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

Abstract

The embodiment of the invention provides a power supply system, a power supply system off-grid and grid-connected switching control method and an inverter. The power supply system comprises an inverter and a grid-connected and off-grid controller, the direct-current end of the inverter is connected with a direct-current power supply, and the alternating-current end of the inverter is connected with an inversion port of the grid-connected and off-grid controller. A standby power port and a power grid port of the grid-connected and off-grid controller are connected with a standby power load and a power grid respectively, 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 the inverter receives the power grid voltage information and adjusts the output voltage amplitude and the output voltage frequency according to the power grid voltage information. The control chip of the grid-connected and off-grid controller controls the relay to be closed when the difference between the inverter output voltage amplitude and the grid voltage amplitude, the difference between the inverter output voltage frequency and the grid voltage frequency, and the phase difference between the inverter output voltage phase and the grid voltage are all smaller than set threshold values. And outputting a high-level signal or a low-level signal to the inverter through a hardware signal line, so that the inverter switches a current source control mode.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to a power supply system, a power supply system off-grid and grid-connected control method, 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 the functions of grid-connected and off-grid, and parallel operation. The power supply system architecture is mainly divided into two types. One is a photovoltaic power storage integrated machine with independent grid-connected ports and off-grid ports; the other is a split photovoltaic power storage inverter and grid-connected and off-grid switching equipment to form a backup power system. However, for the switch from off-grid to grid-connected, the above two power supply systems have problems that need to be solved, such as the synchronization of the photovoltaic power storage inverter output voltage with the grid voltage, the continuity of load power supply during the grid-connected and off-grid switching process, and the grid connection meeting the grid standard requirements. Summary of the invention

[0003] The present application provides a power supply system, a power supply system off-grid and grid-connected control method and an inverter, which can avoid large current shocks caused by excessive difference between grid voltage and inverter port voltage and solve circulating current problems, while improving the power supply continuity to backup power loads during off-grid and grid-connected processes.

[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 supply power to the backup power load when it is in a voltage source control mode and the relay is disconnected. The inverter is also used to receive grid voltage information and adjust the output voltage amplitude and output voltage frequency according to the grid voltage information. The control chip is used to control the relay to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold value, and at the same time output a high-level signal or a low-level signal to the inverter through the hardware signal line, so that the inverter switches to the current source control mode, and the inverter or the grid is used to jointly supply power to the backup load.

[0005] In this embodiment, the control chip in the off-grid controller determines whether to switch from off-grid to on-grid based on the amplitude difference, frequency difference, and phase difference between the output voltage of the inverter and the grid voltage, thereby avoiding large current shocks caused by excessive difference between the grid voltage and the inverter port voltage, and solving the circulation problem of off-grid switching to on-grid switching when the inverter is paralleled, thereby improving equipment safety. In addition, when the relay is closed, a high-level signal or a low-level signal is output to the inverter through the hardware signal line, and the transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the high-level signal or the low-level signal, so that the inverter quickly switches to the current source control mode and supplies power to the backup load, improving the power supply continuity to the backup load during the off-grid switching process.

[0006] In one possible implementation, the control chip is used to send grid voltage information to the inverter when the relay is disconnected and the grid voltage amplitude reaches the set voltage range. After receiving the grid voltage information, the inverter switches to the virtual synchronous generator control mode and adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information. The on-grid controller determines whether to switch from off-grid to on-grid based on the amplitude difference, frequency difference and phase difference between the output voltage of the inverter and the grid voltage through the control chip, so as to avoid large current shock caused by excessive difference between the grid voltage and the inverter port voltage.

[0007] In a possible implementation, the control chip is used to send grid voltage information to the inverter after the relay is disconnected, the grid voltage amplitude reaches a set voltage range, and the grid voltage frequency reaches a set frequency range and maintains a set time interval. Here, by improving the accuracy of judging whether the grid connection conditions are met, grid connection under unstable grid conditions is avoided.

[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 maximum allowable impact current of the second relay is greater than the maximum allowable impact current of the first relay. Not all relays in the on-grid and off-grid controller are relays with large impact current resistance, saving equipment costs.

[0009] In a possible implementation, the control chip is further used to control the first relay to close after the inverter receives the grid voltage information. The control chip is also used to control the second relay to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold. The two relays are not closed at the same time, which can protect the relay with a smaller impact current resistance capability.

