Power generation system

Abstract

The invention provides a power generation system. The power generation system comprises a power conversion device, a grid-connected and off-grid switching device and an I / O bus. The grid-connected and off-grid switching device is used for being connected between the alternating current end of the power conversion device and a power grid, the grid-connected and off-grid switching device is further used for being connected with a load, and the power conversion device and the grid-connected and off-grid switching device are both connected to the I / O bus. The power conversion device or the grid-connected and off-grid switching device outputs a low-level signal to the I-O bus under the condition that the power grid breaks down, so that the signal on the I-O bus is switched from a high-level signal to the low-level signal. And after the signal on the I / O bus is switched from a high level signal to a low level signal, the power conversion device is switched to a voltage source mode, and the grid-connected and off-grid switching device disconnects the electric connection between the power conversion device and the power grid. By adopting the method and the device, seamless switching can be realized in the process of switching the power conversion device from the grid-connected control mode to the off-grid control mode, and each device can be reliably switched to the off-grid control mode.

Description

Technical Field

[0001] The present application relates to the field of power supply technology, and in particular to a power generation system. Background Art

[0002] The power generation system generally has off-grid support function, on-grid and off-grid switching function and off-grid parallel function. In specific implementation, there are usually two system architectures for power generation systems with on-grid and off-grid functions. One is that the on-grid and off-grid switching device is integrated with the inverter, and the other is that the on-grid and off-grid switching device is separated from the inverter. Regardless of whether the on-grid and off-grid switching device and the inverter are integrated or separated, how the power generation system switches from on-grid operation to off-grid operation is particularly critical.

[0003] Currently, in Figure 1 In the split-type photovoltaic storage power generation system shown, photovoltaic storage inverter 101 to photovoltaic storage inverter 10n, a total of n photovoltaic storage inverters, perform grid abnormality detection and stop output when a grid abnormality is detected. When the on-grid and off-grid switching device detects a grid abnormality, a disconnection signal is sent to the n photovoltaic storage inverters, so that the n photovoltaic storage inverters are uniformly started off-grid.

[0004] In the above scheme, when the photovoltaic storage inverter detects the abnormality of the power grid before the grid-connected and off-grid switching device, it will cause the n photovoltaic storage inverters to be unable to achieve seamless switching (i.e., continuous power supply to the load) during the process of switching from grid-connected operation to off-grid operation. In addition, if the n photovoltaic storage inverters can achieve seamless switching during the process of switching from grid-connected operation to off-grid operation, the photovoltaic storage inverter that first identifies the abnormality of the power grid will switch to off-grid operation, resulting in a situation where the grid-connected operation and off-grid operation are mixed in the n photovoltaic storage inverters and the grid-connected and off-grid switching devices, and then, some of the n photovoltaic storage inverters and the grid-connected and off-grid switching devices cannot identify the abnormality of the power grid and remain in grid-connected operation. Summary of the invention

[0005] The present application provides a power generation system that can not only achieve seamless switching of a power conversion device in the power generation system from a grid-connected control mode to an off-grid control mode, but also enable each device in the power generation system to reliably switch to an off-grid control mode.

[0006] In a first aspect, the present application provides a power generation system, which includes a power conversion device, an on-grid switching device and an IO bus. The DC end of the power conversion device is connected to a DC power supply, the on-grid switching device is connected between the AC end of the power conversion device and the power grid, the on-grid switching device is also connected to a load, and the power conversion device and the on-grid switching device are both connected to the IO bus. Among them, when the AC voltage at the connection point between the on-grid switching device and the power grid is less than a voltage threshold, the power conversion device or the on-grid switching device outputs a low-level signal to the IO bus to switch the signal on the IO bus from a high-level signal to a low-level signal. After the signal on the IO bus is switched from a high-level signal to a low-level signal, the power conversion device switches to a voltage source mode, and the on-grid switching device disconnects the electrical connection between the power conversion device and the power grid.

[0007] In this embodiment, the on-grid switching device or the power conversion device pulls down the high-level signal on the IO bus to a low-level signal when a grid fault is detected. After that, the on-grid switching device and the power conversion device are directly switched to their respective off-grid control modes after the signal on the IO bus is switched from a high-level signal to a low-level signal. Since the power conversion device does not stop output during the process of switching from the grid-connected control mode to the off-grid control mode, it can be ensured that the power conversion device can continuously supply power to the load during the process of switching from the grid-connected control mode to the off-grid control mode, that is, seamless switching can be achieved. In addition, since the on-grid switching device and the power conversion device both switch the off-grid control mode based on the signal change on the IO bus, it can effectively avoid the situation that the device with a slower speed of detecting grid faults cannot detect the grid fault and remains in the grid-connected control mode due to the mixing of the off-grid control mode and the grid-connected control mode in the power conversion device and the on-grid switching device, thereby ensuring that the on-grid switching device and the power conversion device can reliably switch to the off-grid control mode.

[0008] In combination with the first aspect, in a first possible implementation manner, the power conversion device switches to a voltage source mode after a preset time period has passed after a signal on the IO bus switches from a high level signal to a low level signal. The on-grid switching device disconnects the electrical connection between the power conversion device and the grid after a preset time period has passed after a signal on the IO bus switches from a high level signal to a low level signal.

[0009] In this embodiment, after the signal on the IO bus is switched from a high-level signal to a low-level signal, the start time of the off-grid control mode switching of the power conversion device can be aligned with the start time of the off-grid control mode switching of the on-grid and off-grid switching device by delaying for a preset time period, thereby enabling each device to achieve synchronous off-grid control mode switching.

[0010] In combination with the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner, the power conversion device or the grid-connected and off-grid switching device also outputs a low-level signal to the IO bus after the signal on the IO bus is switched from a high-level signal to a low-level signal.

