Photovoltaic power generation system and control method thereof

Abstract

The invention provides a photovoltaic power generation system and a control method thereof, a switching circuit used for controlling a grid-connected and off-grid mode is connected between an inverter and an automatic change-over switch ATS, and the ATS is used for realizing switching between the grid side of the switching circuit connected to a power grid or the grid side of the switching circuit connected to an oil generator. When the photovoltaic power generation system operates in the grid-connected mode, if the grid is abnormal, the grid-connected mode is switched to the off-grid mode for operation, namely, the photovoltaic assembly or the energy storage device supplies power to the load. When the photovoltaic assembly or the energy storage device supplies power to the load, namely when the photovoltaic power generation system operates in an off-grid mode, if the photovoltaic assembly or the energy storage device is insufficient in power supply due to some factors, the photovoltaic assembly or the energy storage device is switched to the parallel oil engine mode to operate. Through the switching process, continuous and stable load power supply of the photovoltaic power generation system during switching of different power supplies can be realized.

Description

Technical Field

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

[0002] The whole-house backup power system is mainly composed of an inverter and an on-grid and off-grid controller. It can be powered by a variety of methods such as photovoltaic panels, energy storage devices and power grids to achieve stable power supply for household loads. With the development of the photovoltaic and energy storage power generation industries, household green power solutions have gradually become more perfect. The configuration of oil generators in the whole-house backup power system (the backup power system is the photovoltaic power generation system) can further improve the continuity and reliability of the load power supply. For the backup power system composed of photovoltaics, energy storage, and oil generators, how to ensure the continuous and stable power supply to the load when switching between different power sources is a technical problem that urgently needs to be solved in this field. Summary of the invention

[0003] The present application provides a photovoltaic power generation system and a control method thereof, which are used to achieve continuous and stable load power supply when the photovoltaic power generation system switches between different power supply sources.

[0004] In the first aspect, the present application provides a photovoltaic power generation system, including: an inverter, an on-grid and off-grid controller and an automatic transfer switch ATS, and the on-grid and off-grid controller includes: a switch circuit and a control circuit. The DC side of the inverter is used to connect to a photovoltaic module or an energy storage device, and the AC side of the inverter is connected to the inverter side of the switch circuit. The ATS is used to switch between the grid side of the switch circuit being connected to the grid or the grid side of the switch circuit being connected to an oil generator. The control circuit is used to: when the switch circuit is in a closed state and the state of the ATS is connected to the grid, that is, when the photovoltaic power generation system is operating in the grid-connected mode, if the voltage on the grid side is less than or equal to the undervoltage protection voltage value, that is, the grid is abnormal, then the switch circuit is disconnected, the inverter is controlled to switch to the voltage source mode, and the off-grid controller is switched to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic components or energy storage devices supply power to the load, the photovoltaic power generation system operates in off-grid mode, that is, when the switch circuit is in the disconnected state, if the photovoltaic components or energy storage devices are insufficiently powered due to certain factors, the oil generator start command is issued. If the oil generator start command is received, the oil generator is controlled to operate. If the ATS is in the state of connecting to the oil generator and the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed, the inverter is controlled to switch to the current source mode, and the off-grid controller is switched to the oil generator mode.

[0005] In the present application, when the photovoltaic power generation system is operating in the grid-connected mode, if the grid is abnormal, the photovoltaic power generation system switches to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, that is, when the photovoltaic power generation system is operating in the off-grid mode, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, the oil generator start command is issued, and the photovoltaic power generation system switches to the oil generator mode. Through the above switching process, the photovoltaic power generation system can achieve continuous and stable load power supply when switching between different power supply sources.

[0006] In some embodiments of the present application, the control circuit is also used for: when the photovoltaic power generation system is operating in parallel with the oil generator mode, that is, when the switch circuit is in a closed state and the ATS is in the state of connecting to the oil generator, if the oil generator fails, or when the photovoltaic component or the energy storage device recovers to the point where it can supply power to the load, an oil generator stop command will be issued; if an oil generator stop command is received, the switch circuit will be disconnected, the inverter will be controlled to switch to the voltage source mode, the oil generator will be controlled to shut down, and the off-grid controller will be switched to the off-grid mode, that is, the photovoltaic component or the energy storage device will be used to power the load to ensure the stability of the load power supply.

[0007] In some embodiments of the present application, the control circuit is also used for: when the photovoltaic power generation system is operating in the oil generator mode, that is, when the switch circuit is in a closed state, and the state of the ATS is connected to the oil generator, if the power grid returns to normal, that is, if the ATS detects that the voltage of the power grid is greater than the threshold, before the ATS switches to the grid side of the switch circuit to connect to the grid, if the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected, and the inverter is controlled to switch to the voltage source mode, that is, the photovoltaic power generation system is first switched to the off-grid mode. Afterwards, when the photovoltaic power generation system is operating in the off-grid mode, that is, when the switch circuit is in a disconnected state, and the state of the ATS is connected to the grid, if the voltage on the grid side is greater than the undervoltage protection voltage value, it means that the grid has returned to normal, the switch circuit is closed, and the inverter is controlled to switch to the current source mode, that is, the photovoltaic power generation system is switched to the grid-connected mode to ensure the stability of the load power supply.

[0008] In some embodiments of the present application, the grid-connected and off-grid controller includes: an inverter side port and a grid side port; the inverter side port is connected to the AC side of the inverter, and the grid side port is used to connect to the ATS. The switching circuit includes: a first relay and a second relay connected in series; the first relay is connected to the inverter side port, and the second relay is connected to the grid side port. When the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode or the oil-connected mode, that is, when it is detected that the voltage on the grid side is greater than the undervoltage protection voltage value, in order to ensure the stability of the power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage on the inverter side and the voltage on the grid side, and close the switch circuit after the synchronization conditions are met. Specifically, when the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, it sends a synchronization command to the inverter and closes the first relay. After receiving the synchronization command, the inverter switches to the VSG control mode. The inverter adjusts the amplitude and frequency of the output voltage according to the grid-side voltage information, and can also adjust the phase. After the control circuit detects that the difference in the voltage amplitude, phase and frequency on the grid side and the inverter side meets the conditions, it means that the voltage on the inverter side is synchronized with the voltage on the grid side. The control circuit closes the second relay to complete the closed switch circuit operation.

[0009] In other embodiments of the present application, a system controller may also be included, which is mainly used for system communication transmission, power scheduling, information reporting and other functions. Generally, the system controller is connected to the inverter and the grid-connected and off-grid controller through an RS485 communication cable. The system control can be integrated inside the grid-connected and off-grid controller, or the system controller can also be set outside the grid-connected and off-grid controller. The system controller is used to send the status of the ATS to the control circuit as being connected to the grid or connected to the oil generator, and to send the oil generator start command or oil generator stop command to the control circuit.

[0010] In the second aspect, the present application provides a control method for a photovoltaic power generation system, including: when the switch circuit is in a closed state and the state of the ATS connected to the switch circuit is connected to the grid, that is, when the photovoltaic power generation system is operating in the grid-connected mode, if the voltage on the grid side of the switch circuit is less than or equal to the undervoltage protection voltage value, that is, the grid is abnormal, then the switch circuit is disconnected, the inverter is controlled to switch to the voltage source mode, and the photovoltaic power generation system is switched to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, the photovoltaic power generation system is operated in the off-grid mode, that is, when the switch circuit is in a disconnected state, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, an oil generator start-up instruction is issued, and if the oil generator start-up instruction is received, the oil generator is controlled to operate, and if the state of the ATS is connected to the oil generator and the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed, the inverter is controlled to switch to the current source mode, and the photovoltaic power generation system is switched to the oil generator mode.

