Fault detection device and method and grid-connected photovoltaic power generation system

Abstract

The invention provides a fault detection device and method and a grid-connected photovoltaic power generation system, which are used for improving the failure detection accuracy of a filter capacitor and ensuring the stable operation of the grid-connected photovoltaic power generation system. The fault detection device comprises a temperature detection unit, a current detection unit, a controller and a breaking unit. The temperature detection unit is coupled with the plurality of filter capacitors between the output end of the grid-connected inverter and the power grid, and is used for detecting the temperature of the plurality of filter capacitors and outputting the temperature to the controller; the current detection unit is coupled with the plurality of filter capacitors and is used for detecting the current of the plurality of filter capacitors and outputting the current to the controller; the controller is connected with the temperature detection unit, the current detection unit and the breaking unit and used for controlling the breaking unit to be disconnected when the received temperature exceeds a first threshold value and the received current exceeds a second threshold value. And the breaking unit is connected between the output end of the grid-connected inverter and the plurality of filter capacitors and is used for being opened or closed under the control of the controller.

Description

[0001] This application is a divisional application. The original application has the application number 202110199883.3 and the original application date is February 22, 2021. The entire contents of the original application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of photovoltaic power generation, and more particularly to a fault detection device, method and grid-connected photovoltaic power generation system. Background Technology

[0003] With increasing societal focus on energy, power generation technologies are being applied more and more widely. In practical applications, various types of power generation systems, such as wind turbines, photovoltaic panels, and fuel cells, all need to be connected to the power grid via grid-connected inverters to transmit power to the AC grid.

[0004] The output of a grid-connected inverter is connected to the power grid. The connection point between the grid-connected inverter and the power grid can be called the point of common coupling (PCC) or the grid connection point. A grid-connected inverter can be used to convert the DC power received at the input terminal into AC power required by the power grid, and then transmit it to the power grid through the grid connection point.

[0005] The AC output of a grid-connected inverter contains high-frequency signals. If these signals are directly transmitted to the power grid, they may affect the normal operation of loads connected to the grid. To filter out these high-frequency signals, a filter capacitor is typically connected to the inverter's output. However, due to the inverter's operating time, operating environment (such as temperature and humidity), and operating conditions, the capacitance of this filter capacitor may decrease or even fail, affecting the inverter's operational stability and leading to unpredictable consequences.

[0006] Currently, most failure detection schemes for grid-connected inverters detect filter capacitor failures by monitoring the current flowing through the filter capacitor. When the filter capacitor fails or its capacitance degrades, it exhibits a low-resistance state, increasing the current flowing through it. When the current flowing through the filter capacitor exceeds a set threshold, the connection between the filter capacitor and the grid-connected inverter is disconnected, thereby ensuring the stable operation of the grid-connected inverter.

[0007] In practical applications, when the power grid is struck by lightning, the lightning energy will be released through the filter capacitor and other devices. At this time, the current of the filter capacitor will suddenly increase. This does not affect the filter capacitor's ability to filter high-frequency signals, but the detection device will assume that the filter capacitor has failed.

[0008] In summary, there is an urgent need for a fault detection scheme for filter capacitors to accurately detect whether filter capacitors have failed, so that the voltage output by the grid-connected inverter can be safely output to the power grid. Summary of the Invention

[0009] This application provides a fault detection device, method, and grid-connected photovoltaic power generation system to improve the accuracy of filter capacitor failure detection and ensure the stable operation of the grid-connected photovoltaic power generation system.

[0010] In a first aspect, embodiments of this application provide a fault detection device, which may include: a temperature detection unit, a current detection unit, and a controller.

[0011] The temperature detection unit is coupled to multiple filter capacitors between the output terminal of the grid-connected inverter and the power grid to detect the temperature of the multiple filter capacitors and output the temperature to the controller. The current detection unit is coupled to multiple filter capacitors to detect the current of the multiple filter capacitors and output the current to the controller. The controller is coupled to the temperature detection unit and the current detection unit respectively, and is used to disconnect the connection between the output terminal of the grid-connected inverter and the multiple filter capacitors when the received temperature exceeds a first threshold and the received current exceeds a second threshold.

[0012] Using the above fault detection scheme, if multiple filter capacitors fail or their capacitance decreases, they will exhibit low resistance, leading to an increase in the current flowing through them and a rise in their temperature. This results in increased current and temperature readings from both the current and temperature detection units. To prevent short circuits between the two phase lines, the controller disconnects the grid-connected inverter output from the multiple filter capacitors, ensuring safe operation of the inverter. If the grid is struck by lightning, the lightning energy needs to be filtered out by the multiple filter capacitors, causing an increase in the current reading from the current detection unit. However, the release time of the lightning energy is very short, while the temperature rise of the multiple filter capacitors requires a corresponding amount of time. Therefore, before the temperature reading from the temperature detection unit reaches the first threshold, the lightning energy has already been released, and the current reading from the current detection unit has already dropped to a normal value. The controller then maintains the connection between the grid-connected inverter output and the multiple filter capacitors, improving the fault detection accuracy of the fault detection device.

[0013] Specifically, the multiple filter capacitors include a first filter capacitor, a second filter capacitor, and a third filter capacitor. The first output terminal of the grid-connected inverter is connected to the first filter capacitor and the first phase line of the grid to form a first grid connection point. The second output terminal of the grid-connected inverter is connected to the second filter capacitor and the second phase line of the grid to form a second grid connection point. The third output terminal of the grid-connected inverter is connected to the third filter capacitor and the third phase line of the grid to form a third grid connection point.

[0014] In the above case, the temperature detection unit includes: a first temperature sensor, a second temperature sensor, and a third temperature sensor.

