Photovoltaic power generation system and control method thereof

Abstract

The embodiment of the invention discloses a photovoltaic power generation system and a control method thereof, and solves the problems of how to ensure the safety of the photovoltaic power generation system under the conditions of power failure of a power grid and off-grid starting of the photovoltaic power generation system, and how to ensure that an on-grid and off-grid switching device is simple in structure, low in cost and high in reliability. The controller is used for controlling the first switch to be switched on and controlling the second switch to be switched off when the power grid is powered off and the output voltage of the photovoltaic inverter is controlled to be smaller than or equal to a first voltage threshold value, and the first voltage threshold value is larger than zero and smaller than or equal to a human body safety voltage threshold value. The controller is further used for detecting the voltage difference value of the two ends of the second switch after controlling the first switch to be switched on, and switching off the photovoltaic inverter when the voltage difference value of the two ends of the second switch is larger than a second voltage threshold value and smaller than or equal to the voltage value of the output voltage of the photovoltaic inverter. And controlling the output voltage of the photovoltaic inverter to be increased to be greater than or equal to a third voltage threshold value, so that the photovoltaic inverter supplies power to the load.

Description

Technical Field

[0001] The present application relates to the field of energy technology, and in particular to a photovoltaic power generation system and a control method thereof. Background Art

[0002] The photovoltaic power generation system includes a photovoltaic inverter and an on-grid / off-grid switching device, which can also be called a whole-house backup box. The input end of the photovoltaic inverter is used to connect to the output end of the photovoltaic array, and the output end of the photovoltaic inverter is connected to the input end of the on-grid / off-grid switching device. The first output end of the on-grid / off-grid switching device is used to connect to the load, and the second output end of the on-grid / off-grid switching device is used to connect to the power grid.

[0003] Specifically, two switches connected in series are provided between the first output terminal and the second output terminal of the on-grid / off-grid switching device, and the two switches are respectively controlled by two driving circuits. Thus, when the grid is out of power and the photovoltaic power generation system is started off-grid, if any one of the two switches fails, the other switch can ensure that the on-grid / off-grid switching device is disconnected from the grid, so as to achieve isolation of the photovoltaic power generation system from the grid. Therefore, there is no safety and compliance risk, and the safety of the photovoltaic power generation system can be ensured.

[0004] However, the installation of two switches connected in series between the first and second output terminals of the on-grid / off-grid switching device, each controlled by two separate drive circuits, results in a complex, costly, and low-reliability on-grid / off-grid switching device. Therefore, in the event of a power outage and the off-grid startup of a photovoltaic power generation system, how can the on-grid / off-grid switching device be disconnected from the grid to isolate the photovoltaic power generation system from the grid, meet safety and compliance risk requirements, and ensure the safety of the photovoltaic power generation system? This has become an urgent problem to be solved, while also ensuring a simple, low-cost, and highly reliable on-grid / off-grid switching device. Summary of the Invention

[0005] The embodiment of the present application provides a photovoltaic power generation system and a control method thereof, which solves the problem of how to disconnect the on-grid and off-grid switching device from the power grid when the power grid is out and the photovoltaic power generation system is started off-grid, so as to achieve isolation of the photovoltaic power generation system from the power grid, meet safety and compliance risk requirements, ensure the safety of the photovoltaic power generation system, and at the same time, the on-grid and off-grid switching device has a simple structure, low cost and high reliability.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] In a first aspect of an embodiment of the present application, a photovoltaic power generation system is provided, comprising a photovoltaic inverter and an on-grid / off-grid switching device. The input of the photovoltaic inverter is connected to a photovoltaic array, and the output of the photovoltaic inverter is connected to the input of the on-grid / off-grid switching device. The photovoltaic inverter comprises a controller, and the on-grid / off-grid switching device comprises a first switch and a second switch. One end of the first switch is connected to the input of the on-grid / off-grid switching device, and the other end of the first switch is connected to one end of the second switch. The other end of the first switch is also connected to a load, and the other end of the second switch is connected to the power grid. The controller is configured to control the first switch to close and the second switch to open when the power grid is out and the output voltage of the photovoltaic inverter is less than or equal to a first voltage threshold. The first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold. The controller is further configured to detect a voltage difference across the second switch after controlling the first switch to close, and control the output voltage of the photovoltaic inverter to increase to a value greater than or equal to a third voltage threshold when the voltage difference across the second switch is greater than a second voltage threshold and less than or equal to a voltage value of the output voltage of the photovoltaic inverter, so that the photovoltaic inverter supplies power to the load, wherein the second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than a human safety voltage threshold.

[0008] Based on this solution, when the power grid is out and the output voltage of the photovoltaic inverter is controlled to be less than or equal to the first voltage threshold, the controller controls the first switch to close and the second switch to open. The AC power transmitted from the first switch to the second switch is used to detect adhesion faults on the second switch, thereby improving the accuracy of second switch fault detection. Secondly, because the output voltage of the photovoltaic inverter is less than or equal to the first voltage threshold, which is greater than zero and less than or equal to the human safety voltage threshold, in the event of a adhesion fault in the second switch, the voltage of the AC power output from the second switch to the grid will also be less than or equal to the human safety voltage threshold, which will not cause harm to grid maintenance personnel, meets safety and compliance risk requirements, and can ensure the safety of the photovoltaic power generation system. In addition, compared with the prior art in which, when the photovoltaic power generation system is started, the on-grid switching device disconnects from the grid by connecting two switches in series to achieve isolation of the photovoltaic power generation system from the grid, and the two switches are controlled by two drive circuits respectively, the on-grid switching device provided in the embodiment of the present application can disconnect from the grid by using the second switch, the one switch, to achieve isolation of the photovoltaic power generation system from the grid when the photovoltaic power generation system is started off-grid, without the need to control the second switch by two drive circuits. The on-grid switching device has a simple structure, low cost, and high reliability. Finally, when the voltage difference between the two ends of the second switch is greater than the second voltage threshold and less than or equal to the output voltage of the photovoltaic inverter, the controller determines that there is no adhesion fault in the second switch, and controls the output voltage of the photovoltaic inverter to increase to greater than or equal to the third voltage threshold so that the photovoltaic inverter supplies power to the load. The solution for detecting whether the second switch is stuck is simpler and can ensure that the photovoltaic inverter does not transmit a higher voltage to the grid through the second switch, thereby ensuring the safety of the photovoltaic power generation system.

[0009] In combination with the first aspect, in one possible implementation, the controller is further used to detect the voltage difference across the second switch after controlling the first switch to close, and control the first switch to open and control the photovoltaic inverter to shut down when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold. The fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

[0010] Based on this solution, when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold, the controller determines that the second switch has a sticking fault, controls the first switch to disconnect, and controls the photovoltaic inverter to shut down. The solution for detecting whether the second switch is stuck is simpler, and can ensure that the photovoltaic inverter does not transmit a higher voltage to the power grid through the second switch, thereby ensuring the safety of the photovoltaic power generation system.