[0011] The present application provides the above-mentioned control method. When the photovoltaic power generation system is operating in the grid-connected mode, if the grid is abnormal, the photovoltaic power generation system switches to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, that is, when the photovoltaic power generation system is operating in the off-grid mode, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, the oil generator start command is issued, and the photovoltaic power generation system switches to the oil generator mode. Through the above-mentioned switching process, the continuous stability of the load power supply can be achieved when the photovoltaic power generation system switches between different power supply sources.

[0012] In some embodiments of the present application, it also includes: when the photovoltaic power generation system is operating in parallel with the oil generator mode, that is, when the switch circuit is in a closed state and the state of the ATS is connected to the oil generator, if the oil generator fails, or the photovoltaic component or the energy storage device recovers to the point where it can supply power to the load, an oil generator stop command will be issued; if the oil generator stop command is received, the switch circuit will be disconnected, the inverter will be controlled to switch to the voltage source mode, the oil generator will be controlled to stop, and the photovoltaic power generation system will be switched to the off-grid mode, that is, the photovoltaic component or the energy storage device will be used to power the load to ensure the stability of the load power supply.

[0013] In some embodiments of the present application, it also includes: when the photovoltaic power generation system is operating in the oil generator mode, that is, when the switch circuit is in a closed state, and the state of the ATS is connected to the oil generator, if the power grid returns to normal, that is, if the ATS detects that the voltage of the power grid is greater than the threshold, before the ATS switches to the grid side of the switch circuit to connect to the grid, if the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected, and the inverter is controlled to switch to the voltage source mode, that is, the photovoltaic power generation system is first switched to the off-grid mode. Afterwards, when the photovoltaic power generation system is operating in the off-grid mode, that is, when the switch circuit is in a disconnected state, and the state of the ATS is connected to the grid, if the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed, and the inverter is controlled to switch to the current source mode, that is, the photovoltaic power generation system is switched to the grid-connected mode to ensure the stability of the load power supply.

[0014] In some embodiments of the present application, when the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode or the oil-connected mode, that is, when it is detected that the voltage on the grid side is greater than the undervoltage protection voltage value, in order to ensure the stability of power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage on the inverter side with the voltage on the grid side, and close the switch circuit after the synchronization condition is met. Specifically, when it is detected that the voltage on the grid side is greater than the undervoltage protection voltage value, a synchronization instruction is sent to the inverter, and the first relay connected to the AC side of the inverter is closed. After receiving the synchronization instruction, the inverter switches to the VSG control mode. The inverter adjusts the amplitude and frequency of the output voltage according to the grid-side voltage information, and can also adjust the phase. After the control circuit detects that the difference in the voltage amplitude, phase and frequency on the grid side and the inverter side meets the conditions, it means that the voltage on the inverter side is synchronized with the voltage on the grid side, and the control circuit closes the second relay connected to the ATS to complete the closed switch circuit operation.

[0015] In a third aspect, the present application provides a photovoltaic power generation system, including an inverter and an ATS, wherein the inverter includes: an inverter circuit, a first switch circuit, a grid-side port, and a control circuit. The DC side of the inverter circuit is used to connect to a photovoltaic module or an energy storage device, and the first switch circuit is connected between the AC side of the inverter circuit and the grid-side port. The ATS is used to switch between connecting the grid-side port to the grid or connecting the grid-side port to the oil generator. The control circuit is used to: when the first switch circuit is in a closed state and the state of the ATS is connected to the grid, that is, when the photovoltaic power generation system is operating in grid-connected mode, if the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, that is, the grid is abnormal, then the first switch circuit is disconnected, the inverter circuit is controlled to switch to the voltage source mode, and the photovoltaic power generation system is switched to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic power generation system is operating in off-grid mode, that is, when the first switch circuit is in the disconnected state, if the photovoltaic components or the energy storage device are insufficiently powered due to certain factors, the oil generator is controlled to operate. If the ATS is in the state of connecting to the oil generator and the voltage of the grid-side port is greater than the undervoltage protection voltage value, the first switch circuit is closed, the inverter circuit is controlled to switch to the current source mode, and the photovoltaic power generation system is switched to the oil parallel generator mode.

[0016] In the present application, when the photovoltaic power generation system is operating in the grid-connected mode, if the grid is abnormal, the photovoltaic power generation system switches to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, that is, when the photovoltaic power generation system is operating in the off-grid mode, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, the photovoltaic power generation system switches to the oil-connected mode. Through the above switching process, the photovoltaic power generation system can achieve continuous and stable load power supply when switching between different power supply sources.

[0017] In some embodiments of the present application, the control circuit is also used for: when the photovoltaic power generation system is operating in parallel with the oil generator mode, that is, when the first switch circuit is in a closed state and the ATS is in the state of connecting to the oil generator, if the oil generator fails, or the photovoltaic component or the energy storage device is restored to the point where it can supply power to the load, then the first switch circuit is disconnected, the inverter circuit is controlled to switch to the voltage source mode, the oil generator is controlled to shut down, and the photovoltaic power generation system is switched to the off-grid mode, that is, the photovoltaic component or the energy storage device is used to power the load to ensure the stability of the load power supply.

[0018] In some embodiments of the present application, the control circuit is also used for: when the photovoltaic power generation system is operating in the oil generator mode, that is, when the first switch circuit is in a closed state, and the state of the ATS is connected to the oil generator, if the power grid returns to normal, that is, if the ATS detects that the voltage of the power grid is greater than the threshold, before the ATS switches to the grid-side port to connect to the grid, if the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, the first switch circuit is disconnected, and the inverter circuit is controlled to switch to the voltage source mode, that is, the photovoltaic power generation system is first switched to the off-grid mode. Afterwards, when the photovoltaic power generation system is operating in the off-grid mode, that is, when the first switch circuit is in a disconnected state, and the state of the ATS is connected to the grid, if the voltage of the grid-side port is greater than the undervoltage protection voltage value, it means that the power grid has returned to normal, the first switch circuit is closed, and the inverter circuit is controlled to switch to the current source mode, that is, the photovoltaic power generation system is switched to the grid-connected mode to ensure the stability of the load power supply.

[0019] In some embodiments of the present application, the photovoltaic power generation system further includes an off-grid port and a second switch circuit, the off-grid port is used to connect to the backup power load, and when the photovoltaic power generation system is running, the controller controls the second switch circuit to be in a closed state. When the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode or the oil-connected mode, that is, when it is detected that the voltage of the grid-side port is greater than the undervoltage protection voltage value, in order to ensure the stability of power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage of the off-grid port with the voltage of the grid-side port, and close the first switch circuit after the synchronization condition is met. Specifically, when the control circuit detects that the voltage of the grid-side port is greater than the undervoltage protection voltage value, the inverter circuit controls the inverter circuit to switch to the VSG control mode, and the inverter circuit adjusts the amplitude and frequency of the output voltage according to the voltage information of the grid-side port, and can also adjust the phase. After the control circuit detects that the difference in the voltage amplitude, phase and frequency of the grid-side port and the off-grid port meets the conditions, it indicates that the voltage of the off-grid port is synchronized with the voltage of the grid-side port, and controls the first switch circuit to close, and completes the operation of closing the first switch circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a networking architecture of the prior art;

[0021] Figure 2A schematic diagram of another networking architecture of the prior art;

[0022] Figure 3 A schematic diagram of a photovoltaic power generation system provided in an embodiment of the present application;

[0023] Figure 4a A schematic diagram of the circuit structure of a single-phase on-grid and off-grid controller provided in an embodiment of the present application;

[0024] Figure 4b A schematic diagram of the circuit structure of a three-phase grid-connected and off-grid controller provided in an embodiment of the present application;

[0025] Figure 5 A schematic diagram of switching between different working modes of a photovoltaic power generation system provided in an embodiment of the present application;

[0026] Figure 6 A schematic diagram of a process of switching between different working modes of a photovoltaic power generation system provided in an embodiment of the present application;

[0027] Figure 7 Another structural schematic diagram of a photovoltaic power generation system provided in an embodiment of the present application;

[0028] Figure 8 Another structural schematic diagram of a photovoltaic power generation system provided in an embodiment of the present application;

[0029] Fig. 9 Another schematic diagram of the structure of a photovoltaic power generation system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as being limited to the embodiments described herein; on the contrary, these embodiments are provided to make the present application more comprehensive and complete, and to fully convey the concepts of the example embodiments to those skilled in the art. The same figure marks in the figures represent the same or similar structures, and thus their repeated descriptions will be omitted. The words expressing position and direction described in this application are all explained using the accompanying drawings as examples, but changes may be made as needed, and all changes are included in the scope of protection of this application. The drawings of this application are only used to illustrate the relative position relationship and do not represent the true proportions.