[0011] In this embodiment, the power conversion device or the grid-connected and off-grid switching device that detects grid faults at a slower speed not only switches to the respective off-grid control modes after the signal on the IO bus switches from a high-level signal to a low-level signal, but also outputs a low-level signal to the IO bus to ensure that the signal on the IO bus is reliably pulled down to a low-level signal, thereby improving the reliability of the signal on the IO bus, and further ensuring that the grid-connected and off-grid switching device and the power conversion device can switch to the off-grid control mode more reliably and accurately.

[0012] In combination with any one of the first aspect to the second possible implementation manner of the first aspect, in a third possible implementation manner, each device in the power conversion device and the grid-connected and off-grid switching device includes an IO signal generation circuit and a controller. The controller controls the IO signal generation circuit to output a low level signal to the IO bus when the AC voltage at the connection point between the grid-connected and off-grid switching device and the grid is less than a voltage threshold.

[0013] In combination with the third possible implementation manner of the first aspect, in a fourth possible implementation manner, the IO signal generating circuit includes a resistor and a switch, wherein the resistor and the switch are connected in series between the output end of the auxiliary power supply and the reference ground, and the connection between the resistor and the switch is connected to the output end of the IO signal generating circuit. The controller controls the switch to close when the AC voltage at the connection between the on-grid and off-grid switching device and the power grid is less than the voltage threshold, so that the IO signal generating circuit outputs a low level signal to the IO bus.

[0014] In this embodiment, the IO signal generating circuit is a wired-AND logic circuit, which has a simple structure and is easy to implement.

[0015] In combination with any one of the first aspect to the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner, the grid-connected switching device includes a grid-connected switch connected between the AC end of the power conversion device and the power grid. The grid-connected and off-grid switching device controls the grid-connected switch to disconnect, so as to disconnect the electrical connection between the power conversion device and the power grid.

[0016] In combination with any one of the first aspect to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner, the power generation system includes a plurality of power conversion devices, and the AC ends of the plurality of power conversion devices are connected in parallel.

[0017] In this embodiment, the power generation system is suitable for application scenarios where multiple power conversion devices are connected in parallel.

[0018] In a second aspect, the present application provides a power generation system, which includes a plurality of power conversion devices and an IO bus, wherein the DC end of the power conversion device is connected to a DC power supply, and the AC ends of the plurality of power conversion devices are connected in parallel to a power grid and a load, and the plurality of power conversion devices are all connected to the IO bus. Among them, when the voltage at the AC end of any of the plurality of power conversion devices is less than a voltage threshold, indicating a power grid failure, a low-level signal is output to the IO bus to switch the signal on the IO bus from a high-level signal to a low-level signal. After the signal on the IO bus is switched from a high-level signal to a low-level signal, each power conversion device switches to a voltage source mode and disconnects the electrical connection between the power conversion device and the power grid.

[0019] In this embodiment, any power conversion device with a faster detection speed pulls down the high-level signal on the IO bus to a low-level signal when a power grid fault is detected. After that, each power conversion device directly switches to the off-grid control mode after the signal on the IO bus is switched from a high-level signal to a low-level signal. Since there is no situation of stopping output during the process of switching the power conversion device from the grid-connected control mode to the off-grid control mode, it can be ensured that multiple power conversion devices can achieve seamless switching during the process of switching from the grid-connected control mode to the off-grid control mode. In addition, since each power conversion device switches the off-grid control mode based on the signal change on the IO bus, it can effectively avoid the situation that the device with a slower speed of detecting the grid fault cannot detect the grid fault and remains in the grid-connected control mode due to the mixing of the off-grid control mode and the grid-connected control mode in multiple power conversion devices, thereby ensuring that multiple power conversion devices can reliably switch to the off-grid control mode.

[0020] In combination with the second aspect, in a first possible implementation, the power conversion device switches to a voltage source mode after a preset period of time after the signal on the IO bus switches from a high-level signal to a low-level signal, and disconnects the electrical connection between the power conversion device and the power grid.

[0021] In this embodiment, after the signal on the IO bus is switched from a high-level signal to a low-level signal, the start time of off-grid control mode switching of multiple power conversion devices can be aligned by delaying for a preset period of time, thereby allowing multiple power conversion devices to achieve synchronous off-grid control mode switching.

[0022] In combination with the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner, the power conversion device further outputs a low level signal to the IO bus after the signal on the IO bus is switched from a high level signal to a low level signal.

[0023] In this embodiment, the power conversion device that detects grid faults at a slower speed not only switches to the off-grid control mode after the signal on the IO bus switches from a high-level signal to a low-level signal, but also outputs a low-level signal to the IO bus to ensure that the signal on the IO bus is reliably pulled down to a low-level signal, thereby improving the reliability of the signal on the IO bus, and further ensuring that multiple power conversion devices can switch to the off-grid control mode more reliably and accurately.

[0024] In combination with any one of the second aspect to the second possible implementation manner of the second aspect, in a third possible implementation manner, the power conversion device includes an IO signal generation circuit and a controller. The controller controls the IO signal generation circuit to output a low level signal to the IO bus when the AC terminal voltage of the power conversion device is less than a voltage threshold.

[0025] In combination with the third possible implementation manner of the second aspect, in a fourth possible implementation manner, the IO signal generation circuit includes a resistor and a switch, wherein the resistor and the switch are connected in series between the output end of the auxiliary power supply and the reference ground, and the connection between the resistor and the switch is connected to the output end of the IO signal generation circuit. The controller controls the switch to close when the AC end voltage of the power conversion device is less than the voltage threshold, so that the IO signal generation circuit outputs a low level signal to the IO bus.

[0026] In this embodiment, the IO signal generating circuit is a wired-AND logic circuit, which has a simple structure and is easy to implement.