[0011] In conjunction with the first aspect, in one possible implementation, the on-grid / off-grid switching device further includes a rectifier circuit and an energy storage device, wherein the input of the rectifier circuit is connected to the input of the on-grid / off-grid switching device, and the output of the rectifier circuit is connected to the input of the energy storage device, and the energy storage device is used to supply power to the on-grid / off-grid switching device. The controller is further configured to control the output voltage of the photovoltaic inverter to increase from zero to a value greater than or equal to a third voltage threshold before controlling the output voltage of the photovoltaic inverter to be less than or equal to the first voltage threshold, thereby charging the energy storage device. The controller is further configured to control the output voltage of the photovoltaic inverter to decrease to a value less than or equal to the first voltage threshold after controlling the output voltage of the photovoltaic inverter to be less than or equal to the first voltage threshold, if the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, after controlling the photovoltaic inverter to charge the energy storage device.

[0012] Based on this solution, the controller first controls the photovoltaic inverter to charge the energy storage device. When the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the energy storage device is fully charged, the controller then controls the output voltage of the photovoltaic inverter to be reduced to less than or equal to the first voltage threshold. The energy storage device is used to supply power to the on-grid and off-grid switching device, thereby preventing the on-grid and off-grid switching device from malfunctioning when the output voltage of the photovoltaic inverter is less than the third voltage threshold. This can improve the reliability of the on-grid and off-grid switching device and the reliability of the photovoltaic power generation system.

[0013] In combination with the first aspect, in one possible implementation, the energy storage device is used to supply power to the on-grid and off-grid switching device from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment being the moment when the output voltage of the photovoltaic inverter increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

[0014] Based on this solution, the energy storage device is used to supply power to the grid-connected and off-grid switching device from a first moment to a second moment. The first moment is when the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold. The second moment is when the output voltage of the photovoltaic inverter increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold. This can avoid the grid-connected and off-grid switching device from failing to operate normally when the output voltage of the photovoltaic inverter is less than the third voltage threshold, thereby improving the reliability of the grid-connected and off-grid switching device and the reliability of the photovoltaic power generation system.

[0015] In combination with the first aspect, in a possible implementation, the energy storage device includes a capacitor or a lithium battery.

[0016] According to a second aspect of an embodiment of the present application, a control method for a photovoltaic power generation system is provided. The method is applied to a photovoltaic power generation system, and includes: a controller controlling a first switch to close and a second switch to open when a power grid outage occurs and the output voltage of a photovoltaic inverter is controlled to be less than or equal to a first voltage threshold, wherein the first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold. After controlling the first switch to close, the controller detects a voltage difference across the second switch. When the voltage difference across the second switch is greater than the second voltage threshold and less than or equal to the output voltage of the photovoltaic inverter, the controller controls the output voltage of the photovoltaic inverter to increase to a value greater than or equal to a third voltage threshold, so that the photovoltaic inverter supplies power to a load. The second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold. The photovoltaic power generation system includes a photovoltaic inverter and an on-grid switching device. The input of the photovoltaic inverter is connected to a photovoltaic array, and the output of the photovoltaic inverter is connected to the input of the on-grid switching device. The photovoltaic inverter includes a controller, and the on-grid and off-grid switching device includes a first switch and a second switch. One end of the first switch is connected to the input end of the on-grid and off-grid switching device, and the other end of the first switch is connected to one end of the second switch. The other end of the first switch is also used to connect to the load, and the other end of the second switch is used to connect to the power grid.

[0017] In combination with the second aspect, in a possible implementation, the method further includes: after controlling the first switch to close, the controller detects the voltage difference across the second switch, and when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold, controls the first switch to open and controls the photovoltaic inverter to shut down, and the fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

[0018] In conjunction with the second aspect, in one possible implementation, the method further includes: before controlling the output voltage of the photovoltaic inverter to be less than or equal to the first voltage threshold, the controller controls the output voltage of the photovoltaic inverter to increase from zero to greater than or equal to a third voltage threshold to charge the energy storage device. After controlling the photovoltaic inverter to charge the energy storage device, the controller controls the output voltage of the photovoltaic inverter to decrease to less than or equal to the first voltage threshold when the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold. The on-grid switching device further includes a rectifier circuit and an energy storage device, wherein the input end of the rectifier circuit is connected to the input end of the on-grid switching device, and the output end of the rectifier circuit is connected to the input end of the energy storage device, and the energy storage device is used to supply power to the on-grid switching device.

[0019] In combination with the second aspect, in one possible implementation, the energy storage device is used to supply power to the on-grid and off-grid switching device from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment being the moment when the output voltage of the photovoltaic inverter increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

[0020] In conjunction with the second aspect, in a possible implementation, the energy storage device includes a capacitor or a lithium battery.

[0021] According to a third aspect of the embodiments of the present application, a photovoltaic inverter is provided, comprising a controller, an inverter circuit, a first switch, and a second switch. The input end of the inverter circuit is connected to a photovoltaic array, the output end of the inverter circuit is connected to one end of the first switch, and the other end of the first switch is connected to one end of the second switch. The other end of the first switch is also connected to a load, and the other end of the second switch is connected to the power grid. The controller is configured to control the first switch to close and the second switch to open when a power grid power outage occurs and the output voltage of the inverter circuit is controlled to be less than or equal to a first voltage threshold. The first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold. The controller is further configured to detect a voltage difference across the second switch after controlling the first switch to close. If the voltage difference across the second switch is greater than the second voltage threshold and less than or equal to the output voltage of the inverter circuit, the controller controls the output voltage of the inverter circuit to increase to a third voltage threshold, thereby enabling the photovoltaic inverter to supply power to the load. The second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold.

[0022] In combination with the third aspect, in one possible implementation, the controller is further used to detect the voltage difference across the second switch after controlling the first switch to close, and control the first switch to open and control the photovoltaic inverter to shut down when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold. The fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

[0023] In conjunction with the third aspect, in one possible implementation, the photovoltaic inverter further includes a rectifier circuit and an energy storage device, wherein the input of the rectifier circuit is connected to the output of the inverter circuit, and the output of the rectifier circuit is connected to the input of the energy storage device, and the energy storage device is used to supply power to the photovoltaic inverter. The controller is further configured to control the output voltage of the inverter circuit to increase from zero to a value greater than or equal to a third voltage threshold before controlling the output voltage of the inverter circuit to be less than or equal to the first voltage threshold, thereby charging the energy storage device. The controller is further configured to control the output voltage of the inverter circuit to decrease to a value less than or equal to the first voltage threshold after controlling the output voltage of the inverter circuit to charge the energy storage device, if the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold.

[0024] In combination with the third aspect, in one possible implementation, the energy storage device is used to supply power to the photovoltaic inverter from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment being the moment when the output voltage of the inverter circuit increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

[0025] In conjunction with the third aspect, in one possible implementation, the energy storage device includes a capacitor or a lithium battery.