[0031] It should be noted that specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in a variety of other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific implementation methods disclosed below. The subsequent description of the specification is a preferred implementation method for implementing the present application, but the description is for the purpose of illustrating the general principles of the present application and is not intended to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0032] In order to facilitate understanding of the embodiments of the present application, the relevant technologies involved in the embodiments of the present application are first introduced below.

[0033] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to be used as limitations on the present application. As used in the specification and appended claims of the present application, the singular expressions "one", "a kind of" and "the" are intended to also include expressions such as "one or more", unless there is a clear indication to the contrary in the context. It should also be understood that in the following embodiments of the present application, "at least one" refers to one, two or more than two.

[0034] References to "one embodiment" and the like described in this specification mean that a particular feature, structure or characteristic described in conjunction with the embodiment is included in one or more embodiments of the present application. Thus, the phrases "in one embodiment", "in some embodiments", "in other embodiments", etc. that appear at different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0035] Reference Figure 1 At present, in the photovoltaic power generation system that uses oil generators, power grids, photovoltaic modules, and energy storage devices to form the power supply, the power supply and the load are connected to the networking architecture of the photovoltaic power generation system through AC cables. The photovoltaic power generation system switches the power supply to supply power to the load by detecting the voltage changes of the power grid, the changes in the amount of electricity stored in the energy storage device, and the changes in the power generation capacity of the photovoltaic modules. Since the oil generator and the power grid are directly connected to the AC cable, the photovoltaic power generation system can only determine that the power grid has lost power and switch to the oil generator for power supply when it detects the voltage change of the AC cable. As a result, the load power supply is interrupted during the switch from power grid power supply to power supply from the oil generator, and seamless switching cannot be achieved, so the continuity of load power supply cannot be guaranteed. In addition, there may be a large current shock when the power supply is switched, and the stability of the load power supply cannot be guaranteed. Reference Figure 2In the prior art, a power converter can be added between the oil generator and the AC cable to control the oil generator to connect to and exit the photovoltaic power generation system. The added power converter will increase the cost of the photovoltaic power generation system and the complexity of control.

[0036] Based on this, the photovoltaic power generation system and control method thereof provided in the embodiments of the present application are used to ensure the stability of load power supply when the photovoltaic power generation system switches between different power supply sources.

[0037] Reference Figure 3 , the photovoltaic power generation system provided in the embodiment of the present application includes an inverter, an on-grid and off-grid controller and an automatic transfer switch (automatic transfer switch, ATS). The backup power system may also include a system controller, which is mainly used for system communication transmission, power scheduling, information reporting and other functions. Generally, the system controller is connected to the inverter and the on-grid and off-grid controller through an RS485 communication cable. The inverter is connected between the DC source and the on-grid and off-grid controller. The DC side of the inverter is used to connect to the DC source. The DC source can specifically be a photovoltaic module. The DC source can also be an energy storage device. The AC side of the inverter is connected to the inverter side of the on-grid and off-grid controller. The inverter is used to convert the DC power provided by the photovoltaic module or the energy storage device into AC power. The inverter may specifically include an inverter circuit DC / AC, and may also include a DC conversion circuit DC / DC. The DC conversion circuit DC / DC is used to convert the DC power provided by the photovoltaic module into power, and the inverter circuit DC / AC is used to convert the DC power provided by the DC conversion circuit DC / DC or the DC power provided by the energy storage device into AC power. The on-grid and off-grid controller may specifically include a switch circuit, the inverter side of the switch circuit is connected to the AC side of the inverter, and the grid side of the switch circuit is connected to the ATS. The ATS is used to switch between the grid side of the switch circuit being connected to the grid or the grid side of the switch circuit being connected to the oil generator. In the present application, the on-grid and off-grid controller is connected between the inverter and the ATS, the grid or the oil generator is connected through the ATS to provide AC power to the photovoltaic power generation system, and the photovoltaic module or the energy storage device is connected to the inverter to provide DC power to the photovoltaic power generation system. Specifically, when the ATS detects that the voltage of the grid is normal, it switches its state to connect to the grid. When the voltage of the grid is abnormal, for example, the voltage of the grid is less than a threshold, if the ATS detects that the voltage output by the oil generator is normal, for example, the voltage is greater than a threshold, the ATS will automatically switch its state to connect to the oil generator. By connecting the ATS on the grid side of the on-grid and off-grid controller, switching between the two grid-connected power sources, the grid and the oil generator, can be achieved without complex control logic.

[0038] In order to meet the requirements of power safety, the switch circuit generally includes a two-stage switch, namely a first relay T1 and a second relay T2 connected in series. Figure 4a and Figure 4bThe on-grid and off-grid controller generally includes four ports, specifically: the first power-taking port, the second power-taking port, the inverter side port and the grid side port. Among them, the first power-taking port is used to connect to the backup power load, the second power-taking port is used to connect to the non-backup power load, the inverter side port is used to connect to the AC side of the inverter, and the grid side port is used to connect to the ATS. The first relay T1 is connected to the first power-taking port and the inverter side port respectively, and the second relay T2 is connected to the second power-taking port and the grid side port respectively. Figure 4a The grid-connected and off-grid controller provided in this application can adopt a single-phase grid-connected and off-grid controller, or, referring to Figure 4b The grid-connected and off-grid controller provided in the present application may also adopt a three-phase grid-connected and off-grid controller. In addition, the grid-connected and off-grid controller may also include an NPE relay T3 connected between the neutral line N and the ground line PE, and a bypass switch T4 connected between the inverter side port and the grid side port.

[0039] The on-grid and off-grid controller also includes a control circuit, which can determine the working mode of the photovoltaic power generation system according to the voltage on the grid side of the switch circuit, the voltage on the inverter side of the switch circuit, and the type of AC power supply connected sent by the ATS (i.e., the state of the ATS is connected to the grid or the state of the ATS is connected to the oil generator). Specifically, the working modes of the photovoltaic power generation system are mainly divided into: grid-connected mode, oil-connected mode, and off-grid mode. In addition, the control circuit can switch between the grid-connected mode (including the grid-connected mode and the oil-connected mode) and the off-grid mode of the photovoltaic power generation system by controlling the closing or closing of the two-stage switch in the switch circuit, thereby ensuring the continuity of load power supply.

[0040] In the present application, when the voltage of the control circuit on the grid side is greater than the undervoltage protection voltage value, and the state of the ATS is connected to the grid, the control switch circuit is in a closed state, the inverter is controlled to operate in current source mode, and the oil generator is controlled to shut down, so that the photovoltaic power generation system is connected to the grid mode to supply power to the load. Among them, the undervoltage protection voltage value is generally set to the voltage value of the first-level undervoltage protection point, for example, it can be set to 0.7Un, and Un is the rated value of the grid voltage. Only when the voltage on the grid side is greater than the undervoltage protection voltage value can it be connected to the grid. Once the voltage on the grid side is less than the undervoltage protection voltage value, it cannot be connected to the grid and can only be switched to the off-grid mode. When the voltage of the control circuit on the grid side is greater than the undervoltage protection voltage value, and the state of the ATS is connected to the oil generator, the control switch circuit is in a closed state, the inverter is controlled to operate in current source mode, and the oil generator is controlled to operate, so that the photovoltaic power generation system is connected to the oil generator mode to supply power to the load. When the voltage of the control circuit on the grid side is less than or equal to the undervoltage protection voltage value, and the voltage on the inverter side is greater than the minimum off-grid output voltage value, the control switch circuit is in the disconnected state, and the inverter is controlled to operate in voltage source mode, and the oil generator is controlled to stop, so that the photovoltaic power generation system operates in off-grid mode to supply power to the load. Among them, the minimum off-grid output voltage value is the minimum voltage value output by the inverter when it is off-grid, for example, 0.6Un can be selected. Off-grid operation can only be performed when the voltage on the inverter side is greater than the minimum off-grid output voltage value.