[0015] The first temperature sensor has one end coupled to the first filter capacitor and the other end connected to the controller, and is used to detect the temperature of the first filter capacitor and output it to the controller; the second temperature sensor has one end coupled to the second filter capacitor and the other end connected to the controller, and is used to detect the temperature of the second filter capacitor and output it to the controller; the third temperature sensor has one end coupled to the third filter capacitor and the other end connected to the controller, and is used to detect the temperature of the third filter capacitor and output it to the controller.

[0016] Using the above-mentioned fault detection device, the temperature of all filter capacitors can be detected by a temperature detection unit.

[0017] In one possible design, the current detection unit includes: a first current sensor, a second current sensor, and a third current sensor.

[0018] The first current sensor has one end coupled to the first filter capacitor and the other end connected to the controller, and is used to detect the current of the first filter capacitor and output it to the controller; the second current sensor has one end coupled to the second filter capacitor and the other end connected to the controller, and is used to detect the current of the second filter capacitor and output it to the controller; the third current sensor has one end coupled to the third filter capacitor and the other end connected to the controller, and is used to detect the current of the third filter capacitor and output it to the controller.

[0019] Using the above-mentioned fault detection device, the current flowing through all the filter capacitors can be detected by the current detection unit.

[0020] In one possible design, the fault detection device also includes a voltage detection unit connected to the controller.

[0021] The voltage detection unit is coupled to multiple filter capacitors to detect the voltage of the multiple filter capacitors and outputs the detected voltage to the controller.

[0022] With the addition of a voltage detection unit, the controller can determine the connection time between the grid-connected inverter output and multiple filter capacitors in the following way: when the received temperature exceeds a first threshold, the received current exceeds a second threshold, and the received voltage is outside the preset threshold range, the connection between the grid-connected inverter output and multiple filter capacitors is disconnected.

[0023] The aforementioned fault detection device, by employing a voltage detection unit to detect the filter capacitor when it fails, improves the accuracy of detecting filter capacitor failure, as the voltage across the filter capacitor changes when it fails.

[0024] In one possible design, the voltage detection unit includes: a first voltage sensor, a second voltage sensor, and a third voltage sensor.

[0025] The first voltage sensor has one end coupled to the first filter capacitor and the other end connected to the controller. It is used to detect the first voltage across the first filter capacitor and output the first voltage to the controller. The second voltage sensor has one end coupled to the second filter capacitor and the other end connected to the controller. It is used to detect the second voltage across the second filter capacitor and output the second voltage to the controller. The third voltage sensor has one end coupled to the third filter capacitor and the other end connected to the controller. It is used to detect the third voltage across the third filter capacitor and output the third voltage to the controller.

[0026] In one possible implementation, the protection detection device may further include a disconnection unit connected to a controller. This disconnection unit is connected between the grid-connected inverter output and multiple filter capacitors, and is used to disconnect or close under the control of the controller.

[0027] Specifically, depending on the connection method of the multiple filter capacitors, the disconnection unit can have the following two possible implementation methods:

[0028] Segmentation unit implementation method 1:

[0029] The first filter capacitor, the second filter capacitor, and the third filter capacitor are connected in a star configuration. The disconnection unit includes a first switch, a second switch, and a third switch.

[0030] Specifically, the first switch is connected between the first filter capacitor and the first output terminal to connect the first filter capacitor to the first output terminal; the second switch is connected between the second filter capacitor and the second output terminal to connect the second filter capacitor to the second output terminal; and the third switch is connected between the third filter capacitor and the third output terminal to connect the third filter capacitor to the third output terminal.

[0031] Method 2 for implementing segmentation units:

[0032] The first, second, and third filter capacitors are connected in a delta configuration, and the disconnection unit includes a fourth and a fifth switch.

[0033] The fourth switch is connected between the first filter capacitor and the first output terminal to connect the first filter capacitor to the first output terminal; the fifth switch is connected between the second filter capacitor and the second output terminal to connect the second filter capacitor to the second output terminal.

[0034] In one possible implementation, the controller is further configured to: detect the voltages of a first grid connection point, a second grid connection point, and a third grid connection point when it is determined that the received temperature exceeds a first threshold and the received current exceeds a second threshold; control a first switch to open when it is determined that the voltage of the first grid connection point is zero; control a second switch to open when it is determined that the voltage of the second grid connection point is zero; and control a third switch to open when it is determined that the voltage of the third grid connection point is zero.

[0035] By using the above-mentioned fault detection device, the first switch, the second switch, and the third switch can be turned off at zero voltage, thereby reducing the losses when the switches are disconnected.

[0036] Secondly, embodiments of this application provide a grid-connected photovoltaic power generation system, which includes: multiple photovoltaic modules, a grid-connected inverter, multiple filter capacitors, and the aforementioned fault detection device.

[0037] The system includes multiple photovoltaic modules connected to a grid-connected inverter to convert solar energy into direct current (DC) and output the DC to the inverter. The grid-connected inverter is connected to multiple filter capacitors and the power grid to convert the received DC into alternating current (AC) and output it to the power grid and the filter capacitors. The filter capacitors filter the received AC and output the filtered AC to the power grid. A fault detection device is coupled to the filter capacitors and connected to the grid-connected inverter and the power grid to detect whether the filter capacitors have failed. If a fault occurs, the device disconnects the filter capacitors from the power grid and the grid-connected inverter.

[0038] By using the above-mentioned grid-connected photovoltaic power generation system, the aforementioned fault detection device can accurately detect whether multiple filter capacitors have failed, ensuring that the electrical energy output by multiple photovoltaic modules can be accurately connected to the grid.

[0039] Thirdly, embodiments of this application provide a fault detection method, wherein the executing entity of the fault detection method may be the controller in the aforementioned fault detection device, and specifically includes the following steps:

[0040] The current and temperature of multiple filter capacitors between the output terminal of the grid-connected inverter and the grid are monitored; when the temperature of multiple filter capacitors exceeds a first threshold and the current of multiple filter capacitors exceeds a second threshold, the connection between multiple filter capacitors and the grid-connected inverter and the grid is disconnected.