[0027] In combination with any one of the second aspect to the fourth possible implementation of the second aspect, in a fifth possible implementation, the power conversion device includes a power conversion circuit, a grid-connected switch and an off-grid switch, and the AC end of the power conversion device includes a grid-connected AC end and an off-grid AC end. The grid-connected AC ends of multiple power conversion devices are connected in parallel to the power grid, and the off-grid AC ends of multiple power conversion devices are connected in parallel to the load. The AC end of the power conversion circuit is connected to the grid-connected AC end through the grid-connected switch, and the AC end of the power conversion circuit is also connected to the off-grid AC end through the off-grid switch. The power conversion device controls the grid-connected switch to disconnect to disconnect the electrical connection between the power conversion device and the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of a split photovoltaic storage power generation system provided by the prior art;

[0029] Figure 2 It is a schematic diagram of an application scenario of the power generation system provided by this application;

[0030] Figure 3 It is a structural schematic diagram of a power generation system provided by the present application;

[0031] Figure 4 is another structural schematic diagram of the power generation system provided by the present application;

[0032] Figure 5 It is a structural schematic diagram of the IO signal generating circuit provided by the present application;

[0033] Figure 6 is another structural schematic diagram of the power generation system provided by the present application;

[0034] Figure 7 This is another structural schematic diagram of the power generation system provided by the present application. DETAILED DESCRIPTION

[0035] The power generation system provided in this application can be applied to various application fields such as photovoltaic power generation, energy storage power generation, photovoltaic storage power generation, new energy intelligent microgrid, power transmission and distribution, etc. The power conversion device provided in this application can be an inverter, a power storage converter (Power Convers ion System, PCS), an uninterruptible power supply (Uninterrupted Power Supply, UPS), etc., which are applicable to different application scenarios, such as photovoltaic power generation scenarios, energy storage power generation scenarios, photovoltaic storage hybrid power generation scenarios, UPS power generation scenarios, etc. The following is an example of photovoltaic storage hybrid power generation scenario.

[0036] See also Figure 2 , Figure 2 This is a schematic diagram of the application scenario of the power generation system provided by this application. In the photovoltaic storage hybrid power generation scenario, the power generation system provided by this application is Figure 2 The photovoltaic power generation system shown in the present application comprises a plurality of power conversion devices. Figure 2 The inverters 11a1, ..., and 11a shown in FIG. n The on-grid and off-grid switching device provided in this application is Figure 2 The grid-connected and off-grid controller shown. The photovoltaic power generation system includes inverters 11a1, ..., inverters 11a n , grid-connected and off-grid controller and IO bus, n is an integer greater than or equal to 1. The DC terminals of the n inverters are connected to the photovoltaic strings and battery clusters. The grid-connected and off-grid controller is used to connect between the AC terminal AC111 of the inverter 11a1 and the power grid, ..., and is also connected to the inverter 11a n Between the AC terminal AC11n and the power grid. Here, Figure 2The AC terminals of each inverter are simply drawn, and the AC terminals of each inverter are not specifically drawn. For example, when the inverter is a single-phase inverter, the AC terminals of the inverter include the live terminal and the neutral terminal; when the inverter is a three-phase inverter, the AC terminals of the inverter include the a-phase AC terminal, the b-phase AC terminal, and the c-phase AC terminal. When n is greater than 1, the AC terminals AC111, ..., AC1 ... n The AC terminal AC11n of the inverter 11a1 is connected in parallel. The on-grid controller is also used to connect the load. The IO signal terminal IO111 of the inverter 11a1, ..., the inverter 11a n The IO signal terminal IO11n of the grid-connected and off-grid controller and the IO signal terminal IO21 of the grid-connected and off-grid controller are both connected to the IO bus.

[0037] After the grid-connected switch in the grid-connected and off-grid controller is closed, the n inverters are connected to the grid for operation, that is, each of the n inverters converts the DC power output by the photovoltaic string and the battery cluster into AC power and outputs it to the grid to realize power supply to the grid. In the process of the photovoltaic power generation system supplying power to the grid, the n inverters and the grid-connected and off-grid controller detect whether the AC voltage at the connection between the grid-connected and off-grid controller and the grid is less than the voltage threshold (that is, whether the grid is faulty), and whether the signal on the IO bus is switched from a high-level signal to a low-level signal. In the case that any device among the n inverters and the grid-connected and off-grid controller detects that a grid fault occurs, the IO signal end of the n inverters and the grid-connected and off-grid controller controls itself to output a low-level signal to the IO bus, so that the signal on the IO bus is switched from a high-level signal to a low-level signal. After the signal on the IO bus is switched from a high-level signal to a low-level signal, each inverter switches to the off-grid control mode of the inverter, that is, the voltage source mode, and the grid-connected and off-grid controller switches to the off-grid control mode of the grid-connected and off-grid controller, that is, the electrical connection between each inverter and the grid is disconnected. Then, the photovoltaic power generation system realizes power supply to the load.

[0038] It can be understood that any device that detects grid faults faster among the n inverters and the on-grid and off-grid controllers pulls down the high-level signal on the IO bus to a low-level signal when a grid fault is detected. After that, the n inverters and the on-grid and off-grid controllers are directly switched to their respective off-grid control modes after the signal on the IO bus is switched from a high-level signal to a low-level signal. Since there is no situation of stopping output during the process of the n inverters switching from the on-grid control mode to the off-grid control mode, it can be ensured that the n inverters can achieve seamless switching during the process of switching from the on-grid control mode to the off-grid control mode. In addition, since the n inverters and the on-grid and off-grid controllers switch the off-grid control mode based on the signal change on the IO bus, it can effectively avoid the situation that the device with a slower speed of detecting grid faults cannot detect the grid fault and remains in the on-grid control mode due to the mixing of the off-grid control mode and the on-grid control mode among the n inverters and the on-grid and off-grid controllers, thereby ensuring that the n inverters and the on-grid and off-grid controllers can reliably switch to the off-grid control mode.