[0010] In a possible implementation, the power supply system includes multiple inverters, and the AC ends of the multiple inverters are connected in parallel and connected to the inverter port of the off-grid controller through the grid connection point. The control chip is also used to control the relay to close when the difference between the grid connection point voltage amplitude and the grid voltage amplitude, the difference between the grid connection point voltage frequency and the grid voltage frequency, and the difference between the grid connection point voltage phase and the grid voltage phase are all less than the set threshold, and at the same time output a high level signal or a low level signal to the inverter through the hardware signal line, so that the multiple inverters are switched to the current source control mode, and the multiple inverters or grids are used to jointly supply power to the backup load. By determining whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the grid connection point voltage and the grid voltage, a large current shock caused by the excessive difference between the grid voltage and the inverter port voltage is avoided, and the circulation problem of the inverter switching off-grid and on-grid is solved, thereby improving the safety of the equipment.

[0011] 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 to, after switching to the current source control mode, the inverter or the grid is used to jointly supply power to the backup power load and the non-backup power load.

[0012] In the second aspect, the present application provides a method for controlling off-grid and grid-connected power supply systems, the method comprising sending grid voltage information to the inverter when the relay is disconnected and the grid voltage amplitude reaches a set voltage range, so that the inverter adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information. When the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold, the relay is controlled to close, and a high-level signal or a low-level signal is output to the inverter through a hardware signal line, so that the inverter switches to a current source control mode. Among them, 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.

[0013] In this embodiment, by determining whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the inverter and the grid voltage, a large current shock caused by the large difference between the grid voltage and the inverter port voltage is avoided, and the circulation problem of switching from off-grid to grid-connected when the inverter is paralleled is solved, thereby improving the safety of the equipment. In addition, when the relay is closed, a high-level signal or a low-level signal is output to the inverter through the hardware signal line, and the transmission delay of the hardware signal line is within 1ms, which greatly improves the transmission speed of the grid-connected signal, so that the inverter can quickly switch to the current source control mode and supply power to the backup load, thereby improving the continuity of power supply to the backup load.

[0014] In a possible implementation, when the relay is disconnected and the grid voltage amplitude reaches the set voltage interval, the grid voltage information is sent to the inverter, including sending the grid voltage information to the inverter after the relay is disconnected, the grid voltage amplitude reaches the set voltage interval, and the grid voltage frequency reaches the set frequency interval and maintains the set time interval. Here, by improving the accuracy of judging whether the grid connection conditions are met, grid connection under unstable grid conditions is avoided.

[0015] In a possible implementation, the relay includes a first relay and a second relay connected in series, the maximum allowable inrush current of the second relay is greater than the maximum allowable inrush current of the first relay, and the method includes sending grid voltage information to the inverter when the first relay and the second relay are disconnected and the grid voltage amplitude reaches a set voltage range. Not all relays in the on-grid and off-grid controller use relays with large inrush current resistance, saving equipment costs.

[0016] In a possible implementation, the method includes controlling the first relay to close after the inverter receives the grid voltage information. When the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold, controlling the second relay to close. The two relays are not closed at the same time, so that the relay with a smaller impact current resistance capability can be protected.

[0017] 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 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 supply power to the backup power load when it is in a voltage source control mode and the off-grid relay is closed and the grid-connected relay is disconnected. The inverter is also used to adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information. The inverter is also used to control the grid-connected relay to close when the difference between the output voltage amplitude of the off-grid port and the grid voltage amplitude, the difference between the output voltage frequency of the off-grid port and the grid voltage frequency, and the difference between the output voltage phase of the off-grid port and the grid voltage phase are all less than a set threshold, and switch to the current source control mode at the same time, and the inverter or the grid is used to jointly supply power to the backup power load.

[0018] In this embodiment, by determining whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the off-grid port and the grid voltage, a large current shock caused by the large difference between the grid voltage and the output voltage of the off-grid port is avoided, and the circulation problem of switching from off-grid to grid-connected when the inverter is paralleled is solved, thereby improving the safety of the equipment. In addition, when the relay is closed, the inverter is controlled to switch to the current source control mode and supply power to the backup load, thereby improving the continuity of power supply to the backup load.

[0019] In a possible implementation, the inverter is further used to adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information when the grid voltage amplitude reaches the set voltage range when the off-grid relay is closed and the grid-connected relay is disconnected in the voltage source control mode. The inverter adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information, and determines whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the off-grid port and the grid voltage, thereby avoiding a large current shock caused by an excessively large difference between the grid voltage and the output voltage of the off-grid port.