[0041] Using the above method, the failure of multiple filter capacitors can be determined based on two factors: current and temperature. If the power grid is struck by lightning, the lightning energy needs to be filtered out by multiple filter capacitors, causing the current value detected by the current detection unit to rise. However, the release time of the lightning energy is very short, while the temperature of multiple filter capacitors needs a corresponding amount of time to rise. Therefore, before the temperature value detected by the temperature detection unit rises to the first threshold, the lightning energy has already been released, and the current value detected by the current detection unit has dropped to the normal value. The controller controls the disconnection unit to maintain the connection of the filter capacitors, thereby improving the fault detection accuracy of the fault detection device.

[0042] In one possible design, the method further includes: detecting the voltage of multiple filter capacitors; disconnecting the multiple filter capacitors from the grid-connected inverter and the grid when the temperature of the multiple filter capacitors exceeds a first threshold and the current of the multiple filter capacitors exceeds a second threshold, including: disconnecting the multiple filter capacitors from the grid-connected inverter and the grid when it is determined that the temperature of the multiple filter capacitors exceeds the first threshold, the current of the multiple filter capacitors exceeds the second threshold, and the voltage of the multiple filter capacitors is outside a preset threshold range.

[0043] Using the above method, since the failure of multiple filter capacitors will also cause changes in the voltage across multiple filter capacitors, the voltage across multiple filter capacitors will be detected and used as one of the conditions for determining whether the filter capacitors have failed.

[0044] In one possible implementation, the multiple filter capacitors include a first filter capacitor, a second filter capacitor, and a third filter capacitor. The first output terminal of the grid-connected inverter is connected to the first filter capacitor and the first phase line of the grid to form a first grid connection point. The second output terminal of the grid-connected inverter is connected to the second filter capacitor and the second phase line of the grid to form a second grid connection point. The third output terminal of the grid-connected inverter is connected to the third filter capacitor and the third phase line of the grid to form a third grid connection point.

[0045] When disconnecting multiple filter capacitors from the grid-connected inverter and the power grid, the voltages at the first, second, and third grid-connected points can be detected. When the voltage at the first grid-connected point is determined to be zero, the first filter capacitor is disconnected from the first phase line and the first output terminal. When the voltage at the second grid-connected point is determined to be zero, the second filter capacitor is disconnected from the second phase line and the second output terminal. When the voltage at the third grid-connected point is determined to be zero, the third filter capacitor is disconnected from the third phase line and the third output terminal. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of a photovoltaic power generation system provided in an embodiment of this application;

[0047] Figure 2A schematic diagram of a photovoltaic power generation system connected to the grid is provided as an embodiment of this application;

[0048] Figure 3 This is a schematic diagram of the connection of a filter capacitor provided in an embodiment of this application;

[0049] Figure 4 This is a schematic diagram of another filter capacitor connection provided in an embodiment of this application;

[0050] Figure 5 This is a schematic diagram of the structure of a fault detection device provided in an embodiment of this application;

[0051] Figure 6 This is a schematic diagram of another fault detection device provided in an embodiment of this application;

[0052] Figure 7 This is a schematic diagram of the structure of a temperature detection unit provided in an embodiment of this application;

[0053] Figure 8 This is a schematic diagram of the structure of a current detection unit provided in an embodiment of this application;

[0054] Figure 9 This is a schematic diagram of the structure of a voltage detection unit provided in an embodiment of this application;

[0055] Figure 10 This is a schematic diagram of the structure of a segmentation unit provided in an embodiment of this application;

[0056] Figure 11 This is a schematic diagram of another segmentation unit provided in an embodiment of this application;

[0057] Figure 12 This is a schematic diagram of the structure of a fault detection device provided in an embodiment of this application;

[0058] Figure 13 A flowchart illustrating a fault detection method provided in an embodiment of this application;

[0059] Figure 14 This is a schematic diagram of a grid-connected power generation system provided in an embodiment of this application. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this invention, "multiple" can also be understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order.

[0061] It should be noted that in the embodiments of this application, "connection" refers to electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components, such as the connection between A and B. Alternatively, it can be a direct connection between A and C, a direct connection between C and B, with A and B connected through C.

[0062] The fault detection device provided in this application embodiment can be applied to photovoltaic power generation systems. See [link to application details]. Figure 1 This is a schematic diagram of a photovoltaic power generation system applicable to an embodiment of this application. Figure 1 As shown, a photovoltaic power generation system mainly includes multiple photovoltaic modules and a grid-connected inverter.

[0063] Specifically, multiple photovoltaic (PV) modules are connected to a grid-connected inverter. Each PV module converts the received solar energy into direct current (DC) electrical energy and outputs this DC power to the grid-connected inverter. The grid-connected inverter then converts the received DC power into alternating current (AC) power and outputs it.

[0064] Specifically, in a photovoltaic power generation system, the output terminal of the grid-connected inverter is connected to the power grid to process the electrical energy generated by the photovoltaic power generation system for grid connection, thereby supplying power to loads connected to the grid. This power grid is a three-phase grid, and the connection point between the output terminal of the grid-connected inverter and the grid can be called the PCC or the grid connection point.

[0065] See Figure 2 The diagram shown is a grid connection schematic of a photovoltaic power generation system. Figure 2 As shown, the grid-connected inverter has three output ports, A, B and C, for outputting three-phase AC power.

[0066] Specifically, output port A is connected to phase A of the power grid to form the first grid connection point, output port B is connected to phase B of the power grid to form the second grid connection point, and output port C is connected to phase C of the power grid to form the third grid connection point. The aforementioned power grid is a three-phase power grid.