[0039] The above is only an example of the application scenarios of the power generation system provided by the present application, and is not an exhaustive list. The present application does not limit the application scenarios.

[0040] Combine the following Figures 3 to 7 The working principle of the power generation system provided in this application is illustrated by way of example.

[0041] See also Figure 3 , Figure 3 Schematic diagram of a power generation system provided by this application. Figure 3 As shown, the power generation system 1 includes power conversion devices 11, ..., power conversion devices 1n, an on-grid switching device 2 and an IO bus, where n is an integer greater than or equal to 1. Among them, the DC terminal DC11, ... of the power conversion device 11 and the DC terminal DC1n of the power conversion device 1n are all used to connect a DC power source, and the DC power source includes a photovoltaic string, a battery cluster, etc. The on-grid switching device 2 is used to connect between the AC terminal AC11 of the power conversion device 11 and the power grid, ..., and is also connected between the AC terminal AC1n of the power conversion device 1n and the power grid. When n is greater than 1, the AC terminals AC11, ... of the power conversion device 11 and the AC terminal AC1n of the power conversion device 1n are connected in parallel. Here, Figure 3The DC end and AC end of each power conversion device in the figure are simplified, and the DC end and AC end of each power conversion device are not specifically expanded to draw. In fact, the DC end of each power conversion device usually includes a positive DC end and a negative DC end. When the power conversion device is a single-phase power conversion device, the AC end AC11 of the power conversion device 11 includes a live wire end AC11L and a neutral wire end AC11N; when the power conversion device is a three-phase power conversion device, the AC end AC11 of the power conversion device 11 includes three-phase AC ends AC11a, AC11b and AC11c. The grid-connected switching device 2 is also used to connect the load. The power conversion devices 11, ..., the power conversion device 1n and the grid-connected switching device 2 are all connected to the IO bus. Specifically, the IO signal end IO11 of the power conversion device 11, ..., the IO signal end IO1n of the power conversion device 1n and the IO signal end of the grid-connected switching device 2 are all connected to the IO bus. Exemplarily, the IO signal end is a digital signal input DI / digital signal output DO interface.

[0042] In one embodiment, when the AC voltage at the connection point between the on-grid and off-grid switching device and the power grid is less than the voltage threshold, any one of the n power conversion devices and the on-grid and off-grid switching device 2 indicates that a fault has occurred in the power grid, and a low-level signal is output to the IO bus to switch the signal on the IO bus from a high-level signal to a low-level signal. After the signal on the IO bus is switched from a high-level signal to a low-level signal, each power conversion device switches to a voltage source mode, and the on-grid and off-grid switching device 2 disconnects the electrical connection between each power conversion device and the power grid.

[0043] For details, please refer to Figure 4 , Figure 4 is another structural schematic diagram of the power generation system provided by the present application. Figure 4As shown, the power conversion device 11 includes a power conversion circuit 111, an IO signal generating circuit 112 and a controller 113, the DC end of the power conversion circuit 111 is respectively connected to the DC end DC11+ and the DC end DC11- of the power conversion device 11, the AC end of the power conversion circuit 111 is connected to the AC end AC11 of the power conversion device 11, and the output end of the IO signal generating circuit 112 is connected to the IO signal end of the power conversion device 11; ...; the power conversion device 1n includes a power conversion circuit 1n1, an IO signal generating circuit 1n2 and a controller 1n3, the DC end of the power conversion circuit 1n1 is respectively connected to the DC end DC1n+ and the DC1n- of the power conversion device 1n, the AC end of the power conversion circuit 1n1 is connected to the AC end AC1n of the power conversion device 1n, and the output end of the IO signal generating circuit 1n2 is connected to the IO signal end of the power conversion device 1n. The on-grid switching device 2 includes a grid-connected switch S1, an IO signal generating circuit 21 and a controller 22. The grid-connected switch S1 is connected between the AC terminal AC11 of the power conversion device 11 and the power grid, ..., and is also connected between the AC terminal AC1n of the power conversion device 1n and the power grid. The connection between the AC terminal AC11 of the power conversion device 11, ..., the AC terminal AC1n of the power conversion device 1n and the grid-connected switch S1 is used to connect the load. The output end of the IO signal generating circuit 21 is connected to the IO signal end of the grid-connected and off-grid switching device 2.

[0044] Since the IO signal generating circuits in the n power conversion devices and the on-grid switching device 2 are the same, for ease of description, the IO signal generating circuit 112 is taken as an example for description. Figure 5 , Figure 5 Schematic diagram of the structure of the IO signal generation circuit provided by this application. Figure 5 As shown, the IO signal generating circuit 112 includes a resistor R and a switch Q, which are connected in series between the output terminal Vcc of the auxiliary power supply and the reference ground GND, and the connection between the resistor R and the switch Q is connected to the output terminal o112 of the IO signal generating circuit 112. The auxiliary power supply is used to supply power to the controller 113 and the IO signal generating circuit 112.

[0045] Specifically, when the power generation system 1 is in grid-connected operation, the n power conversion devices and the grid-connected and off-grid switching device 2 are all in their respective grid-connected control modes, that is, the controller 22 controls the grid-connected switch S1 to be in a closed state, the controller 113 controls the power conversion circuit 111 to be in a current source mode, ..., the controller 1n3 controls the power conversion circuit 1n1 to be in a current source mode, so as to realize power supply to the grid and the load. In addition, when the power generation system 1 is in grid-connected operation, each of the n power conversion devices and the grid-connected and off-grid switching device 2 controls its own IO signal generation circuit to output a high-level signal, for example, the switch Q of the IO signal generation circuit in each device is controlled to be disconnected, so that the IO signal end of each device outputs a high-level signal, so that the signal on the IO bus is a high-level signal.

