inverter or the power grid is used to jointly supply power to the backup load. The controller can determine that the grid is abnormal or power-off when the inverter is in the current source control mode, the relay K1 is closed, the relay K2 is closed, and the instantaneous value of the grid voltage is detected to exceed the set voltage range, or it is detected that the grid stops supplying power to the backup load, or after the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, and the grid disconnection conditions are met. At this time, the controller controls the relay K1 to disconnect, and at the same time switches the voltage source control mode to supply power to the backup load. Here, after detecting the abnormality of the grid or the power failure, the grid-connected relay is directly disconnected, and the voltage source mode is switched at the same time, thereby improving the continuity of power supply to the backup load.

Claims

1. A power supply system, characterized in that: The power supply system comprises an inverter and an on-grid and off-grid controller, wherein the DC end of the inverter is used to connect to a DC power source, and the AC end of the inverter is connected to an inverter port of the on-grid and off-grid controller; The on-grid and off-grid controller comprises a relay and a control chip, the backup power port of the on-grid and off-grid controller is used to connect the backup power load, and the grid port of the on-grid and off-grid controller is used to connect the grid, wherein the backup power port is connected to the inverter port, and the inverter port and the grid port of the on-grid and off-grid controller are connected via the relay; The inverter is used to convert the direct current from the direct current power supply into alternating current when it is in the current source control mode and the relay is closed, and the inverter or the power grid is used to jointly supply power to the backup load; The inverter is also used to stop outputting AC power after detecting that the power grid stops supplying power to the backup power load; The control chip is used to control the relay to disconnect when the inverter suspends outputting AC power, or when the instantaneous value of the grid voltage exceeds a set voltage range, and at the same time output a low-level signal or a high-level signal to the inverter through a hardware signal line, so that the inverter switches to a voltage source control mode and resumes outputting AC power to supply power to the backup load.

2. The power supply system according to claim 1, characterized in that: The inverter is used to send out an alarm signal and shut down after suspending output of alternating current for more than a first preset time interval.

3. The power supply system according to claim 1 or 2, characterized in that: The control chip is used to control the relay to disconnect after the grid voltage amplitude exceeds the set voltage range and exceeds the second preset time interval, and at the same time output the low level signal or the high level signal to the inverter through the hardware signal line.

4. The power supply system according to any one of claims 1 to 3, characterized in that: The relay comprises a first relay and a second relay connected in series, the first relay is connected to the inverter port, the second relay is connected to the grid port, and a disconnection speed of the first relay is greater than a disconnection speed of the second relay.

5. The power supply system according to any one of claims 1 to 4, characterized in that: The power supply system comprises a plurality of inverters, and the AC ends of the plurality of inverters are connected in parallel and connected to the inverter port of the grid-connected and off-grid controller through a grid-connected point; The control chip is used to control the relay to disconnect when the grid-connected point suspends outputting AC power, or when the instantaneous value of the grid voltage exceeds the set voltage range, and at the same time output a low-level signal or a high-level signal to the multiple inverters through the hardware signal line, so that the multiple inverters switch to a voltage source control mode and convert the DC power from the DC power supply into AC power to supply power to the backup power load.

6. The power supply system according to any one of claims 1 to 5, characterized in that: The non-backup power port of the on-grid and off-grid controller is used to connect a non-backup power load, and the non-backup power port is connected to the grid port; The inverter is also used for, in a current source control mode, the inverter or the power grid is used for jointly supplying power to the backup load and the non-backup load.

7. A method for controlling grid connection and disconnection of a power supply system, characterized in that: The method comprises: When the relay is closed and the inverter stops outputting AC power, or when the relay is closed and the instantaneous value of the grid voltage exceeds the set voltage range, the relay is controlled to be disconnected, and a low level signal or a high level signal is output to the inverter through a hardware signal line, so that the inverter switches to a voltage source control mode; The DC end of the inverter is used to connect to a DC power supply, and the AC end of the inverter is connected to a power grid via the relay.

8. The method according to claim 7, characterized in that The method further comprises: After the relay is closed and the grid voltage amplitude exceeds the set voltage interval and exceeds the second preset time interval, the relay is controlled to be disconnected, and a low level signal or a high level signal is output to the inverter through the hardware signal line.

9. An inverter, characterized in that: The inverter comprises an inverter circuit, a grid-connected relay and an off-grid relay, the DC end of the inverter is used to connect a DC power supply, the grid-connected port of the inverter is connected to the power grid, the off-grid port of the inverter is used to connect a backup power load, the output end of the inverter circuit is connected to the grid-connected port through the grid-connected relay, and the output end of the inverter circuit is connected to the off-grid port through the off-grid relay; The inverter is used to convert the direct current from the direct current power supply into alternating current when it is in the current source control mode and the off-grid relay is closed and the grid-connected relay is closed, and the inverter or the grid is used to jointly supply power to the backup load; The inverter is also used to control the grid-connected relay to disconnect and switch the voltage source control mode to convert the DC power from the DC power supply into AC power to power the backup power load when it is detected that the power grid stops supplying power to the backup power load, or when the instantaneous value of the power grid voltage exceeds the set voltage range, or when the power grid voltage amplitude exceeds the set voltage range and exceeds a second preset time interval.

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