[0067] In practical applications, the AC output of a grid-connected inverter contains a large number of high-frequency signals. If these high-frequency signals are directly transmitted to the power grid, they will directly affect the power quality of the grid, and in severe cases, may even damage some precision loads connected to the grid. Therefore, multiple filter capacitors are usually installed at the grid connection point. These filter capacitors can filter out the high-frequency signals in the AC output of the grid-connected inverter, thereby ensuring the quality of the power output to the grid.

[0068] Specifically, filter capacitors are used to filter high-frequency signals in the AC output of grid-connected inverters. There are two main connection methods, which are explained below with reference to the accompanying drawings.

[0069] See Figure 3 The diagram shown illustrates one possible connection of a filter capacitor. Figure 3 As shown, a first filter capacitor C1 is connected between the output port A of the grid-connected inverter and the neutral wire (N); a second filter capacitor C2 is connected between the output port B of the grid-connected inverter and N; and a third filter capacitor C3 is connected between the output port C of the grid-connected inverter and N. It should be noted that N here can be N in a photovoltaic power generation system or N in the power grid; this application does not limit this.

[0070] It can be seen that the filter capacitors C1, C2 and C3 are connected in a star configuration.

[0071] See Figure 4 The diagram shown illustrates another possible connection for the filter capacitor. Figure 4 As shown, a filter capacitor C1 is connected between the output port A and the output port B of the grid-connected inverter, a filter capacitor C2 is connected between the output port B and the output port C of the grid-connected inverter, and a filter capacitor C3 is connected between the output port C and the output port A of the grid-connected inverter.

[0072] It can be seen that the filter capacitors C1, C2 and C3 are connected in a delta configuration.

[0073] It should be noted that, in the two connection methods of the filter capacitor mentioned above, the capacitance value of the filter capacitor can be set according to the output voltage of the grid-connected inverter and the application scenario of the photovoltaic power generation system. This application embodiment will not provide a detailed description of this.

[0074] In actual use, filter capacitors may fail after prolonged use or due to malfunction. There are two possible scenarios: first, the filter capacitor may be in an open-circuit state; second, the capacitance value of the filter capacitor may decrease or even drop to zero, resulting in a short circuit. When the filter capacitor fails and the second scenario occurs, it can lead to a short circuit at the grid connection point, that is, a short circuit between the two phase lines of the grid and the two output ports of the grid-connected inverter, directly affecting the safety of the photovoltaic power generation system and the loads connected to the grid.

[0075] Currently, filter capacitor failure detection mainly involves detecting the current flowing through the filter capacitor. The principle is that when a filter capacitor fails, causing its capacitance to decrease, the current flowing through it will increase. Therefore, if the current of any one of the three filter capacitors exceeds a set value, that filter capacitor is considered to have failed. However, in this field, there are various situations that can cause changes in the current flowing through the filter capacitor. For example, when a grid-connected inverter or the grid is struck by lightning, the lightning energy may be released through the filter capacitor connected to the grid connection point, causing a sudden increase in the current flowing through that filter capacitor exceeding the set value. In this case, the above-mentioned failure detection method would directly assume the filter capacitor has failed. However, after the filter capacitor releases the lightning energy and after the lightning energy dissipates, it can still perform its function of filtering high-frequency signals in the AC output of the grid-connected inverter. The filter capacitor has not been damaged or failed. Therefore, the accuracy of the above-mentioned filter capacitor failure detection method cannot be guaranteed.

[0076] In view of this, this application provides a fault detection device that can be applied to photovoltaic power generation systems. This device can not only meet the grid connection requirements of photovoltaic power generation systems, but also improve the accuracy of filter capacitor failure detection.

[0077] like Figure 5 As shown, the fault detection device 500 provided in this application embodiment mainly includes a temperature detection unit 501, a current detection unit 502, and a controller 503.

[0078] Among them, the temperature detection unit 501 is coupled to multiple filter capacitors between the output terminal of the grid-connected inverter and the power grid, the current detection unit 502 is coupled to multiple filter capacitors, and the controller 503 is connected to the temperature detection unit 501 and the current detection unit 502 respectively.

[0079] Specifically, the temperature detection unit 501 can be used to detect the temperature of multiple filter capacitors and output it to the controller 503; the current detection unit 502 can be used to detect the current of multiple filter capacitors and output it to the controller 503; the controller 503 can be used to disconnect the connection between the grid-connected inverter output terminal and multiple filter capacitors when the received temperature exceeds a first threshold and the received current exceeds a second threshold.

[0080] When using the fault detection device 500 provided in this application embodiment to detect whether multiple filter capacitors have failed, the failure of multiple filter capacitors can be accurately detected by two factors: temperature and current. For example, when a photovoltaic power generation system or power grid is struck by lightning and releases lightning energy through multiple filter capacitors, although the lightning energy will cause the current flowing through the multiple filter capacitors to suddenly increase beyond the second threshold, the temperature of the multiple filter capacitors needs time to accumulate. Before the temperature of the multiple filter capacitors rises to the first threshold, the lightning energy has already been released, causing the filter capacitors to be unable to simultaneously meet the set values ​​of both current and temperature parameters. Therefore, it can effectively avoid the situation of filter capacitor failure detection errors caused by lightning energy release and other reasons, improve the accuracy of filter capacitor failure detection, and thus ensure the normal grid connection of the photovoltaic power generation system.

[0081] As one possible implementation, the fault detection device 500 may also include a disconnection unit 504 connected to the controller 503. The disconnection unit 504 may be connected between the output of the grid-connected inverter and multiple filter capacitors, and may be disconnected or closed under the control of the controller 503.