[0046] When the power generation system 1 supplies power to the grid and the load, the controllers of each device detect in real time whether a fault occurs in the grid and whether the signal on the IO bus switches from a high-level signal to a low-level signal.

[0047] The way in which each device detects whether a fault occurs in the power grid is as follows: the controller of each power conversion device, when detecting that the AC voltage at the AC end of the device in which it is located is less than the voltage threshold, indicates that the AC voltage at the connection between the on-grid and off-grid switching device 2 and the power grid is less than the voltage threshold, determines that a fault occurs in the power grid; the controller 22 of the on-grid and off-grid switching device 2, when detecting that the AC voltage at the connection between the on-grid and off-grid switching device 2 and the power grid is less than the voltage threshold, determines that a fault occurs in the power grid. Exemplarily, the voltage threshold may be 70%-80% of the rated voltage of the power grid.

[0048] In fact, the speeds at which the n power conversion devices and the grid-connected and off-grid switching device 2 detect grid faults are different. Any device with a faster detection speed among the n power conversion devices and the grid-connected and off-grid switching device 2, when detecting a grid fault, controls the IO signal generation circuit in the power conversion device where it is located to output a low-level signal, for example, controls the switch Q in the IO signal generation circuit to be closed, so as to output a low-level signal to the IO bus, thereby switching the signal on the IO bus from a high-level signal to a low-level signal. Afterwards, the controller of each power conversion device, when detecting that the signal on the IO bus is switched from a high-level signal to a low-level signal, controls the power conversion device where it is located to switch from the grid-connected control mode to the off-grid control mode, that is, from the current source mode to the voltage source mode; the controller 22 of the grid-connected and off-grid switching device 2, when detecting that the signal on the IO bus is switched from a high-level signal to a low-level signal, controls the grid-connected and off-grid switching device 2 to switch to the off-grid control mode, that is, controls the grid-connected switch S1 to be disconnected, so as to disconnect the electrical connection between the n power conversion devices and the grid.

[0049] When any of the n power conversion devices and the on-grid and off-grid switching device 2 outputs a low-level signal to the IO bus, the signal on the IO bus will be switched from a high-level signal to a low-level signal.

[0050] It can be understood that some of the n power conversion devices and the on-grid and off-grid switching devices 2 that first detect the grid fault directly pull down the high-level signal on the IO bus to a low-level signal. The n power conversion devices and the on-grid and off-grid switching devices 2 are switched from their respective on-grid control modes to their respective off-grid control modes when the signal on the IO bus is switched from a high-level signal to a low-level signal. Since there is no situation of stopping output during the process of the n power conversion devices switching from the on-grid control mode to the off-grid control mode, it can be ensured that the n power conversion devices can achieve seamless switching during the process of switching from the on-grid control mode to the off-grid control mode. In addition, since the n power conversion devices and the on-grid and off-grid switching devices 2 are all based on the signal changes on the IO bus to switch the off-grid control mode, it can effectively avoid the situation that the device with a slower detection speed cannot detect the grid fault and remains in the on-grid control mode due to the mixing of the on-grid control mode and the off-grid control mode in the n power conversion devices and the on-grid and off-grid switching devices 2, thereby ensuring that the n power conversion devices and the on-grid and off-grid switching devices 2 can be reliably switched to the off-grid control mode.

[0051] Furthermore, compared to the above-mentioned embodiment of switching the power generation system 1 between the grid-connected and off-grid control modes, the device for detecting grid faults at a slower speed in this embodiment, when detecting that the signal on the IO bus switches from a high-level signal to a low-level signal, not only switches from the grid-connected control mode to the off-grid control mode, but also outputs a low-level signal to the IO bus, so that each device outputs a low-level signal to the IO bus to ensure that the signal on the IO bus is reliably pulled down to a low-level signal, thereby improving the reliability of the signal on the IO bus, and further ensuring that the n power conversion devices and the grid-connected and off-grid switching device 2 can switch to the off-grid control mode more reliably and accurately.

[0052] It should be noted that when the power conversion device or the grid-connected / off-grid switching device 2 both outputs a low-level signal and switches to an off-grid control mode, the present application does not limit the order in which the power conversion device or the grid-connected / off-grid switching device 2 outputs a low-level signal and switches to an off-grid control mode.

[0053] Exemplarily, the device that first detects the grid fault among the n power conversion devices and the on-grid and off-grid switching devices 2 can output a low-level signal to the IO bus and switch to the off-grid control mode at the same time; or, first switch to the off-grid control mode and then output a low-level signal to the IO bus. The other devices among the n power conversion devices and the on-grid and off-grid switching devices 2, except for the device that first detects the grid fault, switch to the off-grid control mode and output a low-level signal to the IO bus when detecting that the signal on the IO bus switches from a high-level signal to a low-level signal; or, first switch to the off-grid control mode and then output a low-level signal to the IO bus. Since what is transmitted on the IO bus in the present application is high-level signals and low-level signals, it belongs to hardware communication and is faster than protocol communication. Therefore, even if the device that detects the grid fault first directly switches to the off-grid control mode due to the grid fault and then outputs a low-level signal, other devices except the device that detects the grid fault first directly switch to the off-grid control mode due to the signal on the IO bus switching from a high-level signal to a low-level signal, and the time interval between the switching moments of any two devices among the n power conversion devices and the on-grid and off-grid switching devices 2 is also basically very small and can be ignored, so that the n power conversion devices and the on-grid and off-grid switching devices 2 can basically achieve synchronous off-grid control mode switching.