[0020] In a possible implementation, the inverter is further used to adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information when the grid voltage amplitude reaches the set voltage interval and the grid voltage frequency reaches the set frequency interval and maintains the set time interval when the off-grid relay is closed and the grid-connected relay is disconnected in the voltage source control mode. Here, by improving the accuracy of judging whether the grid connection conditions are met, grid connection under unstable grid conditions is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of an application scenario of the power supply system provided by this application;

[0022] Figure 2 is a schematic diagram of another application scenario of the power supply system provided by the present application;

[0023] Figure 3 is a schematic diagram of another application scenario of the power supply system provided by the present application;

[0024] Figure 4 This is a hardware circuit diagram of an on-grid and off-grid controller provided by this application;

[0025] Figure 5 It is another hardware circuit diagram of the on-grid and off-grid controller provided by the present application;

[0026] Figure 6 It is a flow chart of the off-grid and grid-connected control method of the power supply system provided by the present application;

[0027] Figure 7 It is a schematic diagram of the application scenario of the inverter provided in this application. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] In some possible implementations, please refer again to Figure 1 The 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.

[0031] exist Figure 1In the application scenario shown, during the off-grid operation of the inverter, the on-grid and off-grid controller detects the grid voltage through the control chip. If the grid voltage meets the grid connection conditions, the inverter is controlled to switch from off-grid to grid-connected. In the currently used off-grid and grid-connected method, the large current impact caused by the large difference between the grid voltage and the inverter port voltage cannot be avoided during the closing process of the control relay, and the circulation problem of off-grid switching and grid-connected when the inverter is paralleled cannot be avoided, thereby causing damage to the device. In addition, in the process of controlling the inverter to switch from off-grid to grid-connected, the power supply continuity of important loads such as backup loads is not considered, and the power supply reliability of backup loads is poor.

[0032] In the power supply system provided by the present application, during the off-grid operation of the inverter, the relay in the off-grid controller is disconnected, the inverter is in voltage source control mode, and converts the DC power from the DC power supply into AC power to supply power to the backup load. Figure 1, the relay in the on-grid and off-grid controller may include two relays, for example, 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 the relay K2 is connected to the grid port. During the off-grid operation of the inverter, the relay K1 and the relay K2 in the on-grid and off-grid controller are disconnected, the inverter is in the voltage source control mode and only supplies power to the backup load. Then, the inverter can receive the grid voltage information, and adjust the output voltage amplitude and the output voltage frequency according to the grid voltage information, and the above grid voltage information can come from the control chip or other devices, and the grid voltage information can include the grid voltage amplitude, the grid voltage frequency and the grid voltage phase. The control chip in the grid-connected and off-grid controller is used to control relays K1 and K2 to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold, and at the same time, a high-level signal or a low-level signal is output to the inverter through the hardware signal line, so that the inverter switches from the voltage source control mode to the current source control mode. For example, taking a high-level signal as a grid-connected signal as an example, a high-level signal is output to the inverter through the hardware signal line to switch the inverter to the current source control mode. During the grid connection, the inverter or the grid supplies power to the backup load and the non-backup load. Here, the grid-connected and off-grid controller determines whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the inverter and the grid voltage through the control chip, thereby avoiding the generation of large current shocks due to the excessive difference between the grid voltage and the inverter port voltage, and at the same time solving the circulation problem of off-grid switching and grid-connected when the inverter is paralleled, thereby improving the safety of the equipment. In addition, when the relay is closed, a high-level signal or 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 high-level signal or the low-level signal, allowing the inverter to quickly switch to the current source control mode and supply power to the backup power load, improving the power supply continuity to the backup power load during the off-grid and grid-connected process.

[0033] 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 2 As shown, the power supply system includes a photovoltaic system controller, and the photovoltaic system controller 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 above-mentioned photovoltaic system controller is mainly responsible for communication transmission, power scheduling, information reporting and other functions in the power supply system. For example, the grid-connected and off-grid controller can send grid voltage information to the inverter through the photovoltaic system controller.