[0082] Specifically, when the received temperature exceeds the first threshold and the received current exceeds the second threshold, the controller 503 can send a control signal to the disconnection unit 504. After receiving the control signal, the disconnection unit 504 disconnects the connection between the grid-connected inverter output terminal and multiple filter capacitors.

[0083] As another possible implementation, the photovoltaic power generation system also includes a disconnection device connected between the output of the grid-connected inverter and multiple filter capacitors, and the controller 503 can be connected to the disconnection device.

[0084] Specifically, when the received temperature exceeds the first threshold and the received current exceeds the second threshold, the controller 503 sends a control signal to the disconnection device. After receiving the control signal, the disconnection device disconnects the connection between the grid-connected inverter output terminal and multiple filter capacitors.

[0085] In practical applications, the fault detection device 500 can be fixed to the photovoltaic power generation system. Alternatively, the fault detection device 500 can be designed to be flexible and detachable, meaning the photovoltaic power generation system has a fixed interface through which the fault detection device 500 can connect. In this case, the fault detection device 500 can be considered a device independent of the photovoltaic power generation system.

[0086] During the grid connection process of a photovoltaic power generation system, if the filter capacitor fails, it will cause changes in several other parameters, such as the voltage across the multiple filter capacitors. To further improve the accuracy of filter capacitor failure detection, the fault detection device 500 provided in this application embodiment may further include a voltage detection unit 505 connected to the controller 503.

[0087] Specifically, the voltage detection unit 505 is coupled to multiple filter capacitors and can be used to detect the voltage of the multiple filter capacitors and output the detected voltage to the controller 503.

[0088] In Adoption Figure 6 When the fault detection device 500 detects whether the filter capacitor has failed, the controller 503 can be used to: control the disconnection unit 504 to disconnect when the received temperature exceeds the first threshold, the received current exceeds the second threshold, and the received voltage is outside the preset threshold range.

[0089] The specific structures of the temperature detection unit 501, current detection unit 502, voltage detection unit 505, disconnection unit 504, and controller 503 in the fault detection device 500 will be described below.

[0090] I. Temperature Detection Unit 501

[0091] The temperature detection unit 501 is coupled to multiple filter capacitors used to filter high-frequency signals and connected to the controller 503. It can be used to detect the temperature of the coupled multiple filter capacitors and output the detected temperature to the controller 503.

[0092] Specifically, the temperature detection unit 501 may include a first temperature sensor, a second temperature sensor, and a third temperature sensor.

[0093] The first temperature sensor has one end coupled to the first filter capacitor and the other end connected to the controller 503, and is used to detect the temperature of the first filter capacitor and output it to the controller 503; the second temperature sensor has one end coupled to the second filter capacitor and the other end connected to the controller 503, and is used to detect the temperature of the second filter capacitor and output it to the controller 503; the third temperature sensor has one end coupled to the third filter capacitor and the other end connected to the controller 503, and is used to detect the temperature of the third filter capacitor and output it to the controller 503.

[0094] It should be noted that the temperature sensor provided in this application embodiment can be a non-contact temperature sensor or a contact temperature sensor, and this application embodiment does not make a specific limitation.

[0095] The following is combined with Figure 3The following explanation will be based on the example of a patch-type temperature sensor in the temperature detection unit 501.

[0096] For ease of understanding, a specific example of the structure of the temperature detection unit 501 is given below.

[0097] See Figure 7 This is a schematic diagram of the structure of a temperature detection unit provided in an embodiment of this application. Figure 7 In this configuration, RT1 constitutes the first temperature sensor, RT2 constitutes the second temperature sensor, and RT3 constitutes the third temperature sensor. The temperature output terminals of RT1, RT2, and RT3 are connected to the controller 503.

[0098] Figure 7 The connection relationship of each device in the temperature detection unit shown can be as follows: RT1 is in contact with the first filter capacitor C1, RT2 is in contact with the second filter capacitor C2, RT3 is in contact with the third filter capacitor C3, and the temperature output ports of RT1, RT2 and RT3 are all connected to the controller 503.

[0099] In actual use, since RT1 is a surface-mount temperature sensor, RT1 can be attached to C1 to make contact between RT1 and the filter capacitor C1. Similarly, all temperature sensors can make contact with the filter capacitor.

[0100] use Figure 7 When the temperature detection unit shown detects the temperature of multiple filter capacitors, RT1 detects the temperature of filter capacitor C1 and outputs the detected temperature to controller 503 through the temperature output port of RT1. RT2 detects the temperature of filter capacitor C2 and outputs the detected temperature to controller 503 through the temperature output port of RT2. RT3 detects the temperature of filter capacitor C3 and outputs the detected temperature to controller 503 through the temperature output port of RT3.

[0101] Of course, the above description of the temperature detection unit structure is only an example. In practical applications, the temperature detection unit can also adopt other structures depending on the type of temperature sensor in the temperature detection unit. For example, the temperature detection unit can be a thermistor to detect the temperature of the filter capacitor.

[0102] II. Current Detection Unit 502

[0103] The current detection unit 502 is coupled to multiple filter capacitors used to filter high-frequency signals and connected to the controller 503. It can be used to detect the current flowing through the multiple filter capacitors and output the detected current to the controller 503.

[0104] The current detection unit 502 may include a first current sensor, a second current sensor, and a third current sensor.

[0105] Specifically, one end of the first current sensor is coupled to the first filter capacitor, and the other end is connected to the controller 503, for detecting the current of the first filter capacitor and outputting it to the controller 503; one end of the second current sensor is coupled to the second filter capacitor, and the other end is connected to the controller 503, for detecting the current of the second filter capacitor and outputting it to the controller 503; one end of the third current sensor is coupled to the third filter capacitor, and the other end is connected to the controller 503, for detecting the current of the third filter capacitor and outputting it to the controller 503.