[0041] In the present application, the control circuit can control the inverter to operate in current source mode or voltage source mode by sending an on-grid switching signal (DO1 signal) to the inverter. Specifically, the on-grid switching signal may include a first high-level signal indicating on-grid operation and a first low-level signal indicating off-grid operation. The control circuit sends a first high-level signal or a first low-level signal to the inverter, and the inverter switches to voltage source mode when receiving the first low-level signal, and switches to current source mode when receiving the first high-level signal.

[0042] In the present application, the ATS can send an ATS switching state signal (DO2 signal) to the system controller, and the system controller sends the AC power type to the inverter and the grid-connected and off-grid controller through RS485 communication, so that the grid-connected and off-grid controller determines that the state of the ATS is connected to the grid or the oil generator, so that the grid-connected and off-grid controller determines the working mode of the photovoltaic power generation system. When the inverter receives the first high-level signal indicating grid-connected operation, according to the received AC power type, the output voltage is selected to meet the voltage protection parameters of the currently connected grid or oil generator. Specifically, the ATS switching state signal may include a second high-level signal indicating access to the oil generator, and a second low-level signal indicating access to the grid. When the ATS detects that the voltage of the grid is greater than the threshold, it determines that the state of the ATS is connected to the grid, and then sends a second low-level signal to the system controller, and the system controller forwards the received signal to the control circuit, so that the control circuit determines that the state of the ATS is connected to the grid. When the ATS detects that the voltage of the oil generator is greater than the threshold, it determines that the state of the ATS is connected to the oil generator, and then sends a second high-level signal to the system controller, and the system controller forwards the received signal to the control circuit, so that the control circuit determines that the state of the ATS is connected to the oil generator.

[0043] In the present application, the oil generator can send an oil generator fault signal (DO3 signal) to the system controller so that the system controller can formulate the oil generator start-stop strategy by integrating system data such as energy storage capacity and remaining power (SOC), photovoltaic module power, inverter overload status, oil generator status, and power grid status. The system controller sends the oil generator start-stop command to the grid-connected and off-grid controller through RS485 communication, so that the grid-connected and off-grid controller can determine the working mode of the photovoltaic power generation system and control the operation or shutdown of the oil generator. Specifically, the oil generator fault signal may include a third high-level signal indicating that the oil generator is faulty, and a third low-level signal indicating that the oil generator is normal. When the oil generator detects a fault, it sends a third high-level signal to the system controller, and the system controller sends an oil generator stop command to the control circuit. When the oil generator is normal, it sends a third low-level signal to the system controller. The system controller can determine that the oil generator needs to be started based on system data such as energy storage capacity and remaining power (SOC), photovoltaic module power, inverter overload status, oil generator status, and power grid status, and then send an oil generator start command to the control circuit.

[0044] In the present application, the control circuit can control the oil generator to run or shut down by sending an oil generator start-stop control signal (DO4 signal) to the oil generator. Specifically, the oil generator start-stop control signal may include a fourth high-level signal indicating starting the oil generator, and a fourth low-level signal indicating shutting down. The control circuit sends the fourth high-level signal or the fourth low-level signal to the oil generator, and the oil generator performs a start operation when receiving the fourth high-level signal, and performs a shut down operation when receiving the fourth low-level signal.

[0045] In the present application, the photovoltaic power generation system can quickly transmit the above-mentioned on-grid switching signal, ATS switching status signal, oil engine fault signal, and oil engine start-stop control signal by setting up a signal cable independent of the power cable. Transmitting the above signals through the signal cable can improve the speed and reliability of signal transmission. Specifically, refer to Figure 3 A signal cable for transmitting on-grid and off-grid switching signals can be set between the on-grid and off-grid controller and the inverter, a signal cable for transmitting ATS switching status signals can be set between the ATS and the system controller, a signal cable for transmitting oil engine fault signals can be set between the oil generator and the system controller, and a signal cable for transmitting oil engine start and stop control signals can be set between the on-grid and off-grid controller and the oil generator.

[0046] Reference Figure 5 In the present application, the working mode switching condition of the photovoltaic power generation system is: when the power grid is normal, the photovoltaic power generation system operates in the grid-connected mode. When the photovoltaic power generation system operates in the grid-connected mode, if the power grid is abnormal, that is, the voltage of the power grid is less than the undervoltage protection voltage value, the photovoltaic power generation system switches to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, that is, when the photovoltaic power generation system operates in the off-grid mode, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, the oil generator start command is issued, and the photovoltaic power generation system switches to the oil generator mode.

[0047] When the photovoltaic power generation system is running in parallel with the diesel generator mode, if the diesel generator fails, or the photovoltaic modules or energy storage devices recover to the point where they can supply power to the load, a stop command for the diesel generator will be issued, and the photovoltaic power generation system will switch to off-grid mode, that is, using photovoltaic modules or energy storage devices to supply power to the load.

[0048] When the photovoltaic components or energy storage devices are supplying power to the load, that is, when the photovoltaic power generation system is operating in off-grid mode, if the grid returns to normal, that is, when the voltage of the grid returns to a value greater than the undervoltage protection voltage, the photovoltaic power generation system switches to grid-connected mode.

[0049] When the photovoltaic power generation system is operating in the diesel generator mode, if the power grid returns to normal, the photovoltaic power generation system will first switch to the off-grid mode and then switch to the grid-connected mode.

[0050] Through the above switching logic, seamless switching of power supply in the photovoltaic power generation system can be achieved to ensure continuous and stable power supply to the load.

[0051] The following is a detailed introduction to the judgment logic of each working mode in the photovoltaic power generation system and the switching logic between each working mode.

[0052] Reference Figure 6 After the grid-connected and off-grid controller is powered on, the control circuit first determines whether the voltage on the grid side is greater than the undervoltage protection voltage value. If it is determined that the voltage on the grid side is greater than the undervoltage protection voltage value, the control circuit determines whether the state of the ATS is connected to the grid through the ATS switching state signal fed back by the ATS. If it is determined that the state of the ATS is connected to the grid, the control circuit controls the switch circuit to be in a closed state, and the control circuit sends a first high-level signal indicating grid-connected operation to the inverter, so that the inverter operates in current source mode, and the photovoltaic power generation system operates in grid-connected mode to supply power to the load. If it is determined that the state of the ATS is connected to the oil generator, the control circuit controls the switch circuit to be in a closed state, and the control circuit sends a first high-level signal indicating grid-connected operation to the inverter, so that the inverter operates in current source mode, and the photovoltaic power generation system operates in oil-connected mode to supply power to the load. If it is determined that the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the control circuit determines whether the voltage on the inverter side is greater than the minimum off-grid output voltage value. If it is determined that the voltage on the inverter side is greater than the minimum off-grid output voltage value, the switch circuit is controlled to be in an off state, and the control circuit sends a first low-level signal indicating off-grid operation to the inverter, so that the inverter operates in voltage source mode, and the photovoltaic power generation system operates in off-grid mode to power the load.