[0034] In some feasible implementations, the inverter can receive grid voltage information from the grid-connected and off-grid controller. Specifically, the grid-connected and off-grid controller detects the grid voltage through a control chip. When the inverter is in voltage source control mode, the relay is disconnected, and the grid voltage amplitude is detected to reach a set voltage range, the control chip determines that the current grid voltage meets the grid connection conditions, and sends the grid voltage information to the inverter, so that the inverter adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information. Figure 2 Taking the power supply system shown as an example, the grid-connected and off-grid controller detects the grid voltage through the control chip. When the inverter is in the voltage source control mode, the relay is disconnected, and the grid voltage amplitude is detected to reach the set voltage range, the control chip determines that the current grid voltage meets the grid connection conditions, and sends the grid voltage information to the photovoltaic system controller, so that the grid voltage information is sent to the inverter through the photovoltaic system controller. After receiving the above grid voltage information, the inverter switches to the virtual synchronous generator control mode and adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information. Then, the grid-connected and off-grid controller determines whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the inverter and the grid voltage through the control chip, thereby avoiding large current shocks caused by excessive difference between the grid voltage and the inverter port voltage.

[0035] In some feasible implementations, the on-grid and off-grid controller detects the grid voltage through a control chip. When the inverter is in voltage source control mode and the relay is disconnected, the control chip detects that the grid voltage amplitude reaches a set voltage range, the grid voltage frequency reaches a set frequency range and maintains a set time interval, and determines that the current grid voltage meets the grid connection conditions, and sends the grid voltage information to the inverter, so that the inverter adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information. Here, the accuracy of judging whether the grid connection conditions are met is improved, and grid connection under unstable grid conditions is avoided.

[0036] In some feasible implementations, the grid-connected and off-grid controller includes a first relay and a second relay, the maximum allowable impact current of the second relay is greater than the maximum allowable impact current of the first relay, and the control chip in the grid-connected and off-grid controller is also used to control the first relay to close after sending grid voltage information to the inverter or after the inverter receives grid voltage information, and control the second relay to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold. Figure 2Taking the power supply system shown as an example, the on-grid and off-grid controller includes relays K1 and K2, and the maximum allowable impact current of relay K2 is greater than the maximum allowable impact current of the above relay K1. After the control chip sends the grid voltage information to the inverter, or after the inverter receives the grid voltage information, the relay K1 is first controlled to close, and at the same time, when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold, the relay K2 is controlled to close. Here, the relays in the on-grid and off-grid controller are not all relays with large impact current resistance, which saves equipment costs, and the two relays are not closed at the same time, which can protect the relay with smaller impact current resistance.

[0037] 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 off-grid controller through a grid connection 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 of is not repeated here. Inverter 1, inverter 2, ..., inverter n are also connected to the grid-connected and off-grid controller through hardware signal lines, and are connected to the photovoltaic system controller through RS485 communication. When the inverter is in voltage source control mode, the relay is disconnected, and the grid voltage amplitude is detected to reach the set voltage range, the control chip determines that the current grid voltage meets the grid connection conditions, and sends the grid voltage information to the photovoltaic system controller, so that the grid voltage information is sent to multiple inverters through the photovoltaic system controller. After receiving the above-mentioned grid voltage information, multiple inverters switch to the virtual synchronous generator control mode and adjust the output voltage amplitude and output voltage frequency according to the grid voltage information. Next, when the difference between the voltage amplitude at the grid connection point and the voltage amplitude of the grid, the difference between the voltage frequency at the grid connection point and the voltage frequency of the grid, and the difference between the voltage phase at the grid connection point and the voltage phase of the grid are all less than the set threshold, the control chip controls relays K1 and K2 to close, and at the same time outputs high-level signals to inverter 1, inverter 2, ..., inverter n through the hardware signal line, so that multiple inverters switch to the current source control mode, and multiple inverters or grids are used to jointly supply power to the backup load, thereby avoiding large current shocks caused by excessive difference between the grid voltage and the inverter port voltage, and avoiding circulation problems between multiple inverters.

[0038] 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 4 As 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.

[0039] 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.

[0040] See also Figure 6 , Figure 6 The power supply system off-grid switching and grid-connection control method provided in this application is applicable to the above Figures 1 to 3 The off-grid switching and grid-connection process of the inverter in any power supply system shown in FIG. Figure 6As shown, the power supply system off-grid switching and grid-connection control method provided in the present application includes the steps of:

[0041] S601, detecting the grid-side voltage.

[0042] S602, whether the power grid meets the grid connection conditions, if the judgment result is yes, execute step S603, if the judgment result is no, execute step S601.

[0043] In some feasible implementations, during the off-grid operation of the inverter, the relay is disconnected, the inverter is in voltage source control mode and only supplies power to the backup load. When the inverter is off-grid, the grid voltage is detected. If the grid voltage amplitude is detected to reach the set voltage range, it is determined that the current grid voltage meets the grid connection conditions. Otherwise, the current grid voltage does not meet the grid connection conditions.