[0106] It should be noted that the current sensor provided in this application embodiment can be a non-contact current sensor or a contact current sensor, and this application embodiment does not make a specific limitation.

[0107] The following is combined Figure 3 The following explanation will be based on the example of a current transformer in a non-contact temperature sensor, specifically the temperature sensor in the current detection unit 502.

[0108] For ease of understanding, a specific example of the structure of the current detection unit 502 is given below.

[0109] See Figure 8 This is a schematic diagram of the structure of a current detection unit provided in an embodiment of this application. Figure 8 In this configuration, A1 constitutes the first current sensor, A2 constitutes the second current sensor, and A3 constitutes the third current sensor. The current output ports of A1, A2, and A3 are connected to the controller 503.

[0110] Figure 8 The connection relationship of each device in the current detection unit shown can be as follows: the detection winding of A1 is wound on the branch where the filter capacitor C1 is located, and the current output port of A1 is connected to the controller 503; the detection winding of A2 is wound on the branch where the filter capacitor C2 is located, and the current output port of A2 is connected to the controller 503; the detection winding of A3 is wound on the branch where the filter capacitor C3 is located, and the current output port of A3 is connected to the controller 503.

[0111] use Figure 8 When the current detection unit shown detects the current flowing through multiple filter capacitors, A1 detects the current flowing through filter capacitor C1 and outputs the detected current to controller 503, A2 detects the current flowing through filter capacitor C2 and outputs the detected current to controller 503, and A3 detects the current flowing through filter capacitor C3 and outputs the detected current to controller 503.

[0112] Of course, the above description of the current detection unit structure is only an example. In practical applications, depending on the type of current sensor, the current detection unit can also use other structures to detect the current of the current filter capacitor. For example, the current sensor can be, but is not limited to, a shunt or a Hall sensor.

[0113] III. Voltage Detection Unit 505

[0114] The voltage detection unit 505 is coupled to multiple filter capacitors used to filter high-frequency signals and connected to the controller 503. It can be used to detect the voltage across the multiple coupled filter capacitors and output the detected voltage to the controller 503.

[0115] Specifically, the voltage detection unit 505 may include a first voltage sensor, a second voltage sensor, and a third voltage sensor.

[0116] The first voltage sensor has one end coupled to the first filter capacitor and the other end connected to the controller 503. It is used to detect the first voltage across the first filter capacitor and output the first voltage to the controller 503. The second voltage sensor has one end coupled to the second filter capacitor and the other end connected to the controller 503. It is used to detect the second voltage across the second filter capacitor and output the second voltage to the controller 503. The third voltage sensor has one end coupled to the third filter capacitor and the other end connected to the controller. It is used to detect the third voltage across the third filter capacitor and output the third voltage to the controller 503.

[0117] It should be noted that the voltage sensor provided in this application embodiment can be a non-contact voltage sensor or a contact voltage sensor, and this application embodiment does not make a specific limitation.

[0118] The following is combined Figure 3 The following explanation will be based on the example of a voltage transformer in a non-contact voltage sensor, specifically the voltage sensor in the voltage detection unit 505.

[0119] For ease of understanding, a specific example of the structure of the voltage detection unit 505 is given below.

[0120] See Figure 9 This is a schematic diagram of the structure of a voltage detection unit provided in an embodiment of this application. Figure 9 In this configuration, U1 constitutes the first voltage sensor, U2 constitutes the second voltage sensor, and U3 constitutes the third voltage sensor. The voltage output ports of U1, U2, and U3 are connected to the controller 503.

[0121] Figure 9The connection relationship of each device in the voltage detection unit shown can be as follows: the detection winding of U1 is connected in parallel across the first filter capacitor C1, and the voltage output port of U1 is connected to the controller 503; the detection winding of U2 is connected in parallel across the second filter capacitor C2, and the voltage output port of U2 is connected to the controller 503; the detection winding of U3 is connected in parallel across the third filter capacitor C3, and the voltage output port of U3 is connected to the controller 503.

[0122] use Figure 9 When the voltage detection unit shown detects the voltage across multiple filter capacitors, U1 detects the voltage across filter capacitor C1 and outputs the detected voltage to controller 503, U2 detects the voltage across filter capacitor C2 and outputs the detected voltage to controller 503, and U3 detects the voltage across filter capacitor C3 and outputs the detected voltage to controller 503.

[0123] Of course, the above description of the voltage detection unit structure is only an example. In practical applications, depending on the type of voltage sensor, the voltage detection unit can also use other structures to detect the voltage across the filter capacitor, such as a Hall sensor.

[0124] IV. Segmentation Unit 504

[0125] The disconnection unit 504 is connected between the output terminal of the grid-connected inverter and multiple filter capacitors, and is used to disconnect or close under the control of the controller 503.

[0126] Specifically, the disconnection unit 504 is connected between the grid connection point and the filter capacitor.

[0127] It should be understood that when the disconnection unit 504 is in the closed state, the output terminal of the grid-connected inverter is connected to multiple filter capacitors, and when the disconnection unit 504 is in the open state, the output terminal of the grid-connected inverter is disconnected from multiple filter capacitors.

[0128] In actual use, according to the above Figure 3 and Figure 4 The two connection methods for the filter capacitor in this application embodiment have two circuit structures for the disconnecting unit 504, as detailed below:

[0129] Structure 1:

[0130] If multiple filter capacitors are connected in a star configuration, the disconnection unit 504 may include a first switch, a second switch, and a third switch.

[0131] Specifically, the first switch is connected between the first filter capacitor and the first output terminal to connect the first filter capacitor to the first output terminal; the second switch is connected between the second filter capacitor and the second output terminal to connect the second filter capacitor to the second output terminal; and the third switch is connected between the third filter capacitor and the third output terminal to connect the third filter capacitor to the third output terminal.