[0054] Preferably, compared with the previous embodiment, in this embodiment, each device in the n power conversion devices and the grid-connected and off-grid switching device 2 switches to its own off-grid control mode after a preset time period after the signal on the IO bus switches from a high-level signal to a low-level signal, so as to shorten the time interval between the switching moments of any two devices in the n power conversion devices and the grid-connected and off-grid switching device 2, wherein the switching moment of the power conversion device is the moment when the power conversion device switches to the voltage source mode, and the switching moment of the grid-connected and off-grid switching device 2 is the moment when the grid-connected and off-grid switching device 2 disconnects the electrical connection between each power conversion device and the grid, that is, the moment when the grid-connected switch S1 is disconnected. Furthermore, after the signal on the IO bus switches from a high-level signal to a low-level signal, the start time of the off-grid control mode switching of the n power conversion devices and the grid-connected and off-grid switching device 2 can be aligned by delaying the preset time period, so that the n power conversion devices and the grid-connected and off-grid switching device 2 can achieve synchronous off-grid control mode switching.

[0055] Optionally, the on-grid and off-grid switching device 2 further includes an off-grid switch S2, which is used to be connected between the AC terminal AC11 of the power conversion device 11 and the load, ..., and also connected between the AC terminal AC1n of the power conversion device 1n and the load. Figure 4 The embodiment of switching the on-grid and off-grid control mode of the power generation system 1 shown in the figure is also applicable to the power generation system in which the on-grid and off-grid switching device 2 also includes an off-grid switch S2. Figure 4The grid-connected control mode of the grid-connected and off-grid switching device 2 in the illustrated embodiment is modified from controlling the grid-connected switch S1 to be closed to controlling both the grid-connected switch S1 and the off-grid switch S2 to be closed.

[0056] In the present application, some devices of the n power conversion devices and the on-grid and off-grid switching devices 2 that first detect the grid fault directly pull down the high-level signal on the IO bus to a low-level signal. The n power conversion devices and the on-grid and off-grid switching devices 2 are switched from their respective on-grid control modes to their respective off-grid control modes when the signal on the IO bus is switched from a high-level signal to a low-level signal. Since there is no situation of stopping output during the process of the n power conversion devices switching from the on-grid control mode to the off-grid control mode, it can be ensured that the n power conversion devices can achieve seamless switching during the process of switching from the on-grid control mode to the off-grid control mode. In addition, since the n power conversion devices and the on-grid and off-grid switching devices 2 are all based on the signal changes on the IO bus to switch the off-grid control mode, it can effectively avoid the situation that the device with a slower detection speed cannot detect the grid fault and remains in the on-grid control mode due to the mixing of the off-grid control mode and the on-grid control mode in the n power conversion devices and the on-grid and off-grid switching devices 2, so that the n power conversion devices and the on-grid and off-grid switching devices 2 can be reliably switched to the off-grid control mode.

[0057] See also Figure 6 , Figure 6 is another structural schematic diagram of the power generation system provided by the present application. Figure 6 As shown, the power generation system 1 includes power conversion devices 11, ..., power conversion devices 1n and an IO bus, where n is an integer greater than 1. The AC terminals AC11, ..., AC terminals AC1n of the power conversion devices 11 and AC1n of the power conversion devices 1n are connected in parallel to connect the power grid and the load. For the specific connection relationship of the other parts of the power generation system 1 except the AC terminals of the n power conversion devices, please refer to Figure 3 Description of corresponding parts in the power generation system 1 shown.

[0058] In one embodiment, when the voltage at the AC end of any of the n power conversion devices is less than a voltage threshold, indicating that a power grid failure occurs, a low-level signal is output to the IO bus to switch the signal on the IO bus from a high-level signal to a low-level signal. After the signal on the IO bus switches from a high-level signal to a low-level signal, each power conversion device switches to a voltage source mode and disconnects the electrical connection between itself and the power grid.

[0059] For details, please refer to Figure 7 , Figure 7 is another structural schematic diagram of the power generation system provided by the present application. Figure 7As shown, the power conversion device 11 includes a power conversion circuit 111, an IO signal generating circuit 112, a grid-connected switch S11, an off-grid switch S12 and a controller 113. The AC end AC11 of the power conversion device 11 includes a grid-connected AC end AC11_on and an off-grid AC end AC11_off. The AC end of the power conversion circuit 111 is connected to the grid-connected AC end AC11_on of the power conversion device 11 through the grid-connected switch S11. The AC end of the power conversion circuit 111 is also connected to the off-grid AC end AC11_off of the power conversion device 11 through the off-grid switch S12. ...; the power conversion device 1n includes a power conversion circuit 1n1, an IO signal generating circuit 1n2, a grid-connected switch Sn1, an off-grid switch Sn2 and a controller 1n3. The AC end AC1n of the power conversion device 1n includes a grid-connected AC end AC1n_on and an off-grid AC end AC1n_off. The AC end of the power conversion circuit 1n1 is connected to the grid-connected AC end AC11_on of the power conversion device 1n through the grid-connected switch Sn1. n_on, the AC end of the power conversion circuit 1n1 is also connected to the off-grid AC end AC1 of the power conversion device 1n through the off-grid switch Sn2 n_off. Here, for the specific connection relationship of the other parts of each power conversion device except the grid-connected switch and the off-grid switch, please refer to Figure 4 Description of corresponding parts in the power generation system 1 shown.

[0060] Specifically, when the power generation system 1 is connected to the grid, the n power conversion devices are all in the grid control mode, that is, each power conversion device controls its own grid switch and off-grid switch to be closed, and controls its own power conversion circuit to be in the current source mode to realize power supply to the grid and the load. In addition, when the power generation system 1 is connected to the grid, each power conversion device controls its own IO signal generation circuit to output a high-level signal, so that the IO signal end of each power conversion device outputs a high-level signal, so that the signal on the IO bus is a high-level signal.