[0044] In some feasible implementations, by detecting the amplitude and frequency of the grid voltage, if it is detected that the grid voltage amplitude reaches the set voltage interval, the grid voltage frequency reaches the set frequency interval and maintains the set time interval, it is determined that the current grid voltage meets the grid connection conditions, otherwise, the current grid voltage does not meet the grid connection conditions. Here, the grid voltage amplitude, grid voltage frequency and time conditions are combined to improve the accuracy of the judgment on whether the grid connection conditions are met, and avoid grid connection under unstable grid conditions.

[0045] S603: Send grid voltage information to the inverter.

[0046] In some feasible implementations, after determining that the current grid voltage meets the grid connection conditions, the grid voltage information is sent to the inverter, so that the inverter adjusts the output voltage amplitude and the output voltage frequency according to the grid voltage information. After receiving the above-mentioned grid voltage information, the inverter switches to the virtual synchronous generator control mode and adjusts the output voltage amplitude and the output voltage frequency according to the grid voltage information. Here, the grid voltage information may include the grid voltage amplitude, the grid voltage frequency, and the grid voltage phase.

[0047] S604, detecting the voltage amplitude, phase and frequency on the grid side and the inverter side.

[0048] S605, whether the difference between the voltage amplitude, phase and frequency on the grid side and the inverter side is less than the set threshold, if the judgment result is yes, execute step S606, if the judgment result is no, execute step S604.

[0049] S606, controlling the relay to close, and outputting a high level signal or a low level signal to the inverter through the hardware signal line.

[0050] In some feasible implementations, after sending the grid voltage information to the inverter, the voltage amplitude, phase and frequency on the grid side and the inverter side are detected. When the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold, the control relay is closed, and a high level signal or a low level signal is output to the inverter through the hardware signal line, so that the inverter switches from the voltage source control mode to the current source control mode. For example, a high level signal is output to the inverter through the hardware signal line to switch the inverter to the current source control mode. During the grid connection, the inverter or the grid supplies power to the backup load and the non-backup load. Here, by determining whether to switch from off-grid to grid connection based on the amplitude difference, frequency difference and phase difference between the output voltage of the inverter and the grid voltage, a large current shock caused by the excessive difference between the grid voltage and the inverter port voltage is avoided, and the circulation problem of off-grid switching and grid connection when the inverter is paralleled is solved, thereby improving the safety of the equipment. In addition, when the relay is closed, a high-level signal or 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 grid-connected signal transmission speed, allowing the inverter to quickly switch to the current source control mode and supply power to the backup load, thereby improving the power supply continuity to the backup load.

[0051] 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 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-mentioned relay K1 and relay K2 may be a single relay or a relay group integrated with multiple relays. During the off-grid operation of the inverter, at this time, relay K1 is disconnected, relay K2 is closed, and the inverter is in voltage source control mode and only supplies power to the backup load. The controller can determine that the current grid voltage meets the grid connection condition when the inverter is in voltage source control mode, relay K1 is disconnected, relay K2 is closed, and the grid voltage amplitude is detected to reach the set voltage interval, or the grid voltage amplitude reaches the set voltage interval, the grid voltage frequency reaches the set frequency interval and maintains the set time interval. Then, the output voltage amplitude and output voltage frequency of the off-grid port are adjusted according to the grid voltage information. The above-mentioned grid voltage information can be obtained by the controller or from other devices, and the grid voltage information may include grid voltage amplitude, grid voltage frequency and grid voltage phase. When the difference between the output voltage amplitude of the off-grid port and the grid voltage amplitude, the difference between the output voltage frequency of the off-grid port and the grid voltage frequency, and the difference between the output voltage phase of the off-grid port and the grid voltage phase are all less than the set threshold, the controller controls relay K1 to close, and at the same time controls the inverter to switch to the current source control mode, and the inverter or the grid is used to jointly supply power to the backup load. Here, by determining whether to switch from off-grid to grid-connected based on the amplitude difference, frequency difference, and phase difference between the output voltage of the off-grid port and the grid voltage, a large current shock caused by the large difference between the grid voltage and the output voltage of the off-grid port is avoided, and the circulation problem of switching from off-grid to grid-connected when the inverter is paralleled is solved, thereby improving the safety of the equipment. In addition, when the relay is closed, the inverter is controlled to switch to the current source control mode and supply power to the backup load, 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 supply power to the backup load when it is in voltage source control mode and the relay is disconnected. The inverter is also used to receive grid voltage information and adjust the output voltage amplitude and output voltage frequency according to the grid voltage information; The control chip is used to control the relay to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold, and at the same time output a high-level signal or a low-level signal to the inverter through a hardware signal line, so that the inverter switches to a current source control mode, and the inverter or the grid is used to jointly power the backup power load.