[0132] The function of the first switch is to control the connection between the first filter capacitor and the first grid connection point; the function of the second switch is to control the connection between the second filter capacitor and the second grid connection point; and the function of the third switch is to control the connection between the third filter capacitor and the third grid connection point.

[0133] It should be noted that the switch in the embodiments of this application can be one or more of various types of switching transistors, such as relays, metal oxide semiconductor field effect transistors (MOSFETs), bipolar junction transistors (BJTs), and insulated gate bipolar transistors (IGBTs). These will not be listed individually in the embodiments of this application. Each switch can include a first electrode, a second electrode, and a control electrode, wherein the control electrode is used to control the switching on or off. When the switch is on, current can be transmitted between the first and second electrodes; when the switch is off, no current can be transmitted between the first and second electrodes. Taking a MOSFET as an example, the control electrode of the switch is the gate, the first electrode of the switch can be the source of the switch, and the second electrode can be the drain of the switch; alternatively, the first electrode can be the drain of the switch, and the second electrode can be the source of the switch.

[0134] The following is combined with Figure 3 The structure of the segmentation unit 504 in the embodiments of this application will be described.

[0135] See Figure 10 This is a schematic diagram of the structure of a segmentation unit provided in an embodiment of this application. Figure 10 In this circuit, K1 constitutes the first switch, K2 constitutes the second switch, and K3 constitutes the third switch.

[0136] Figure 10The connection relationship of each device in the shown disconnection unit can be as follows: the first electrode of K1 is connected to the first grid connection point, the second electrode of K2 is connected to one end of the filter capacitor C1, the first electrode of K2 is connected to the second grid connection point, the second electrode of K2 is connected to one end of the filter capacitor C2, the first electrode of K3 is connected to the third grid connection point, the second electrode of K3 is connected to one end of the filter capacitor, and the control electrodes of K1, K2 and K3 are all connected to the controller 503.

[0137] use Figure 10 When the disconnection unit controls the connection of the filter capacitor to the output terminal of the grid-connected inverter and the power grid, K1 is connected between the first grid connection point and the filter capacitor C1, K2 is connected between the second grid connection point and the filter capacitor C2, and K3 is connected between the third grid connection point and the filter capacitor C3. The control electrodes of K1, K2 and K3 respectively receive the control signals sent by the controller 503, and control the connection between the first grid connection point and the filter capacitor C1, the second grid connection point and the filter capacitor C2 and the third grid connection point and the filter capacitor C3 according to the control signals.

[0138] Structure 2:

[0139] If multiple filter capacitors are connected in a star-delta configuration, the disconnection unit 504 may include a fourth switch and a fifth switch.

[0140] Specifically, the fourth switch is connected between the first filter capacitor and the first output terminal to realize the connection between the first filter capacitor and the first output terminal;

[0141] The fifth switch is connected between the second filter capacitor and the second output terminal to connect the second filter capacitor and the second output terminal.

[0142] The fourth switch controls the connection between the filter capacitor and the first grid connection point; the fifth switch controls the connection between the second filter capacitor and the second grid connection point.

[0143] It should be noted that the connection positions of the aforementioned fourth and fifth switches are for illustrative purposes only. In actual use, the fourth and fifth switches can be connected between any two grid connection points and the filter capacitor.

[0144] The following is combined with Figure 3 The second structure of the segmentation unit 504 in the embodiments of this application will be described.

[0145] See Figure 11 This is a schematic diagram of the structure of a segmentation unit provided in an embodiment of this application. Figure 11 In the middle, K4 constitutes the fourth switch, and K5 constitutes the fifth switch.

[0146] Figure 11The connection relationship of each device in the shown disconnection unit can be as follows: the first electrode of K4 is connected to the first grid connection point, the second electrode of K4 is connected to one end of the filter capacitor C1, the first electrode of K5 is connected to the second grid connection point, the second electrode of K5 is connected to one end of the filter capacitor C2, and the control electrodes of K4 and K5 are both connected to the controller 503.

[0147] V. Controller 503

[0148] The controller 503 is connected to the temperature detection unit 501, the current detection unit 502, the voltage detection unit 505 and the disconnection unit 504 respectively. The controller 503 can receive the temperature detected by the temperature detection unit 501, the current detected by the current detection unit 502 and the voltage detected by the voltage detection unit 505, and control the disconnection unit 504 to disconnect when the received temperature exceeds the first threshold, the received current exceeds the second threshold and the received voltage is outside the preset threshold range.

[0149] In practical applications, since the disconnection unit consists of switches, the controller 503 can adjust the operating state of the disconnection unit 504 by adjusting the on / off state of the switches. That is, the controller 503 can be used to connect the grid-connected inverter to multiple filter capacitors by controlling the on / off state of the disconnection unit 504, and to control the disconnection unit to close, thereby connecting the grid-connected inverter to multiple filter capacitors.

[0150] Specifically, if the switches in each circuit of the disconnection unit 504 are MOSFETs, the controller 503 can be connected to the gate of the MOSFET, thereby controlling the connection of multiple filter capacitors to the output terminal of the grid-connected inverter by controlling the on and off state of the MOSFET; if the switches in each circuit of the disconnection unit 504 are BJTs, the controller 503 can be connected to the base of the BJT, thereby controlling the connection of multiple filter capacitors to the output terminal of the grid-connected inverter by controlling the on and off state of the BJT.

[0151] In a specific implementation, the controller 503 can be any of a microcontroller unit (MCU), a central processing unit (CPU), or a digital signal processor (DSP). Of course, the specific form of the controller 503 is not limited to the examples mentioned above.