[0026] The description of the second and third aspects in this application can refer to the detailed description of the first aspect; and the beneficial effects of the second and third aspects can refer to the analysis of the beneficial effects of the first aspect, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of a circuit topology of a photovoltaic power generation system;

[0028] Figure 2 A schematic diagram of a circuit topology of a photovoltaic power generation system provided in an embodiment of the present application;

[0029] Figure 3 A schematic diagram of a curve showing the output voltage of a photovoltaic inverter provided in an embodiment of the present application;

[0030] Figure 4 A schematic diagram of a circuit topology of another photovoltaic power generation system provided in an embodiment of the present application;

[0031] Figure 5 A schematic flow chart of a control method for a photovoltaic power generation system provided in an embodiment of the present application;

[0032] Figure 6 A flow chart of another control method for a photovoltaic power generation system provided in an embodiment of the present application;

[0033] Figure 7 A schematic diagram of a circuit topology of a photovoltaic inverter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following sections discuss the making and use of various embodiments in detail. However, it should be understood that many applicable inventive concepts provided herein can be implemented in a variety of specific contexts. The specific embodiments discussed are intended merely to illustrate specific ways to implement and use the present description and technology and are not intended to limit the scope of this application.

[0035] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0036] Various circuits or other components may be described or referred to as being "configured to" perform one or more tasks. In this case, "configured to" is used to imply structure by indicating that the circuit / component includes structure (e.g., circuitry) that performs the one or more tasks during operation. Thus, even when a specified circuit / component is not currently operational (e.g., not turned on), the circuit / component may be referred to as being configured to perform the task. Circuits / components used with the phrase "configured to" include hardware, such as circuitry that performs an operation, etc.

[0037] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. In the present application, "at least one" refers to one or more, and "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c or a, b and c, where a, b and c can be single or multiple. In addition, in the embodiments of the present application, words such as "first" and "second" do not limit the quantity and order.

[0038] In this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0039] Before introducing the embodiments of the present application, the technical terms and background technologies involved in the present application are first introduced.

[0040] Photovoltaic array: A photovoltaic array includes at least one photovoltaic component. When a photovoltaic array includes multiple photovoltaic components, the multiple photovoltaic components can be connected in series, or connected in parallel, or some of the multiple photovoltaic components can be connected in series and the remaining photovoltaic components can be connected in parallel.

[0041] like Figure 1 FIG. 1 is a schematic diagram of a circuit topology of a photovoltaic power generation system 100. The photovoltaic power generation system 100 includes a photovoltaic inverter 110 and an on-grid / off-grid switching device 120. The input of the photovoltaic inverter 110 is connected to the output of the photovoltaic array 200. The output of the photovoltaic inverter 110 is connected to the input of the on-grid / off-grid switching device 120. The first output of the on-grid / off-grid switching device 120 is connected to a load 300. The second output of the on-grid / off-grid switching device 120 is connected to a power grid 400. The first output of the on-grid / off-grid switching device 120 can be referred to as an off-grid port, and the second output of the on-grid / off-grid switching device 120 can be referred to as a on-grid port.

[0042] Specifically, refer to Figure 1 The on-grid / off-grid switching device 120 includes a first switch K1, a second switch K2, and a third switch K3. One end of the first switch K1 is connected to the input end of the on-grid / off-grid switching device 120, the other end of the first switch K1 is connected to the first output end of the on-grid / off-grid switching device 120 and one end of the second switch K2, the other end of the second switch K2 is connected to one end of the third switch K3, and the other end of the third switch K3 is connected to the second output end of the on-grid / off-grid switching device 120.

[0043] The photovoltaic array 200 is used to convert solar energy into direct current, the photovoltaic inverter 110 is used to convert the direct current into alternating current, and the on-grid and off-grid switching device 120 is used for on-grid and off-grid switching. Figure 1 When the photovoltaic power generation system 100 is connected to the grid, the first switch K1, the second switch K2 and the third switch K3 in the on-grid and off-grid switching device 120 are all closed, and the on-grid and off-grid switching device 120 is used to transmit AC power to the grid 400, or receive AC power from the grid 400. Figure 1The photovoltaic power generation system 100 also includes an energy storage device 130 connected to the photovoltaic inverter 110. When the power grid 400 is out of power and the photovoltaic inverter 110 is in a shutdown state, for example, due to the lack of sunlight at night and the low power of the energy storage device 130 being insufficient to supply power to the load 300, the photovoltaic inverter 110 is in a shutdown state. In this case, the photovoltaic power generation system 100 needs to be started off-grid. Specifically, the photovoltaic array 200 is used to convert solar energy into direct current during the day, and the photovoltaic inverter 110 is used to receive the direct current and start self-testing. After the self-test is completed, the photovoltaic inverter 110 starts to work and converts the direct current into alternating current, and the first switch K1 in the grid-off switching device 120 is closed, and the second switch K2 and the third switch K3 are both in the open state, thereby transmitting the alternating current to the load 300 and disconnecting the grid-off switching device 120 from the grid 400 to achieve isolation of the photovoltaic power generation system 100 from the grid 400.

[0044] In the on-grid / off-grid switching device 120, a second switch K2 and a third switch K3 are provided, and the two switches are controlled separately by two drive circuits. Thus, when the photovoltaic power generation system 100 is started off-grid and either the second switch K2 or the third switch K3 fails, the other switch can ensure that the on-grid / off-grid switching device 120 is disconnected from the grid 400, thereby isolating the photovoltaic power generation system 100 from the grid 400. Therefore, there is no safety and compliance risk, and the safety of the photovoltaic power generation system 100 can be ensured. For example, when a power grid failure causes a power outage and personnel maintenance is required, the photovoltaic power generation system 100 is started off-grid. If there is a adhesion fault in either the second switch K2 or the third switch K3, the other switch can ensure that the on-grid and off-grid switching device 120 is disconnected from the grid 400 to achieve isolation of the photovoltaic power generation system 100 from the grid 400, thereby preventing the on-grid and off-grid switching device 120 from transmitting AC power to the grid 400, and preventing the AC power from causing harm to grid maintenance personnel. Therefore, there is no safety and compliance risk, and the reliability of the photovoltaic power generation system 100 can be ensured.

[0045] However, a second switch K2 and a third switch K3 connected in series are provided between the first output terminal and the second output terminal of the on-grid / off-grid switching device 120, and these two switches are controlled separately by two drive circuits. This results in a complex structure, high cost, and low reliability for the on-grid / off-grid switching device 120. Furthermore, these two switches require fault detection under various operating conditions, and the solution for performing fault detection on these two switches is complex and difficult to implement. Therefore, in the event of a power outage and the photovoltaic power generation system 100 being started off-grid, how can the on-grid / off-grid switching device 120 be disconnected from the power grid 400 to meet safety and compliance risk requirements and ensure the safety of the photovoltaic power generation system 100? At the same time, how can the on-grid / off-grid switching device 120 be simple in structure, low in cost, and highly reliable, and how can the fault detection solution be simple and easy to implement? This is an urgent problem that needs to be solved.