[0053] Reference Figure 6 When the photovoltaic power generation system is operating in the grid-connected mode, that is, when the switch circuit is in a closed state and the ATS is in the grid-connected state, if the control circuit detects that the voltage on the grid side is less than or equal to the undervoltage protection voltage value, it means that the grid is faulty, and the control circuit disconnects the switch circuit and sends a first low-level signal indicating off-grid operation to the inverter. The inverter switches to the voltage source mode according to the first low-level signal, and the photovoltaic power generation system switches from the grid-connected mode to the off-grid mode.

[0054] Reference Figure 6When the photovoltaic power generation system is running in off-grid mode, that is, when the switch circuit is in the disconnected state, under the condition that the system controller receives the third low-level signal sent by the oil generator indicating that the oil generator is normal, if the system controller determines that the oil generator needs to be started based on other conditions (such as insufficient power generation of the photovoltaic component or the energy storage device), it will send an oil generator start instruction to the off-grid controller. When the control circuit determines that the oil generator start instruction is received, it sends a fourth high-level signal indicating the start of the oil generator to the oil generator, and the oil generator performs the start operation when receiving the fourth high-level signal. After the oil generator is running, when the ATS detects that the voltage of the oil generator is normal, it switches its state to connect to the oil generator, and sends a second high-level signal indicating the connection of the oil generator to the system controller. The system controller sends a signal that the AC power type is an oil generator to the off-grid controller through RS485 communication. After the oil generator is running, when the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, the control circuit closes the switch circuit and sends a first high-level signal indicating grid-connected operation to the inverter. The inverter switches to the current source mode according to the first high-level signal, and the photovoltaic power generation system switches from the off-grid mode to the oil generator mode.

[0055] Reference Figure 6 When the photovoltaic power generation system is running in the oil generator mode, that is, when the switch circuit is in the closed state and the ATS is in the state of connecting to the oil generator, if the oil generator fails, the third high-level signal indicating the oil generator failure is sent to the system controller. After the system controller receives the oil generator failure signal or determines that the oil generator needs to be stopped based on other conditions (such as the photovoltaic component or energy storage device is restored to the point where it can supply power to the load), it sends the oil generator stop command to the grid-connected and off-grid controller through RS485 communication. When the control circuit receives the oil generator stop command, it disconnects the switch circuit and sends the first low-level signal indicating off-grid operation to the inverter. The inverter switches to the voltage source mode according to the first low-level signal, and the photovoltaic power generation system switches from the oil generator mode to the off-grid mode. Then, the control circuit sends the fourth low-level signal indicating shutdown to the oil generator, and the oil generator performs the shutdown operation according to the fourth low-level signal.

[0056] Reference Figure 6When the photovoltaic power generation system is running in the oil generator mode, that is, when the switch circuit is in the closed state, and the state of the ATS is connected to the oil generator, if the ATS detects that the power grid has returned to normal, that is, the ATS detects that the voltage of the power grid is greater than the threshold, the ATS performs a blanking operation before switching its state to the power grid, that is, the ATS is neither connected to the oil generator nor to the power grid, so that the voltage on the grid side is abnormal. When the control circuit detects that the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the control circuit disconnects the switch circuit and sends a first low-level signal indicating off-grid operation to the inverter. The inverter switches to the voltage source mode according to the first low-level signal, and the photovoltaic power generation system switches from the grid-connected mode to the off-grid mode. Afterwards, the ATS switches to connect to the grid, so that the ATS switches to the state of connecting to the grid, and the ATS sends a second low-level signal indicating that the grid is connected to the system controller. The system controller sends a signal that the AC power type is the grid to the off-grid controller through RS485 communication. When the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, the control circuit closes the switch circuit and sends a first high-level signal indicating grid-connected operation to the inverter. The inverter switches to the current source mode according to the first high-level signal, and the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode.

[0057] Reference Figure 6 When the photovoltaic power generation system is operating in off-grid mode, that is, when the switch circuit is in the disconnected state, if the ATS detects that the voltage of the grid has returned to normal, the ATS switches to the state of connecting to the grid and sends a second low-level signal indicating that the grid is connected to the system controller. The system controller sends a signal that the AC power type is the grid to the off-grid controller through RS485 communication. When the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, the control circuit closes the switch circuit and sends a first high-level signal indicating grid-connected operation to the inverter. The inverter switches to the current source mode according to the first high-level signal, and the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode.

[0058] In some embodiments of the present application, when the photovoltaic power generation system switches from an off-grid mode to a grid-connected mode or a diesel generator mode, when the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, in order to ensure the stability of power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage on the inverter side with the voltage on the grid side, and close the switch circuit after the synchronization conditions are met.

[0059] Specifically, when the control circuit detects that the voltage on the grid side is greater than the undervoltage protection voltage value, the control circuit sends a synchronization command to the inverter and closes the first relay. After receiving the synchronization command, the inverter switches to the virtual synchronous generator (VSG) control mode. The inverter adjusts the amplitude and frequency of the output voltage according to the grid-side voltage information, and can also adjust the phase. After the control circuit detects that the difference in the voltage amplitude, phase and frequency on the grid side and the inverter side meets the conditions, it means that the voltage on the inverter side is synchronized with the voltage on the grid side. The control circuit closes the second relay to complete the closed switch circuit operation.

[0060] Reference Figure 7 In some other embodiments of the present application, the system controller can be integrated into the on-grid and off-grid controller, that is, the function of the system controller is integrated into the on-grid and off-grid controller. At this time, the on-grid and off-grid controller and the inverter are connected via an RS485 communication, and there are four signal cables in the backup power system, specifically including: a signal cable for transmitting on-grid and off-grid switching signals set between the on-grid and off-grid controller and the inverter, a signal cable for transmitting ATS switching status signals set between the ATS and the on-grid and off-grid controller, a signal cable for transmitting oil engine fault signals set between the oil generator and the on-grid and off-grid controller, and a signal cable for transmitting oil engine start-stop control signals set between the on-grid and off-grid controller and the oil generator.

[0061] Reference Figure 8 In some other embodiments of the present application, the photovoltaic power generation system may include multiple inverters, and the grid-connected and off-grid controllers and each inverter are connected to the system controller via an RS485 communication channel, and the grid-connected and off-grid controllers transmit grid-connected and off-grid disconnection signals to each inverter via a signal cable. The control circuit can simultaneously control multiple inverters to operate in current source mode, or simultaneously control multiple inverters to operate in voltage source mode.

[0062] Based on the same inventive concept, the embodiment of the present application also provides a control method for a photovoltaic power generation system, which specifically includes the following steps:

[0063] When the switch circuit is in a closed state and the ATS connected to the switch circuit is connected to the grid, that is, when the photovoltaic power generation system is operating in grid-connected mode, if the voltage on the grid side of the switch circuit is less than or equal to the undervoltage protection voltage value, that is, the grid is abnormal, the switch circuit is disconnected, the inverter is controlled to switch to the voltage source mode, and the photovoltaic power generation system is switched to the off-grid mode, that is, photovoltaic modules or energy storage devices are used to power the load.

[0064] When the photovoltaic components or energy storage devices supply power to the load, the photovoltaic power generation system operates in off-grid mode, that is, when the switch circuit is in the disconnected state, if the photovoltaic components or energy storage devices are insufficiently powered due to certain factors, the oil generator start command is issued. If the oil generator start command is received, the oil generator is controlled to operate. If the ATS is in the state of connecting to the oil generator and the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed, the inverter is controlled to switch to the current source mode, and the photovoltaic power generation system is switched to the oil generator mode.

[0065] In some embodiments of the present application, when the photovoltaic power generation system is operating in parallel with the oil generator mode, that is, when the switch circuit is in a closed state and the ATS is in the state of connecting to the oil generator, if the oil generator fails, or when the photovoltaic components or energy storage devices are restored to the point where they can supply power to the load, an oil generator stop command will be issued. If the oil generator stop command is received, the switch circuit will be disconnected, the inverter will be controlled to switch to the voltage source mode, the oil generator will be controlled to stop, and the photovoltaic power generation system will be switched to the off-grid mode, that is, the photovoltaic components or energy storage devices will be used to supply power to the load.