[0061] In the process of the power generation system 1 supplying power to the grid and the load, the controller of each power conversion device detects in real time whether a fault occurs in the grid, and detects whether the signal on the IO bus switches from a high-level signal to a low-level signal. The way in which the power conversion device detects whether a fault occurs in the grid is as follows: the controller of each power conversion device determines that a fault occurs in the grid when a fault is detected in the grid.

[0062] In fact, the speeds at which n power conversion devices detect grid faults are different. Any device with a fast detection speed among the n power conversion devices, when detecting a grid fault, controls the IO signal generation circuit in its own device to output a low-level signal, so that the signal on the IO bus switches from a high-level signal to a low-level signal. Afterwards, when the controller of each power conversion device detects that the signal on the IO bus switches from a high-level signal to a low-level signal, controls the device in which it is located to switch from a grid-connected control mode to an off-grid control mode, that is, controls the power conversion circuit in its own device to switch from a current source mode to a voltage source mode, and controls the grid-connected switch in its own device to disconnect.

[0063] It can be understood that some of the n power conversion devices that first detect the power grid fault directly pull down the high-level signal on the IO bus to a low-level signal. The n power conversion devices are switched from their respective grid-connected control modes to their respective off-grid control modes when the signal on the IO bus is switched from a high-level signal to a low-level signal. Since there is no situation of stopping output during the process of the n power conversion devices switching from the grid-connected control mode to the off-grid control mode, it can be ensured that the n power conversion devices can achieve seamless switching during the process of switching from the grid-connected control mode to the off-grid control mode. In addition, since the n power conversion devices are all switched to the off-grid control mode based on the signal change on the IO bus, it can effectively avoid the situation that the device with a slower detection speed cannot detect the grid fault and remains in the grid-connected control mode due to the mixing of the grid-connected control mode and the off-grid control mode in the n power conversion devices, thereby ensuring that the n power conversion devices can be reliably switched to the off-grid control mode.

[0064] Furthermore, compared to the above-mentioned embodiment of switching the power generation system 1 between the grid-connected and off-grid control modes, the device for detecting grid faults at a slower speed in this embodiment, when detecting that the signal on the IO bus switches from a high-level signal to a low-level signal, not only switches from the grid-connected control mode to the off-grid control mode, but also outputs a low-level signal to the IO bus, so that each power conversion device outputs a low-level signal to the IO bus, to ensure that the signal on the IO bus is reliably pulled down to a low-level signal, thereby improving the reliability of the signal on the IO bus, and further ensuring that n power conversion devices can switch to the off-grid control mode more reliably and accurately.

[0065] It should be noted that when the power conversion device executes both outputting a low-level signal and switching to an off-grid control mode, the present application does not limit the order in which the power conversion device executes outputting a low-level signal and switching to an off-grid control mode.

[0066] Exemplarily, the device that detects the grid fault first among the n power conversion devices can output a low-level signal to the IO bus and switch to the off-grid control mode at the same time; or, it can first switch to the off-grid control mode and then output a low-level signal to the IO bus. The other devices among the n power conversion devices, except the device that detects the grid fault first, switch to the off-grid control mode and output a low-level signal to the IO bus when detecting that the signal on the IO bus switches from a high-level signal to a low-level signal; or, it can first switch to the off-grid control mode and then output a low-level signal to the IO bus. Since what is transmitted on the IO bus in the present application is a high-level signal and a low-level signal, it belongs to hardware communication and is faster than protocol communication. Therefore, even if the device that detects the grid fault first directly switches to the off-grid control mode due to the grid fault and then outputs a low-level signal, other devices except the device that detects the grid fault first directly switch to the off-grid control mode due to the signal on the IO bus switching from a high-level signal to a low-level signal. The time interval between the switching moments of any two devices among the n power conversion devices is also basically very small and can be ignored, so that the n power conversion devices can basically achieve synchronous off-grid control mode switching.

[0067] Preferably, compared with the previous embodiment, in this embodiment, each power conversion device switches to the off-grid control mode after a preset time period after the signal on the IO bus switches from a high-level signal to a low-level signal, so as to shorten the time interval between the switching moments of any two devices among the n power conversion devices. Furthermore, the start time of the off-grid control mode switching of the n power conversion devices can be aligned by delaying the preset time period after the signal on the IO bus switches from a high-level signal to a low-level signal, so that the n power conversion devices can achieve synchronous off-grid control mode switching.

[0068] Optional, Figure 7 The grid-connected control mode of the power conversion device in the power generation system 1 shown can also be to control its own grid-connected switch to be closed, and to control its own power conversion circuit to be in current source mode. Correspondingly, the off-grid control mode of the power conversion device can also be to control its own grid-connected switch to be disconnected, to control its own off-grid switch to be closed, and to control its own power conversion circuit to be in voltage source mode.

[0069] Here, for the specific implementation method of switching the power generation system 1 from the grid-connected control mode to the off-grid control mode, please refer to Figure 4 The description of the corresponding parts in the power generation system 1 shown will not be repeated here.

[0070] In the present application, some devices among the n power conversion devices that first detect the power grid fault directly pull down the high-level signal on the IO bus to a low-level signal. The n power conversion devices are all switched from the grid-connected control mode to the off-grid control mode when the signal on the IO bus is switched from the high-level signal to the low-level signal. Since there is no situation of stopping output during the process of the n power conversion devices switching from the grid-connected control mode to the off-grid control mode, it can be ensured that the n power conversion devices can achieve seamless switching during the process of switching from the grid-connected control mode to the off-grid control mode. In addition, since the n power conversion devices are all switched to the off-grid control mode based on the signal change on the IO bus, it can effectively avoid the situation that the device with a slower detection speed cannot detect the grid fault and remains in the grid-connected control mode due to the mixing of the off-grid control mode and the grid-connected control mode in the n power conversion devices, thereby enabling the n power conversion devices to reliably switch to the off-grid control mode.