[0046] Based on this, an embodiment of the present application provides a photovoltaic power generation system. When the power grid is out and the photovoltaic power generation system is started off-grid, the on-grid and off-grid switching device is disconnected from the power grid through a switch to achieve isolation of the photovoltaic power generation system from the power grid. Therefore, the on-grid and off-grid switching device has a simple structure, low cost, and high reliability, and the solution for detecting whether the switch is stuck is simple. When the switch is stuck, the voltage of the AC power output by the on-grid and off-grid switching device to the power grid is less than or equal to the human safety voltage, and will not cause harm to power grid maintenance personnel. It meets the safety and compliance risk requirements and can ensure the safety of the photovoltaic power generation system.

[0047] like Figure 2 The figure shows a circuit topology diagram of a photovoltaic power generation system 500 provided in an embodiment of the present application. The photovoltaic power generation system 500 includes a photovoltaic inverter 510 and an on-grid / off-grid switching device 520. The input end of the photovoltaic inverter 510 is used to connect to the photovoltaic array 200, and the output end of the photovoltaic inverter 510 is connected to the input end of the on-grid / off-grid switching device 520. The photovoltaic inverter 510 includes a controller 511. The on-grid / off-grid switching device 520 includes a first switch K1 and a second switch K2. One end of the first switch K1 is connected to the input end of the on-grid / off-grid switching device 520, and the other end of the first switch K1 is connected to one end of the second switch K2. The other end of the first switch K1 is also used to connect to the load 300. The other end of the first switch K1 can be referred to as the off-grid port. The other end of the second switch K2 is used to connect to the power grid 400. The other end of the second switch K2 can be referred to as the on-grid port.

[0048] The photovoltaic array 200 is used to convert solar energy into direct current, the photovoltaic inverter 510 is used to convert the direct current into alternating current, and the on-grid and off-grid switching device 520 is used for on-grid and off-grid switching. Figure 2When the photovoltaic power generation system 500 is connected to the grid, the first switch K1 and the second switch K2 in the on-grid and off-grid switching device 520 are both closed, and the on-grid and off-grid switching device 520 is used to transmit AC power to the grid 400, or receive AC power from the grid 400.

[0049] When the grid 400 is out of power, the photovoltaic inverter 510 is in a shutdown state, for example, referring to Figure 2 The photovoltaic power generation system 500 may further include an energy storage device 530 connected to the photovoltaic inverter 510. Since there is no sunlight at night and the power of the energy storage device 530 is insufficient to supply power to the load 300, the photovoltaic inverter 510 is in a shutdown state. When the photovoltaic power generation system 500 is started off-grid:

[0050] The photovoltaic array 200 is used to convert solar energy into direct current (DC) during the day. The photovoltaic inverter 510 receives this DC power and begins self-testing. After the self-test is complete, the photovoltaic inverter 510 begins operating to convert the DC power into alternating current (AC) and supplies power to the load 300 via the on-grid / off-grid switching device 520. Specifically, in the event of a power outage on the grid 400, typically due to a fault on the grid 400, requiring grid maintenance personnel to perform maintenance on the grid 400, the controller 511 controls the first switch K1 to close and the second switch K2 to open, thereby disconnecting the on-grid / off-grid switching device 520 from the grid 400. This prevents the AC power output by the photovoltaic inverter 510 from being transmitted to the grid 400 via the second switch K2, thus preventing harm to grid maintenance personnel. This isolates the photovoltaic inverter 510 from the grid 400, complies with safety and compliance risk requirements, and ensures the safety of the photovoltaic power generation system 500.

[0051] When the second switch K2 is functioning normally, the controller 511 can control the second switch K2 in the on-grid / off-grid switching device 520 to close or open. However, if a sticking fault occurs in the second switch K2, the second switch K2 will remain closed, and the controller 511 will be unable to control the second switch K2 to open. Therefore, to ensure the safety of the photovoltaic power generation system 500, when the grid 400 is out of power and the photovoltaic inverter 510 supplies power to the load 300 via the on-grid / off-grid switching device 520, the controller 511 controls the first switch K1 to close. Before controlling the second switch K2 to open, the controller 511 needs to determine whether a sticking fault has occurred in the second switch K2.

[0052] Specifically, the controller 511 is used to control the output voltage of the photovoltaic inverter 510 when the power grid is outage. Figure 3As shown in the ab section, when the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold, the first switch K1 is controlled to be closed and the second switch K2 is controlled to be disconnected. The first voltage threshold is greater than zero and less than or equal to the human safety voltage threshold. The embodiment of the present application does not limit the specific value of the first voltage threshold. When there is no source at both ends of the second switch K2, the accuracy of the second switch K2 fault detection is low. When the output voltage of the photovoltaic inverter 510 is controlled to be less than or equal to the first voltage threshold, the controller 511 controls the first switch K1 to be closed and the second switch K2 to be disconnected. The AC power transmitted from the first switch K1 to the second switch K2 is used to detect the adhesion fault of the second switch K2. The controller 511 can determine whether the second switch K2 has a adhesion fault by detecting the voltage difference between the two ends of the second switch K2 and comparing the voltage difference between the two ends of the second switch K2 with the voltage value of the output voltage of the photovoltaic inverter 510, thereby improving the accuracy of the second switch K2 fault detection. For example, if the controller 511 detects that the voltage difference across the second switch K2 is close to or equal to the output voltage of the photovoltaic inverter 510, it can determine that the second switch K2 has not experienced a sticking fault. Alternatively, if the controller 511 detects that the voltage difference across the second switch K2 is close to or equal to zero, it can determine that the second switch K2 has experienced a sticking fault. Furthermore, because the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold, if the second switch K2 has a sticking fault, the voltage of the AC power output by the second switch K2 to the power grid 400 will also be less than or equal to the human safety voltage threshold, thus preventing harm to power grid maintenance personnel. This meets safety and compliance risk requirements and ensures the safety of the photovoltaic power generation system 500.

[0053] The controller 511 is further configured to detect a voltage difference across the second switch K2 after controlling the first switch K1 to close, and to control the output voltage of the photovoltaic inverter 510 to be as follows: Figure 3As shown in the bc section of FIG, the output voltage of the photovoltaic inverter 510 increases to a value greater than or equal to the third voltage threshold, so that the photovoltaic inverter 510 supplies power to the load 300. The second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold. The embodiment of the present application does not limit the specific values ​​of the second and third voltage thresholds. Thus, compared with the above-mentioned photovoltaic power generation system 100 startup, the on-grid switching device 120 disconnects from the grid 400 by using two switches connected in series to isolate the photovoltaic power generation system 100 from the grid 400, and the two switches are controlled by two drive circuits respectively. When the photovoltaic power generation system 500 is started off-grid, the on-grid switching device 520 can disconnect from the grid 400 by using the second switch K2, a single switch, to isolate the photovoltaic power generation system 500 from the grid 400. There is no need to control the second switch K2 by two drive circuits. The on-grid switching device 520 has a simple structure, low cost, and high reliability. Secondly, when the voltage difference between the two ends of the second switch K2 is greater than the second voltage threshold and less than or equal to the voltage value of the output voltage of the photovoltaic inverter 510, the controller 511 determines that there is no adhesion fault in the second switch K2, and controls the photovoltaic inverter 510 to supply power to the load 300. The solution for detecting whether the second switch K2 is adhered is simpler and can ensure that the photovoltaic inverter 510 does not transmit a higher voltage to the power grid 400 through the second switch K2, thereby ensuring the safety of the photovoltaic power generation system 500.