[0066] In some embodiments of the present application, when the photovoltaic power generation system is operating in the oil generator mode, that is, when the switch circuit is in a closed state and the state of the ATS is connected to the oil generator, if the power grid returns to normal, that is, if the ATS detects that the voltage of the power grid is greater than the threshold, before the ATS switches to the grid side of the switch circuit to connect to the grid, if the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected, and the inverter is controlled to switch to the voltage source mode, that is, the photovoltaic power generation system is first switched to the off-grid mode. Afterwards, when the photovoltaic module or energy storage device supplies power to the load, the photovoltaic power generation system operates in the off-grid mode, that is, when the switch circuit is in a disconnected state and the state of the ATS is connected to the grid, if the voltage on the grid side is greater than the undervoltage protection voltage value, it means that the power grid has returned to normal, the switch circuit is closed, and the inverter is controlled to switch to the current source mode, that is, the photovoltaic power generation system is switched to the grid-connected mode.

[0067] In some embodiments of the present application, when the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode or the oil-connected mode, that is, when it is detected that the voltage on the grid side is greater than the undervoltage protection voltage value, in order to ensure the stability of power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage on the inverter side with the voltage on the grid side, and close the switch circuit after the synchronization condition is met. Specifically, when it is detected that the voltage on the grid side is greater than the undervoltage protection voltage value, a synchronization instruction is sent to the inverter, and the first relay connected to the AC side of the inverter is closed. After receiving the synchronization instruction, the inverter switches to the VSG control mode. The inverter adjusts the amplitude and frequency of the output voltage according to the grid-side voltage information, and can also adjust the phase. After the control circuit detects that the difference in the voltage amplitude, phase and frequency on the grid side and the inverter side meets the conditions, it means that the voltage on the inverter side is synchronized with the voltage on the grid side, and the control circuit closes the second relay connected to the ATS to complete the closed switch circuit operation.

[0068] Based on the same inventive concept, the embodiment of the present application also provides another photovoltaic power generation system, which integrates the functions of the on-grid and off-grid controller into the inverter to form an integrated structure. Fig. 9 , the photovoltaic power generation system specifically includes: an inverter and an ATS, the inverter includes: an inverter circuit DC / AC, a first switch circuit, a grid-side port and a control circuit, and may also include a DC conversion circuit DC / DC. The DC side of the inverter circuit DC / AC is used to connect to a photovoltaic module or an energy storage device through a DC conversion circuit DC / DC, and the first switch circuit is connected between the AC side of the inverter circuit DC / AC and the grid-side port. The DC conversion circuit DC / DC is used to convert the DC power provided by the photovoltaic module, and the inverter circuit DC / AC is used to convert the DC power provided by the DC conversion circuit DC / DC or the DC power provided by the energy storage device into AC power. The ATS is used to switch between connecting the grid-side port to the grid-side port or connecting the grid-side port to the oil generator. The first switch circuit is connected between the inverter circuit DC / AC and the ATS, and the grid or the oil generator is connected through the ATS to provide AC power for the photovoltaic power generation system, and the photovoltaic module or the energy storage device is connected to the inverter to provide DC power for the photovoltaic power generation system. Specifically, when the ATS detects that the voltage of the power grid is normal, it switches its state to connect to the power grid. When the voltage of the power grid is abnormal, for example, the voltage of the power grid is less than the threshold, if the ATS detects that the voltage output by the oil generator is normal, for example, the voltage is greater than the threshold, the ATS will automatically switch its state to connect to the oil generator. The ATS connected to the grid-side port can realize the switching between the two grid-connected power sources, the power grid and the oil generator, without complex control logic.

[0069] Reference Fig. 9, the first switch circuit may specifically include a first relay T1. The inverter may also include an off-grid port and a second switch circuit, and the second switch circuit may specifically include a second relay T2. When the photovoltaic power generation system is running, the controller controls the second switch circuit to be in a closed state. Among them, the off-grid port is used to connect to the backup power load, and the grid-side port is used to connect to the ATS. The first relay T1 is connected between the inverter circuit DC / AC and the grid-side port, and the second relay T2 is connected between the inverter circuit DC / AC and the off-grid port.

[0070] The control circuit can determine the working mode of the photovoltaic power generation system according to the voltage of the off-grid port, the voltage of the grid-side port and the type of AC power supply connected sent by the ATS (i.e., the state of the ATS is connected to the grid or the state of the ATS is connected to the oil generator). Specifically, the working modes of the photovoltaic power generation system are mainly divided into: grid-connected mode, oil-connected mode and off-grid mode. In addition, the control circuit can switch between the grid-connected mode (including grid-connected mode and oil-connected mode) and the off-grid mode of the photovoltaic power generation system by controlling the first switch circuit to close or close, thereby ensuring the continuity of load power supply.

[0071] In the present application, when the voltage of the control circuit at the grid-side port is greater than the undervoltage protection voltage value, and the state of the ATS is connected to the grid, the first switch circuit is controlled to be in a closed state, the inverter circuit is controlled to operate in a current source mode, and the oil generator is controlled to stop, so that the photovoltaic power generation system is connected to the grid mode to supply power to the load. When the voltage of the control circuit at the grid-side port is greater than the undervoltage protection voltage value, and the state of the ATS is connected to the oil generator, the first switch circuit is controlled to be in a closed state, the inverter circuit is controlled to operate in a current source mode, and the oil generator is controlled to operate, so that the photovoltaic power generation system is connected to the oil generator mode to supply power to the load. When the voltage of the control circuit at the grid-side port is less than or equal to the undervoltage protection voltage value, and the voltage of the off-grid port is greater than the minimum off-grid output voltage value, the first switch circuit is controlled to be in an open state, and the inverter circuit is controlled to operate in a voltage source mode, and the oil generator is controlled to stop, so that the photovoltaic power generation system is operated in an off-grid mode to supply power to the load.

[0072] In the present application, the ATS can send an ATS switching state signal (DO2 signal) to the inverter so that the inverter determines that the state of the ATS is connected to the grid or the oil generator, so as to determine the operating mode of the photovoltaic power generation system. Specifically, the ATS switching state signal may include a second high-level signal indicating that the oil generator is connected, and a second low-level signal indicating that the grid is connected. When the ATS detects that the voltage of the grid is greater than the threshold, it determines that the state of the ATS is connected to the grid, and then sends a second low-level signal to the inverter so that the control circuit determines that the state of the ATS is connected to the grid. When the ATS detects that the voltage of the oil generator is greater than the threshold, it determines that the state of the ATS is connected to the oil generator, and then sends a second high-level signal to the inverter so that the control circuit determines that the state of the ATS is connected to the oil generator.

[0073] In the present application, the oil generator can send an oil generator fault signal (DO3 signal) to the inverter so that the inverter can formulate an oil generator start-stop strategy based on system data such as energy storage capacity and remaining power (SOC), photovoltaic module power, inverter overload status, oil generator status, and grid status. Specifically, the oil generator fault signal may include a third high-level signal indicating an oil generator fault and a third low-level signal indicating that the oil generator is normal. When the oil generator detects a fault, it sends a third high-level signal to the inverter. When the oil generator is normal, it sends a third low-level signal to the inverter.

[0074] In the present application, the inverter can control the oil generator to run or shut down by sending an oil generator start-stop control signal (DO4 signal) to the oil generator. Specifically, the oil generator start-stop control signal may include a fourth high-level signal indicating starting the oil generator, and a fourth low-level signal indicating shutting down. The inverter sends a fourth high-level signal or a fourth low-level signal to the oil generator, and the oil generator performs a start operation when receiving the fourth high-level signal, and performs a shut down operation when receiving the fourth low-level signal.