2. The power supply system according to claim 1, characterized in that: The control chip is used to send the grid voltage information to the inverter when the relay is disconnected and the grid voltage amplitude reaches a set voltage range.

3. The power supply system according to claim 1, characterized in that: The control chip is used to send the grid voltage information to the inverter after the relay is disconnected, the grid voltage amplitude reaches a set voltage range, and the grid voltage frequency reaches a set frequency range and maintains a set time interval.

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 the maximum allowable impact current of the second relay is greater than the maximum allowable impact current of the first relay.

5. The power supply system according to claim 4, characterized in that: The control chip is also used to control the first relay to close after the inverter receives the grid voltage information; The control chip is also used to control the second relay to close when the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold.

6. The power supply system according to any one of claims 1 to 5, 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 also used to control the relay to close when the difference between the grid connection point voltage amplitude and the grid voltage amplitude, the difference between the grid connection point voltage frequency and the grid voltage frequency, and the difference between the grid connection point voltage phase and the grid voltage phase are all less than the set threshold value, and at the same time output a high level signal or a low level signal to the inverter through the hardware signal line, so that the multiple inverters switch to the current source control mode, and the multiple inverters or the grid are used to jointly power the backup power load.

7. The power supply system according to any one of claims 1 to 6, 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, after switching to the 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.

8. A method for controlling off-grid and on-grid connection of a power supply system, characterized in that: The method comprises: When the relay is disconnected and the grid voltage amplitude reaches the set voltage range, grid voltage information is sent to the inverter, so that the inverter adjusts the output voltage amplitude and output voltage frequency according to the grid voltage information; When the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than a set threshold, controlling the relay to close, and at the same time outputting a high level signal or a low level signal to the inverter through a hardware signal line, so that the inverter switches to a current 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.

9. The method according to claim 8, characterized in that When the relay is disconnected and the grid voltage amplitude reaches the set voltage range, the grid voltage information is sent to the inverter, including: After the relay is disconnected, the grid voltage amplitude reaches a set voltage interval, and the grid voltage frequency reaches a set frequency interval and maintains a set time interval, the grid voltage information is sent to the inverter.

10. The method according to claim 8, characterized in that The relay comprises a first relay and a second relay connected in series, the maximum allowable inrush current of the second relay is greater than the maximum allowable inrush current of the first relay, and the method comprises: When the first relay and the second relay are disconnected and the grid voltage amplitude reaches a set voltage range, the grid voltage information is sent to the inverter.

11. The method according to claim 10, characterized in that The method comprises: After the inverter receives the grid voltage information, controlling the first relay to close; When the difference between the output voltage amplitude of the inverter and the grid voltage amplitude, the difference between the output voltage frequency of the inverter and the grid voltage frequency, and the difference between the output voltage phase of the inverter and the grid voltage phase are all less than the set threshold, the second relay is controlled to close.

12. 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 supply power to the backup load when it is in voltage source control mode and the off-grid relay is closed and the grid-connected relay is disconnected; The inverter is also used to adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information; The inverter is also used to control the grid-connected relay to close and switch to the current source control mode when the difference between the output voltage amplitude of the off-grid port and the grid voltage amplitude, the difference between the output voltage frequency of the off-grid port and the grid voltage frequency, and the difference between the output voltage phase of the off-grid port and the grid voltage phase are all less than a set threshold value, and the inverter or the grid is used to jointly supply power to the backup power load.

13. The inverter according to claim 12, characterized in that: The inverter is also used to adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information when the grid voltage amplitude reaches a set voltage range when the inverter is in voltage source control mode, the off-grid relay is closed, and the grid-connected relay is disconnected.

14. The inverter according to claim 12, characterized in that: The inverter is also used to, when in voltage source control mode and the off-grid relay is closed and the grid-connected relay is disconnected, adjust the output voltage amplitude and output voltage frequency of the off-grid port according to the grid voltage information after the grid voltage amplitude reaches a set voltage interval and the grid voltage frequency reaches a set frequency interval and maintains a set time interval.

Images