[0054] In one possible embodiment, the controller 511 is further configured to, after controlling the first switch K1 to close, detect a voltage difference across the second switch K2. If the voltage difference across the second switch K2 is greater than or equal to zero and less than or equal to a fourth voltage threshold, and it is determined that the second switch K2 has a sticking fault, the controller 511 controls the first switch K1 to open and controls the photovoltaic inverter 510 to shut down. The fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold. The embodiment of the present application does not limit the specific value of the fourth voltage threshold. If the voltage difference across the second switch K2 is greater than or equal to zero and less than or equal to the fourth voltage threshold, and it is determined that the second switch K2 has a sticking fault, the controller 511 controls the first switch K1 to open and controls the photovoltaic inverter 510 to shut down. This solution for detecting whether the second switch K2 is stuck is simpler and can ensure that the photovoltaic inverter 510 does not transmit a higher voltage to the power grid 400 through the second switch K2, thereby ensuring the safety of the photovoltaic power generation system 500.

[0055] In a possible embodiment, the first switch K1 or the second switch K2 may be a relay or a contactor, which is not limited in this embodiment of the present application.

[0056] In a possible embodiment, the controller 511 includes a digital signal processing (DSP) chip or a microcontroller unit (MCU), which may also be called a single chip microcomputer, and is not limited in the embodiment of the present application.

[0057] In a possible embodiment, the controller 511 may be provided outside the photovoltaic inverter 510 , and the controller 511 may be an independent device in the photovoltaic power generation system 500 .

[0058] In the photovoltaic power generation system 500 provided in the embodiment of the present application, the controller 511 controls the first switch K1 to be closed and the second switch K2 to be opened when the power grid 400 is out and the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold. The AC power transmitted from the first switch K1 to the second switch K2 is used to detect adhesion faults on the second switch K2, thereby improving the accuracy of fault detection on the second switch K2. Secondly, since the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold, which is greater than zero and less than or equal to the human safety voltage threshold, in the event of an adhesion fault in the second switch K2, the voltage of the AC power output by the second switch K2 to the grid 400 will also be less than or equal to the human safety voltage threshold, which will not cause harm to grid maintenance personnel, meets safety compliance risk requirements, and can ensure the safety of the photovoltaic power generation system 500. In addition, compared with the above-mentioned photovoltaic power generation system 100 when it is started, the on-grid and off-grid switching device 120 is disconnected from the power grid 400 by two switches connected in series to achieve isolation of the photovoltaic power generation system 100 from the power grid 400, and the two switches are respectively controlled by two driving circuits. When the photovoltaic power generation system 500 is started off-grid, the on-grid and off-grid switching device 520 can be disconnected from the power grid 400 by a second switch K2, that is, a single switch, to achieve isolation of the photovoltaic power generation system 500 from the power grid 400. There is no need to control the second switch K2 through two driving circuits. The on-grid and off-grid switching device 520 has a simple structure, low cost, and high reliability. Finally, when the voltage difference between the two ends of the second switch K2 is greater than the second voltage threshold and less than or equal to the voltage value of the output voltage of the photovoltaic inverter 510, the controller 511 determines that there is no adhesion fault in the second switch K2. Then, the controller controls the output voltage of the photovoltaic inverter 510 to increase to greater than or equal to the third voltage threshold, so that the photovoltaic inverter 510 supplies power to the load 300. The solution for detecting whether the second switch K2 is stuck is simpler and can ensure that the photovoltaic inverter 510 does not transmit a higher voltage to the power grid 400 through the second switch K2, thereby ensuring the safety of the photovoltaic power generation system 500.

[0059] In one possible embodiment, Figure 4As shown, in the photovoltaic power generation system 500 provided in the embodiment of the present application, the grid-connected and off-grid switching device 520 further includes a rectifier circuit 521 and an energy storage device 522. The input end of the rectifier circuit 521 is connected to the input end of the grid-connected and off-grid switching device 520, and the output end of the rectifier circuit 521 is connected to the input end of the energy storage device 522. The energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520. For example, referring to Figure 4 The on-grid and off-grid switching device 520 may further include a detection controller 523 connected to the energy storage device 522. The energy storage device 522 may be used to supply power to the detection controller 523. The detection controller 523 is used to communicate with the controller 511. The detection controller 523 is also used to control the first switch K1 and the second switch K2 in the on-grid and off-grid switching device 520 and detect the voltage difference across the second switch K2.

[0060] In a possible embodiment, the energy storage device 522 includes a capacitor or a lithium battery, which is not limited in this embodiment of the present application.

[0061] The controller 511 is also used to control the output voltage of the photovoltaic inverter 510. Figure 3 As shown in the ab section in FIG, before the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold, the output voltage of the photovoltaic inverter 510 is controlled as follows Figure 3 As shown in the de section of FIG, the output voltage of the photovoltaic inverter 510 increases from zero to a value greater than or equal to the third voltage threshold to charge the energy storage device 522. The controller 511 is further configured to control the output voltage of the photovoltaic inverter 510 to be as follows: Figure 3 As shown in the segment fa in FIG, the output voltage of the photovoltaic inverter 510 decreases to less than or equal to the first voltage threshold. The embodiment of the present application does not limit the specific values ​​of the fifth voltage threshold and the voltage fluctuation threshold.

[0062] In a possible embodiment, the energy storage device 522 is used to supply power to the grid-connected / off-grid switching device 520 from a first moment to a second moment, wherein the first moment is when the voltage of the energy storage device 522 is greater than or equal to a fifth voltage threshold, and the voltage fluctuation of the energy storage device 522 is less than or equal to the voltage fluctuation threshold, and the energy storage device 522 is fully charged, for example Figure 3 The second moment is the moment when the output voltage of the photovoltaic inverter 510 increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold, for example Figure 3At moment c in the figure, it can be understood that the energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520 in the time period between moment f and moment c, thereby avoiding the situation where the output voltage of the photovoltaic inverter 510 is less than the third voltage threshold and the grid-connected and off-grid switching device 520 cannot work normally, which can improve the reliability of the grid-connected and off-grid switching device 520 and the reliability of the photovoltaic power generation system 500.

[0063] In a possible embodiment, the controller 511 may be provided in the on-grid and off-grid switching device 520 and integrated with the detection controller 523 .