[0075] In the present application, the photovoltaic power generation system can quickly transmit the above-mentioned ATS switching status signal, oil engine fault signal, and oil engine start-stop control signal by setting up a signal cable independent of the power cable. Transmitting the above signals through the signal cable can improve the speed and reliability of signal transmission. Specifically, refer to Fig. 9 A signal cable for transmitting the ATS switching status signal can be set between the ATS and the inverter, a signal cable for transmitting the oil engine fault signal can be set between the oil generator and the inverter, and a signal cable for transmitting the oil engine start-stop control signal can be set between the inverter and the oil generator.

[0076] In the present application, the working mode switching condition of the photovoltaic power generation system is: when the photovoltaic power generation system is operating in the grid-connected mode, if the grid is abnormal, that is, the voltage of the grid is less than the undervoltage protection voltage value, the photovoltaic power generation system switches to the off-grid mode, that is, the photovoltaic module or energy storage device is used to power the load. When the photovoltaic module or energy storage device is powering the load, that is, when the photovoltaic power generation system is operating in the off-grid mode, if the photovoltaic module or energy storage device is insufficiently powered due to certain factors, the oil generator start command is issued, and the photovoltaic power generation system switches to the oil generator mode, that is, the oil generator is used to power the load.

[0077] When the photovoltaic power generation system is running in parallel with the diesel generator mode, if the diesel generator fails, or the photovoltaic modules or energy storage devices recover to the point where they can supply power to the load, a stop command for the diesel generator will be issued, and the photovoltaic power generation system will switch to off-grid mode, that is, using photovoltaic modules or energy storage devices to supply power to the load.

[0078] When the photovoltaic components or energy storage devices are supplying power to the load, that is, when the photovoltaic power generation system is operating in off-grid mode, if the grid returns to normal, that is, when the voltage of the grid returns to a value greater than the undervoltage protection voltage, the photovoltaic power generation system switches to grid-connected mode.

[0079] When the photovoltaic power generation system is operating in the diesel generator mode, if the power grid returns to normal, the photovoltaic power generation system will first switch to the off-grid mode and then switch to the grid-connected mode.

[0080] Through the above switching logic, seamless switching of power supply in the photovoltaic power generation system can be achieved to ensure continuous and stable power supply to the load.

[0081] The following is a detailed introduction to the judgment logic of each working mode in the photovoltaic power generation system and the switching logic between each working mode.

[0082] After the inverter is powered on, the control circuit first determines whether the voltage of the grid-side port is greater than the undervoltage protection voltage value. If it is determined that the voltage of the grid-side port is greater than the undervoltage protection voltage value, the control circuit determines whether the state of the ATS is connected to the grid through the ATS switching state signal fed back by the ATS. If it is determined that the state of the ATS is connected to the grid, the control circuit controls the first switch circuit to be in a closed state, and the control circuit controls the inverter circuit to operate in a current source mode, so that the photovoltaic power generation system is connected to the grid mode to supply power to the load. If it is determined that the state of the ATS is connected to the oil generator, the control circuit controls the first switch circuit to be in a closed state, and the control circuit controls the inverter circuit to operate in a current source mode, so that the photovoltaic power generation system is connected to the oil generator mode to supply power to the load. If it is determined that the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, the first switch circuit is controlled to be in a disconnected state, and the control circuit controls the inverter circuit to operate in a voltage source mode, so that the photovoltaic power generation system is operated in an off-grid mode to supply power to the load.

[0083] When the photovoltaic power generation system is operating in the grid-connected mode, that is, when the first switch circuit is in a closed state and the ATS is in the grid-connected state, if the control circuit detects that the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, it indicates a grid fault, and the control circuit disconnects the first switch circuit and controls the inverter circuit to switch to the voltage source mode at the same time. The photovoltaic power generation system switches from the grid-connected mode to the off-grid mode.

[0084] When the photovoltaic power generation system is operating in off-grid mode, that is, when the first switch circuit is in the disconnected state, under the condition of receiving the third low-level signal sent by the oil generator indicating that the oil generator is normal, if the control circuit determines that the oil generator needs to be started based on other conditions (such as insufficient power generation of the photovoltaic component or the energy storage device), the fourth high-level signal indicating the start of the oil generator is sent to the oil generator, and the oil generator performs the start operation when receiving the fourth high-level signal. After the oil generator is running, when the ATS detects that the voltage of the oil generator is normal, it switches its state to connect to the oil generator and sends the second high-level signal indicating the connection of the oil generator to the inverter. After the oil generator is running, when the control circuit detects that the voltage of the grid-side port is greater than the undervoltage protection voltage value, the control circuit closes the first switch circuit and controls the inverter circuit to switch to the current source mode, and the photovoltaic power generation system switches from the off-grid mode to the oil-connected generator mode.

[0085] When the photovoltaic power generation system is running in parallel with the oil generator mode, that is, when the first switch circuit is in the closed state and the ATS is in the state of connecting to the oil generator, if the oil generator fails, the third high-level signal indicating the oil generator failure is sent to the inverter. After the inverter receives the oil generator failure signal or determines that the oil generator needs to be stopped based on other conditions (such as the photovoltaic module or energy storage device is restored to the point where it can supply power to the load), the first switch circuit is disconnected, the inverter circuit is controlled to switch to the voltage source mode, and the photovoltaic power generation system switches from the parallel with the oil generator mode to the off-grid mode. Then, the control circuit sends a fourth low-level signal indicating shutdown to the oil generator, and the oil generator performs a shutdown operation according to the fourth low-level signal.

[0086] When the photovoltaic power generation system is running in the oil generator mode, that is, when the first switch circuit is in the closed state, and the state of the ATS is connected to the oil generator, if the ATS detects that the power grid has returned to normal, that is, after the ATS detects that the voltage of the power grid is greater than the threshold, the ATS performs a blanking operation before switching its state to the power grid, that is, the ATS is neither connected to the oil generator nor to the power grid, so that the voltage of the grid-side port is abnormal. When the control circuit detects that the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, the control circuit disconnects the first switch circuit and controls the inverter circuit to switch to the voltage source mode at the same time, and the photovoltaic power generation system switches from the grid-connected mode to the off-grid mode. Afterwards, the ATS switches to connect to the grid, so that the ATS switches to the state of connecting to the grid, and the ATS sends a second low-level signal indicating the connection to the grid to the inverter. When the control circuit detects that the voltage of the grid-side port is greater than the undervoltage protection voltage value, the control circuit closes the first switch circuit and controls the inverter circuit to switch to the current source mode, and the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode.

[0087] When the photovoltaic power generation system is operating in off-grid mode, that is, when the first switch circuit is in the disconnected state, if the ATS detects that the voltage of the grid has returned to normal, the ATS switches to the state of connecting to the grid and sends a second low-level signal indicating the connection to the grid to the inverter. When the control circuit detects that the voltage of the grid-side port is greater than the undervoltage protection voltage value, the control circuit closes the first switch circuit and controls the inverter circuit to switch to the current source mode, and the photovoltaic power generation system switches from the off-grid mode to the grid-connected mode.

[0088] In some embodiments of the present application, when the photovoltaic power generation system switches from an off-grid mode to a grid-connected mode or a diesel generator mode, when the control circuit detects that the voltage of the grid-side port is greater than the undervoltage protection voltage value, in order to ensure the stability of power supply during the switching to the grid-connected mode, it is necessary to first synchronize the voltage of the off-grid port and the voltage of the grid-side port, and close the first switch circuit after the synchronization conditions are met.

[0089] Specifically, when the control circuit detects that the voltage of the grid-side port is greater than the under-voltage protection voltage value, before closing the first switch circuit, it first controls the inverter circuit to switch to the VSG control mode. The inverter circuit adjusts the amplitude and frequency of the output voltage according to the grid-side port voltage information, and can also adjust the phase. After the control circuit detects that the difference in voltage amplitude, phase and frequency between the grid-side port and the off-grid port meets the conditions, it means that the voltage of the grid-side port and the voltage of the off-grid port are synchronized. The control circuit closes the first switch circuit to complete the operation of closing the first switch circuit.