[0071] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the 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 power generation system, It is characterized in that The power generation system comprises a power conversion device, an on-grid and off-grid switching device and an IO bus, wherein the DC end of the power conversion device is used to connect a DC power supply, the on-grid and off-grid switching device is used to connect between the AC end of the power conversion device and the power grid, the on-grid and off-grid switching device is also used to connect a load, and the power conversion device and the on-grid and off-grid switching device are both connected to the IO bus, wherein: The power conversion device or the on-grid switching device, when the AC voltage at the connection point between the on-grid switching device and the power grid is less than a voltage threshold, outputs a low-level signal to the IO bus, so that the signal on the IO bus is switched from a high-level signal to the low-level signal; After the signal on the IO bus is switched from the high-level signal to the low-level signal, the power conversion device is switched to the voltage source mode, and the on-grid and off-grid switching device disconnects the electrical connection between the power conversion device and the grid.

2. The power generation system according to claim 1, It is characterized in that The power conversion device switches to the voltage source mode after a preset time period after the signal on the IO bus switches from the high level signal to the low level signal; The on-grid and off-grid switching device disconnects the electrical connection between the power conversion device and the power grid after the preset time period has passed after the signal on the IO bus is switched from the high-level signal to the low-level signal.

3. The power generation system according to claim 1 or 2, It is characterized in that The power conversion device or the on-grid and off-grid switching device further outputs the low-level signal to the IO bus after the signal on the IO bus is switched from the high-level signal to the low-level signal.

4. The power generation system according to any one of claims 1 to 3, It is characterized in that Each device in the power conversion device and the on-grid and off-grid switching device includes an IO signal generating circuit and a controller; The controller controls the IO signal generating circuit to output the low level signal to the IO bus when the AC voltage at the connection point between the on-grid and off-grid switching device and the power grid is less than the voltage threshold.

5. The power generation system according to claim 4, It is characterized in that The IO signal generating circuit comprises a resistor and a switch, wherein the resistor and the switch are connected in series between the output end of the auxiliary power supply and the reference ground, and the connection between the resistor and the switch is connected to the output end of the IO signal generating circuit; The controller controls the switch to close when the AC voltage at the connection point between the on-grid and off-grid switching device and the power grid is less than the voltage threshold, so that the IO signal generating circuit outputs the low level signal to the IO bus.

6. The power generation system according to any one of claims 1 to 5, It is characterized in that The grid-connected switching device comprises a grid-connected switch, and the grid-connected switch is used to be connected between the AC end of the power conversion device and the power grid; The on-grid and off-grid switching device controls the on-grid switch to be disconnected so as to disconnect the electrical connection between the power conversion device and the power grid.

7. The power generation system according to any one of claims 1 to 6, It is characterized in that The power generation system includes a plurality of the power conversion devices, and the AC ends of the plurality of the power conversion devices are connected in parallel.

8. A power generation system, It is characterized in that The power generation system includes a plurality of power conversion devices and an IO bus, wherein the DC end of the power conversion device is used to connect to a DC power supply, and the AC ends of the plurality of power conversion devices are connected in parallel to connect to a power grid and a load, and the plurality of power conversion devices are all connected to the IO bus, wherein: Any power conversion device among the plurality of power conversion devices, when the voltage at the AC end of the power conversion device is less than the voltage threshold, outputs a low level signal to the IO bus, so that the signal on the IO bus is switched from a high level signal to the low level signal; The power conversion device switches to a voltage source mode after the signal on the IO bus switches from the high level signal to the low level signal, and disconnects the electrical connection between the power conversion device and the power grid.

9. The power generation system according to claim 8, It is characterized in that The power conversion device switches to the voltage source mode after a preset time period after the signal on the IO bus switches from the high level signal to the low level signal, and disconnects the electrical connection between the power conversion device and the power grid.

10. The power generation system according to claim 8 or 9, It is characterized in that The power conversion device further outputs the low-level signal to the IO bus after the signal on the IO bus is switched from the high-level signal to the low-level signal.

11. The power generation system according to any one of claims 8 to 10, It is characterized in that The power conversion device includes an IO signal generating circuit and a controller; The controller controls the IO signal generating circuit to output the low level signal to the IO bus when the AC terminal voltage of the power conversion device is less than the voltage threshold.

12. The power generation system according to claim 11, It is characterized in that The IO signal generating circuit comprises a resistor and a switch, wherein the resistor and the switch are connected in series between the output end of the auxiliary power supply and the reference ground, and the connection between the resistor and the switch is connected to the output end of the IO signal generating circuit; The controller controls the switch to close when the AC terminal voltage of the power conversion device is less than the voltage threshold, so that the IO signal generation circuit outputs the low level signal to the IO bus.

13. The power generation system according to any one of claims 8 to 12, It is characterized in that The power conversion device comprises a power conversion circuit, a grid-connected switch and an off-grid switch, and the AC end of the power conversion device comprises a grid-connected AC end and an off-grid AC end; The grid-connected AC ends of the plurality of power conversion devices are connected in parallel for connecting to the grid, and the off-grid AC ends of the plurality of power conversion devices are connected in parallel for connecting to the load; The AC end of the power conversion circuit is connected to the grid-connected AC end through the grid-connected switch, and the AC end of the power conversion circuit is also connected to the off-grid AC end through the off-grid switch; The power conversion device controls the grid-connected switch to be disconnected so as to disconnect the electrical connection between the power conversion device and the power grid.

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