[0064] In a possible embodiment, the on-grid and off-grid switching device 520 may be provided in the photovoltaic inverter 510 , and the on-grid and off-grid switching device 520 and the photovoltaic inverter 510 may be sold as a photovoltaic inverter.

[0065] In the photovoltaic power generation system 500 provided in the embodiment of the present application, the grid-connected and off-grid switching device 520 further includes an energy storage device 522. The controller 511 first controls the photovoltaic inverter 510 to charge the energy storage device 522. When the voltage of the energy storage device 522 is greater than or equal to the fifth voltage threshold, and the voltage fluctuation of the energy storage device 522 is less than or equal to the voltage fluctuation threshold, and the energy storage device 522 is fully charged, the output voltage of the photovoltaic inverter 510 is controlled to be reduced to less than or equal to the first voltage threshold. The energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520, thereby preventing the grid-connected and off-grid switching device 520 from malfunctioning when the output voltage of the photovoltaic inverter 510 is less than the third voltage threshold. This can improve the reliability of the grid-connected and off-grid switching device 520 and the reliability of the photovoltaic power generation system 500.

[0066] like Figure 5 As shown, an embodiment of the present application further provides a control method for a photovoltaic power generation system, which is applied to the above-mentioned photovoltaic power generation system 500. The method includes steps S501 and S502.

[0067] S501, when the power grid 400 is out of power and the output voltage of the photovoltaic inverter 510 is controlled to be less than or equal to a first voltage threshold, the controller 511 controls the first switch K1 to be closed and the second switch K2 to be open, and the first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold.

[0068] In a possible embodiment, when the controller 511 controls the output voltage of the photovoltaic inverter 510 to be greater than the first voltage threshold, the controller 511 continues to control the output voltage of the photovoltaic inverter 510 so that the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold.

[0069] S502: After controlling the first switch K1 to close, the controller 511 detects the voltage difference across the second switch K2. When the voltage difference across the second switch K2 is greater than the second voltage threshold and less than or equal to the output voltage of the photovoltaic inverter 510, the controller 511 controls the output voltage of the photovoltaic inverter 510 to increase to a value greater than or equal to the third voltage threshold, so that the photovoltaic inverter 510 supplies power to the load 300.

[0070] Among them, the second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human body safety voltage threshold. The embodiment of the present application does not limit the specific values ​​of the second voltage threshold and the third voltage threshold.

[0071] In the control method of the photovoltaic power generation system provided in the embodiment of the present application, when the power grid 400 is out of power and the output voltage of the photovoltaic inverter 510 is controlled to be less than or equal to the first voltage threshold, the controller 511 controls the first switch K1 to be closed and the second switch K2 to be opened. The AC power transmitted from the first switch K1 to the second switch K2 is used to detect the adhesion fault of the second switch K2, thereby improving the accuracy of the fault detection of the second switch K2. Secondly, since the output voltage of the photovoltaic inverter 510 is less than or equal to the first voltage threshold, and the first voltage threshold is greater than zero and less than or equal to the human safety voltage threshold, in the event of an adhesion fault in the second switch K2, the voltage of the AC power output by the second switch K2 to the power grid 400 will also be less than or equal to the human safety voltage threshold, which will not cause harm to the power grid maintenance personnel, meets the safety compliance risk requirements, and can ensure the safety of the photovoltaic power generation system 500. In addition, compared with the above-mentioned photovoltaic power generation system 100 when it is started, the on-grid and off-grid switching device 120 is disconnected from the power grid 400 by two switches connected in series to achieve isolation of the photovoltaic power generation system 100 from the power grid 400, and the two switches are respectively controlled by two driving circuits. When the photovoltaic power generation system 500 is started off-grid, the on-grid and off-grid switching device 520 can be disconnected from the power grid 400 by a second switch K2, that is, a single switch, to achieve isolation of the photovoltaic power generation system 500 from the power grid 400. There is no need to control the second switch K2 through two driving circuits. The on-grid and off-grid switching device 520 has a simple structure, low cost, and high reliability. Finally, when the voltage difference between the two ends of the second switch K2 is greater than the second voltage threshold and less than or equal to the voltage value of the output voltage of the photovoltaic inverter 510, the controller 511 determines that there is no adhesion fault in the second switch K2. Then, the controller controls the output voltage of the photovoltaic inverter 510 to increase to greater than or equal to the third voltage threshold, so that the photovoltaic inverter 510 supplies power to the load 300. The solution for detecting whether the second switch K2 is stuck is simpler and can ensure that the photovoltaic inverter 510 does not transmit a higher voltage to the power grid 400 through the second switch K2, thereby ensuring the safety of the photovoltaic power generation system 500.

[0072] In one possible embodiment, Figure 5 As shown, the control method of the photovoltaic power generation system provided in the embodiment of the present application further includes step S503. When executing step S503 and the above step S503, one of them can be executed according to the relationship between the voltage difference across the second switch K2 and the voltage threshold.

[0073] S503: After controlling the first switch K1 to close, the controller 511 detects the voltage difference across the second switch K2. If the voltage difference across the second switch K2 is greater than or equal to zero and less than or equal to a fourth voltage threshold, the controller 511 controls the first switch K1 to open and controls the photovoltaic inverter 510 to shut down. The fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold. This embodiment of the present application uses the example of the fourth voltage threshold being equal to the second voltage threshold for illustrative purposes.

[0074] In the control method for a photovoltaic power generation system provided in an embodiment of the present application, when the voltage difference between the two ends of the second switch K2 is greater than or equal to zero and less than or equal to a fourth voltage threshold, the controller 511 controls the first switch K1 to be disconnected and controls the photovoltaic inverter 510 to be shut down when it is determined that the second switch K2 has a adhesion fault. The solution for detecting whether the second switch K2 is adhesion is simpler and can ensure that the photovoltaic inverter 510 does not transmit a higher voltage to the power grid 400 through the second switch K2, thereby ensuring the safety of the photovoltaic power generation system 500.

[0075] In one possible embodiment, referring to Figure 4 In the photovoltaic power generation system 500 provided in the embodiment of the present application, the grid-connected and off-grid switching device 520 further includes a rectifier circuit 521 and an energy storage device 522. The input end of the rectifier circuit 521 is connected to the input end of the grid-connected and off-grid switching device 520, and the output end of the rectifier circuit 521 is connected to the input end of the energy storage device 522. The energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520. Figure 6 As shown, the control method of the photovoltaic power generation system provided in the embodiment of the present application further includes step S504 and step S505 before the above step S501.

[0076] S504 , before controlling the output voltage of the photovoltaic inverter 510 to be less than or equal to the first voltage threshold, the controller 511 controls the output voltage of the photovoltaic inverter 510 to increase from zero to greater than or equal to a third voltage threshold, so as to charge the energy storage device 522 .