[0090] The above-mentioned photovoltaic power generation system and its control method provided by the present application are used to control the switch circuit of the on-grid and off-grid mode connected between the inverter and the ATS, and the ATS is used to realize switching between the grid side of the switch circuit connected to the power grid or the grid side of the switch circuit connected to the oil generator. When the photovoltaic power generation system is operating in the on-grid mode, if the power grid is abnormal, it switches to the off-grid mode, that is, the photovoltaic module or the energy storage device is used to power the load. When the photovoltaic module or the energy storage device is powering the load, that is, when the photovoltaic power generation system is operating in the off-grid mode, if the photovoltaic module or the energy storage device is insufficiently powered due to certain factors, it switches to the oil-connected generator mode. Through the above-mentioned switching process, the continuous and stable power supply to the load can be achieved when the photovoltaic power generation system switches between different power sources.

[0091] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A photovoltaic power generation system, characterized in that: include: Inverter, on-grid and off-grid controller and automatic transfer switch ATS; The on-grid and off-grid controller comprises: a switch circuit and a control circuit; The DC side of the inverter is used to connect to a photovoltaic module or an energy storage device, and the AC side of the inverter is connected to the inverter side of the switch circuit; The ATS is used to switch between connecting the grid side of the switch circuit to the power grid or connecting the grid side of the switch circuit to the oil generator; The control circuit is used for: When the switch circuit is in a closed state and the ATS is in a state of being connected to the power grid, if the voltage on the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected and the inverter is controlled to switch to a voltage source mode; When the switch circuit is in the disconnected state, if an oil engine start command is received, the oil generator is controlled to run; if the state of the ATS is to connect to the oil generator and the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed and the inverter is controlled to switch to the current source mode.

2. The photovoltaic power generation system according to claim 1, characterized in that: The control circuit is also used for: When the switch circuit is in a closed state and the ATS is connected to the oil generator, if an oil generator stop command is received, the switch circuit is disconnected, the inverter is controlled to switch to a voltage source mode, and the oil generator is controlled to stop.

3. The photovoltaic power generation system according to claim 1 or 2, characterized in that: The control circuit is also used for: When the switch circuit is in a closed state and the ATS is in a state of connecting to the oil generator, if the ATS detects that the voltage of the grid is greater than the undervoltage protection voltage value before switching to the grid side of the switch circuit to connect to the grid, if the voltage of the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected, and the inverter is controlled to switch to the voltage source mode; When the switch circuit is in an open state and the ATS is in a state of being connected to the power grid, if the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed and the inverter is controlled to switch to a current source mode.

4. The photovoltaic power generation system according to any one of claims 1 to 3, characterized in that: The on-grid and off-grid controller comprises: an inverter side port and a grid side port; the inverter side port is connected to the AC side of the inverter, and the grid side port is used to connect to the ATS; The switch circuit comprises: a first relay and a second relay connected in series; the first relay is connected to the inverter side port, and the second relay is connected to the grid side port; The controller is used to close the switch circuit, specifically including: the controller is used to control the inverter to switch to a virtual synchronous generator (VSG) control mode, close the first relay, and close the second relay when the voltage on the inverter side is synchronized with the voltage on the grid side.

5. The photovoltaic power generation system according to any one of claims 1 to 4, characterized in that: It also includes a system controller, wherein the system controller is integrated inside the on-grid and off-grid controller, or the system controller is arranged outside the on-grid and off-grid controller; The system controller is used to send the status of the ATS to the control circuit, indicating that the ATS is connected to the power grid or connected to the oil generator, and send the oil engine start instruction or the oil engine stop instruction to the control circuit.

6. A control method for a photovoltaic power generation system, characterized in that: include: When the switch circuit is in a closed state and the ATS connected to the switch circuit is in a state of being connected to the grid, if the grid-side voltage of the switch circuit is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected and the inverter is controlled to switch to the voltage source mode; When the switch circuit is in the disconnected state, if a diesel engine start command is received, the diesel generator is controlled to run; if the state of the ATS is to be connected to the diesel generator and the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed and the inverter is controlled to switch to the current source mode.

7. The control method according to claim 6, characterized in that: Also includes: When the switch circuit is in a closed state and the ATS is connected to the oil generator, if an oil generator stop command is received, the switch circuit is disconnected, the inverter is controlled to switch to a voltage source mode, and the oil generator is controlled to stop.

8. The control method according to claim 6 or 7, characterized in that: Also includes: When the switch circuit is in a closed state and the ATS is in a state of connecting to the oil generator, if the ATS detects that the voltage of the grid is greater than the undervoltage protection voltage value before switching to the grid side of the switch circuit to connect to the grid, if the voltage of the grid side is less than or equal to the undervoltage protection voltage value, the switch circuit is disconnected, and the inverter is controlled to switch to the voltage source mode; When the switch circuit is in an open state and the ATS is in a state of being connected to the power grid, if the voltage on the grid side is greater than the undervoltage protection voltage value, the switch circuit is closed and the inverter is controlled to switch to a current source mode.

9. The control method according to any one of claims 6 to 8, characterized in that: The closing of the switch circuit specifically includes: The inverter is controlled to switch to a virtual synchronous generator (VSG) control mode, a first relay connected to the AC side of the inverter is closed, and when the voltage on the inverter side is synchronized with the voltage on the grid side, a second relay connected to the ATS is closed.

10. A photovoltaic power generation system, characterized in that: include: Inverter and ATS; the inverter includes: an inverter circuit, a first switch circuit, a grid-side port and a control circuit; The DC side of the inverter circuit is used to connect to a photovoltaic module or an energy storage device, and the first switch circuit is connected between the AC side of the inverter circuit and the grid-side port; The ATS is used to switch between the grid-side port being connected to the power grid or the grid-side port being connected to the oil generator; The control circuit is used for: When the first switch circuit is in a closed state and the ATS is in a state of being connected to the power grid, if the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, the first switch circuit is disconnected, and the inverter circuit is controlled to switch to a voltage source mode; When the first switch circuit is in the disconnected state, the oil generator is controlled to operate; if the state of the ATS is connected to the oil generator and the voltage of the grid-side port is greater than the undervoltage protection voltage value, the first switch circuit is closed and the inverter circuit is controlled to switch to the current source mode.

11. The photovoltaic power generation system according to claim 10, characterized in that: The control circuit is also used for: When the first switch circuit is in a closed state and the ATS is in a state of being connected to the oil generator, the first switch circuit is disconnected, the inverter circuit is controlled to switch to a voltage source mode, and the oil generator is controlled to shut down.

12. The photovoltaic power generation system according to claim 10 or 11, characterized in that: The control circuit is also used for: When the first switch circuit is in a closed state and the state of the ATS is connected to the oil generator, if the ATS detects that the voltage of the grid is greater than a threshold value, before switching to the grid-side port to connect to the grid, if the voltage of the grid-side port is less than or equal to the undervoltage protection voltage value, the first switch circuit is disconnected, and the inverter circuit is controlled to switch to the voltage source mode; When the first switch circuit is in an open state and the ATS is in a state of being connected to the power grid, if the voltage of the grid-side port is greater than the undervoltage protection voltage value, the first switch circuit is closed and the inverter circuit is controlled to switch to a current source mode.

13. The photovoltaic power generation system according to any one of claims 10 to 12, characterized in that: Also includes: An off-grid port and a second switch circuit, wherein the off-grid port is used to connect to a backup power load; The controller is also used to: control the second switch circuit to be in a closed state; The controller is also used to: before closing the first switch circuit, control the inverter circuit to switch to a virtual synchronous generator (VSG) control mode, and close the first switch circuit when the voltage of the off-grid port is synchronized with the voltage of the grid-side port.

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