[0077] S505: After controlling the photovoltaic inverter 510 to charge the energy storage device 522, the controller 511 controls the output voltage of the photovoltaic inverter 510 to decrease to less than or equal to the first voltage threshold if the voltage of the energy storage device 522 is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device 522 is less than or equal to the voltage fluctuation threshold. The specific values ​​of the fifth voltage threshold and the voltage fluctuation threshold are not limited in this embodiment of the present application.

[0078] In a possible embodiment, the energy storage device 522 is used to supply power to the grid-connected / off-grid switching device 520 from a first moment to a second moment, wherein the first moment is when the voltage of the energy storage device 522 is greater than or equal to a fifth voltage threshold, and the voltage fluctuation of the energy storage device 522 is less than or equal to the voltage fluctuation threshold, and the energy storage device 522 is fully charged, for example Figure 3 The second moment is the moment when the output voltage of the photovoltaic inverter 510 increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold, for example Figure 3 At moment c in the figure, it can be understood that the energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520 in the time period between moment f and moment c, thereby avoiding the situation where the output voltage of the photovoltaic inverter 510 is less than the third voltage threshold and the grid-connected and off-grid switching device 520 cannot work normally, which can improve the reliability of the grid-connected and off-grid switching device 520 and the reliability of the photovoltaic power generation system 500.

[0079] In the control method of the photovoltaic power generation system provided in the embodiment of the present application, the grid-connected and off-grid switching device 520 also includes an energy storage device 522. The controller 511 first controls the photovoltaic inverter 510 to charge the energy storage device 522. When the voltage of the energy storage device 522 is greater than or equal to the fifth voltage threshold, and the voltage fluctuation of the energy storage device 522 is less than or equal to the voltage fluctuation threshold, and the energy storage device 522 is fully charged, the output voltage of the photovoltaic inverter 510 is controlled to be reduced to less than or equal to the first voltage threshold. The energy storage device 522 is used to supply power to the grid-connected and off-grid switching device 520, thereby preventing the grid-connected and off-grid switching device 520 from malfunctioning when the output voltage of the photovoltaic inverter 510 is less than the third voltage threshold. This can improve the reliability of the grid-connected and off-grid switching device 520 and the reliability of the photovoltaic power generation system 500.

[0080] Based on this, Figure 7As shown, an embodiment of the present application further provides a photovoltaic inverter 600, which includes a controller 610, an inverter circuit 620, a first switch K1, and a second switch K2. The input end of the inverter circuit 620 is connected to the photovoltaic array 200, the output end of the inverter circuit 620 is connected to one end of the first switch K1, and the other end of the first switch K1 is connected to one end of the second switch K2. The other end of the first switch K1 is also connected to the load 300, and the other end of the second switch K2 is connected to the power grid 400. The controller 610 is configured to control the first switch K1 to close and the second switch K2 to open when the power grid 400 is out of power and the output voltage of the inverter circuit 620 is less than or equal to a first voltage threshold. The first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold. The controller 610 is also used to detect the voltage difference across the second switch K2 after controlling the first switch K1 to close. When the voltage difference across the second switch K2 is greater than the second voltage threshold and less than or equal to the voltage value of the output voltage of the inverter circuit 620, the controller 610 is used to control the output voltage of the inverter circuit 620 to increase to equal to the third voltage threshold so that the photovoltaic inverter 600 supplies power to the load. The second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold.

[0081] In one possible embodiment, referring to Figure 7 The controller 610 is further configured to detect a voltage difference across the second switch K2 after controlling the first switch K1 to close, and control the first switch K1 to open and control the photovoltaic inverter 600 to shut down when the voltage difference across the second switch K2 is greater than or equal to zero and less than or equal to a fourth voltage threshold. The fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

[0082] In one possible embodiment, referring to Figure 7 The photovoltaic inverter 600 further includes a rectifier circuit 630 and an energy storage device 640. The input of the rectifier circuit 630 is connected to the output of the inverter circuit 620, and the output of the rectifier circuit 630 is connected to the input of the energy storage device 640. The energy storage device 640 is used to supply power to the photovoltaic inverter 600. The controller 610 is further configured to control the output voltage of the inverter circuit 620 to increase from zero to a value greater than or equal to a third voltage threshold before controlling the output voltage of the inverter circuit 620 to be less than or equal to the first voltage threshold, thereby charging the energy storage device 640. The controller 610 is further configured to control the output voltage of the inverter circuit 620 to decrease to a value less than or equal to the first voltage threshold after controlling the output voltage of the inverter circuit 620 to be less than or equal to the first voltage threshold, if the voltage of the energy storage device 640 is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device 640 is less than or equal to the voltage fluctuation threshold after controlling the inverter circuit 620 to charge the energy storage device 640.

[0083] In one possible embodiment, the energy storage device 640 is used to supply power to the photovoltaic inverter 600 from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device 640 is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device 640 is less than or equal to the voltage fluctuation threshold, and the second moment is the moment when the output voltage of the inverter circuit 620 increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

[0084] In a possible embodiment, the energy storage device 640 includes a capacitor or a lithium battery.

[0085] It can be understood that in the photovoltaic inverter 600, the controller 610 is equivalent to the controller 511 in the above-mentioned photovoltaic power generation system 500, the inverter circuit 620 is equivalent to the photovoltaic inverter 510 in the above-mentioned photovoltaic power generation system 500, and the circuit composed of the first switch K1, the second switch K2, the rectifier circuit 630 and the energy storage device 640 is equivalent to the grid-connected and off-grid switching device 520 in the above-mentioned photovoltaic power generation system 500. The above detailed description of the photovoltaic power generation system 500 and the analysis of the beneficial effects can all be correspondingly referred to the control method and photovoltaic inverter 600 of the photovoltaic power generation system, and the embodiments of the present application will not be repeated here.

[0086] The above is only a specific embodiment of the present application, but the scope of protection of this application is not limited to this. Any changes or substitutions within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A photovoltaic power generation system, characterized in that: The photovoltaic power generation system comprises a photovoltaic inverter and an on-grid and off-grid switching device, wherein the input end of the photovoltaic inverter is used to be connected to a photovoltaic array, and the output end of the photovoltaic inverter is connected to the input end of the on-grid and off-grid switching device; The photovoltaic inverter includes a controller, and the on-grid and off-grid switching device includes a first switch and a second switch, one end of the first switch is connected to the input end of the on-grid and off-grid switching device, the other end of the first switch is connected to one end of the second switch, the other end of the first switch is also used to connect to the load, and the other end of the second switch is used to connect to the grid; The controller is used to control the first switch to be closed and the second switch to be opened when the power grid is out of power and the output voltage of the photovoltaic inverter is controlled to be less than or equal to a first voltage threshold, and the first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold; The controller is further used to detect the voltage difference across the second switch after controlling the first switch to close, and when the voltage difference across the second switch is greater than a second voltage threshold and less than or equal to the voltage value of the output voltage of the photovoltaic inverter, control the output voltage of the photovoltaic inverter to increase to greater than or equal to a third voltage threshold so that the photovoltaic inverter supplies power to the load, the second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold.

2. The photovoltaic power generation system according to claim 1, characterized in that: The controller is further configured to detect a voltage difference across the second switch after controlling the first switch to close, and control the first switch to open and control the photovoltaic inverter to shut down when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold, wherein the fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

3. The photovoltaic power generation system according to claim 1 or 2, characterized in that: The on-grid and off-grid switching device further comprises a rectifier circuit and an energy storage device, wherein an input end of the rectifier circuit is connected to an input end of the on-grid and off-grid switching device, an output end of the rectifier circuit is connected to an input end of the energy storage device, and the energy storage device is used to supply power to the on-grid and off-grid switching device; The controller is further configured to control the output voltage of the photovoltaic inverter to increase from zero to greater than or equal to the third voltage threshold before controlling the output voltage of the photovoltaic inverter to be less than or equal to the first voltage threshold, so as to charge the energy storage device; The controller is further used to control the output voltage of the photovoltaic inverter to decrease to less than or equal to the first voltage threshold when, after controlling the photovoltaic inverter to charge the energy storage device, the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to a voltage fluctuation threshold.

4. The photovoltaic power generation system according to claim 3, characterized in that: The energy storage device is used to supply power to the grid-connected and off-grid switching device from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment is the moment when the output voltage of the photovoltaic inverter increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

5. The photovoltaic power generation system according to claim 3 or 4, characterized in that: The energy storage device includes a capacitor or a lithium battery.

6. A control method for a photovoltaic power generation system, characterized in that: Applied to a photovoltaic power generation system, the method comprises: When the power grid is out of power, the controller controls the output voltage of the photovoltaic inverter to be less than or equal to a first voltage threshold, controls the first switch to close, and controls the second switch to open, wherein the first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold; After controlling the first switch to close, the controller detects a voltage difference across the second switch, and when the voltage difference across the second switch is greater than a second voltage threshold and less than or equal to a voltage value of an output voltage of the photovoltaic inverter, controls the output voltage of the photovoltaic inverter to increase to a value greater than or equal to a third voltage threshold, so that the photovoltaic inverter supplies power to a load, wherein the second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold; The photovoltaic power generation system comprises the photovoltaic inverter and the on-grid and off-grid switching device, the input end of the photovoltaic inverter is used to be connected to the photovoltaic array, and the output end of the photovoltaic inverter is connected to the input end of the on-grid and off-grid switching device; The photovoltaic inverter includes the controller, and the grid-connected and off-grid switching device includes the first switch and the second switch, one end of the first switch is connected to the input end of the grid-connected and off-grid switching device, the other end of the first switch is connected to one end of the second switch, the other end of the first switch is also used to connect to the load, and the other end of the second switch is used to connect to the grid.

7. The method according to claim 6, characterized in that The method further comprises: After controlling the first switch to close, the controller detects the voltage difference across the second switch, and controls the first switch to open and controls the photovoltaic inverter to shut down when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold, and the fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

8. The method according to claim 6 or 7, characterized in that: The method further comprises: The controller controls the output voltage of the photovoltaic inverter to increase from zero to greater than or equal to the third voltage threshold before controlling the output voltage of the photovoltaic inverter to be less than or equal to the first voltage threshold, so as to charge the energy storage device; After the controller controls the photovoltaic inverter to charge the energy storage device, when the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to a voltage fluctuation threshold, the controller controls the output voltage of the photovoltaic inverter to decrease to less than or equal to the first voltage threshold; The on-grid and off-grid switching device also includes a rectifier circuit and the energy storage device, the input end of the rectifier circuit is connected to the input end of the on-grid and off-grid switching device, the output end of the rectifier circuit is connected to the input end of the energy storage device, and the energy storage device is used to supply power to the on-grid and off-grid switching device.

9. The method according to claim 8, characterized in that The energy storage device is used to supply power to the grid-connected and off-grid switching device from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment is the moment when the output voltage of the photovoltaic inverter increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

10. The method according to claim 8 or 9, characterized in that: The energy storage device includes a capacitor or a lithium battery.

11. A photovoltaic inverter, characterized in that: The photovoltaic inverter comprises a controller, an inverter circuit, a first switch and a second switch, wherein the input end of the inverter circuit is used to connect to the photovoltaic array, the output end of the inverter circuit is connected to one end of the first switch, the other end of the first switch is connected to one end of the second switch, the other end of the first switch is also used to connect to the load, and the other end of the second switch is used to connect to the grid; The controller is used to control the first switch to be closed and the second switch to be opened when the power grid is out of power and the output voltage of the inverter circuit is controlled to be less than or equal to a first voltage threshold, wherein the first voltage threshold is greater than zero and less than or equal to a human safety voltage threshold; The controller is further used to detect the voltage difference across the second switch after controlling the first switch to close, and when the voltage difference across the second switch is greater than a second voltage threshold and less than or equal to the voltage value of the output voltage of the inverter circuit, control the output voltage of the inverter circuit to increase to a third voltage threshold so that the photovoltaic inverter supplies power to the load, the second voltage threshold is greater than zero and less than the first voltage threshold, and the third voltage threshold is greater than the human safety voltage threshold.

12. The photovoltaic inverter according to claim 11, characterized in that: The controller is further configured to detect a voltage difference across the second switch after controlling the first switch to close, and control the first switch to open and control the photovoltaic inverter to shut down when the voltage difference across the second switch is greater than or equal to zero and less than or equal to a fourth voltage threshold, wherein the fourth voltage threshold is greater than zero and less than or equal to the second voltage threshold.

13. The photovoltaic inverter according to claim 11 or 12, characterized in that: The photovoltaic inverter further includes a rectifier circuit and an energy storage device, wherein the input end of the rectifier circuit is connected to the output end of the inverter circuit, the output end of the rectifier circuit is connected to the input end of the energy storage device, and the energy storage device is used to supply power to the photovoltaic inverter; The controller is further configured to control the output voltage of the inverter circuit to increase from zero to greater than or equal to the third voltage threshold before controlling the output voltage of the inverter circuit to be less than or equal to the first voltage threshold, so as to charge the energy storage device; The controller is further used to control the output voltage of the inverter circuit to decrease to less than or equal to the first voltage threshold when, after controlling the inverter circuit to charge the energy storage device, the voltage of the energy storage device is greater than or equal to a fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to a voltage fluctuation threshold.

14. The photovoltaic inverter according to claim 13, characterized in that: The energy storage device is used to supply power to the photovoltaic inverter from a first moment to a second moment, the first moment being the moment when the voltage of the energy storage device is greater than or equal to the fifth voltage threshold and the voltage fluctuation of the energy storage device is less than or equal to the voltage fluctuation threshold, and the second moment being the moment when the output voltage of the inverter circuit increases from less than or equal to the first voltage threshold to greater than or equal to the third voltage threshold.

15. The photovoltaic inverter according to claim 13 or 14, characterized in that: The energy storage device includes a capacitor or a lithium battery.

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