[0152] In actual use, since the output of the grid-connected inverter connected to the disconnection unit is a three-phase AC power whose phase and amplitude are constantly changing, in order to further reduce the losses of the switching on and off in the connected disconnection unit 504, the controller 503 can detect the voltage of the first grid connection point, the second grid connection point and the third grid connection point when it determines that the received temperature exceeds the first threshold and the received current exceeds the second threshold. When it determines that the voltage value of the first grid connection point is zero, it controls the first switch to open; when it determines that the voltage value of the second grid connection point is zero, it controls the second switch to open; and when it determines that the voltage value of the third grid connection point is zero, it controls the third switch to open.

[0153] It should be understood that by controlling the disconnection time of the switch in the disconnection unit 504 in the above manner, the switch in the disconnection unit 504 can be disconnected with zero voltage, thereby reducing the switching losses of the disconnection unit 504.

[0154] Based on the above description, for example, the fault detection device provided in the embodiments of this application can, as follows: Figure 12 As shown.

[0155] The temperature detection unit includes temperature sensors RT1, RT2, and RT3. RT1 is in contact with filter capacitor C1, RT2 is in contact with filter capacitor C2, and RT3 is in contact with filter capacitor C3. The temperature output ports of RT1, RT2, and RT3 are connected to the controller 503.

[0156] The current detection unit includes current sensors A1, A2, and A3. The detection winding of A1 is wound on the branch containing the filter capacitor C1, the detection winding of A2 is wound on the branch containing the filter capacitor C2, and the detection winding of A3 is wound on the branch containing the filter capacitor C3. The current output ports of A1, A2, and A3 are all connected to the controller.

[0157] The voltage detection unit includes voltage sensors U1, U2, and U3. The detection winding of U1 is connected in parallel across the filter capacitor C1, the detection winding of U2 is connected in parallel across the filter capacitor C2, and the detection winding of U3 is connected in parallel across the filter capacitor C3. The voltage output ports of U1, U2, and U3 are all connected to the controller.

[0158] The disconnection unit includes switches K1, K2, and K3. K1 is connected between the first grid connection point and the filter capacitor C1, K2 is connected between the second grid connection point and the filter capacitor C2, and K3 is connected between the third grid connection point and the filter capacitor C3. The control electrodes of K1, K2, and K3 are all connected to the controller.

[0159] use Figure 12When the fault detection device shown detects whether filter capacitors C1, C2, and C3 are faulty, RT1, RT2, and RT3 detect the temperature of the three filter capacitors and output the detected temperature to the controller. A1, A2, and A3 detect the current flowing through the three filter capacitors and output the detected current to the controller. U1, U2, and U3 detect the voltage across the three filter capacitors and output the detected voltage to the controller. When any of the three received temperatures exceeds the first threshold, any of the three received currents exceeds the second threshold, and any of the three received voltages is outside the set threshold range, the controller controls K1, K2, and K3 to disconnect. At this time, the filter capacitors are disconnected from the grid-connected inverter, thereby ensuring that the AC power output by the grid-connected inverter is normally connected to the grid.

[0160] Optionally, after the controller disconnects K1, K2 and K3, an alarm signal is sent to alert the user that the filter capacitor has failed.

[0161] Of course, the above description of the fault detection unit structure is only an example. In actual applications, the fault detection unit may also adopt other structures depending on the different components in the temperature detection unit, voltage detection unit, and current detection unit, as well as the different connection methods of the filter capacitor. These will not be described in detail here.

[0162] Specifically, for the aforementioned fault detection device, the controller can perform the following actions: Figure 13 The fault detection method shown accurately detects whether the filter capacitor has failed, ensuring that the AC output of the grid-connected inverter is normally connected to the grid. It mainly includes the following steps:

[0163] S1301: Detects the current and temperature of multiple filter capacitors between the output of the grid-connected inverter and the power grid.

[0164] S1302: When the temperature of multiple filter capacitors exceeds the first threshold and the current of multiple filter capacitors exceeds the second threshold, disconnect the multiple filter capacitors from the grid-connected inverter and the power grid.

[0165] It should be understood that since the output of the grid-connected inverter is a three-phase AC power whose amplitude and phase are constantly changing, when disconnecting multiple filter capacitors from the grid-connected inverter and the power grid, the connection of the filter capacitor can be disconnected when the voltage of the AC power of the phase connected to the filter capacitor is zero.

[0166] Specifically, before disconnecting multiple filter capacitors from the grid-connected inverter and the grid, the voltages at the first, second, and third grid-connected points are detected. When the voltage at the first grid-connected point is determined to be zero, the first filter capacitor is disconnected from the first phase line and the first output terminal. When the voltage at the second grid-connected point is determined to be zero, the second filter capacitor is disconnected from the second phase line and the second output terminal. When the voltage at the third grid-connected point is determined to be zero, the third filter capacitor is disconnected from the third phase line and the third output terminal.

[0167] It should be understood that since the failure of the filter capacitor will also cause a change in the voltage across the filter capacitor, in order to accurately detect whether the filter capacitor has failed, the aforementioned fault detection method can also detect the voltage of multiple filter capacitors. When the temperature of multiple filter capacitors exceeds the first threshold, the current of multiple filter capacitors exceeds the second threshold, and the voltage of multiple filter capacitors is outside the preset threshold range, the connection between multiple filter capacitors and the grid-connected inverter and the grid is disconnected.

[0168] As can be seen from the above embodiments, based on the fault detection device 500 provided in this application embodiment, since the failure of the filter capacitor will cause changes in multiple parameters, the controller 503 can accurately detect the failure of the filter capacitor based on the current flowing through the filter capacitor, the voltage across the filter capacitor, and the temperature of the filter capacitor. Therefore, using the embodiments of this application... Figure 13 The fault detection method shown is helpful to further improve the accuracy of filter capacitor failure detection.

[0169] It should be understood that the above-mentioned fault detection device and fault detection method can also be used in other fields, such as wind power generation, hydropower generation, thermal power generation and other fields where the generated electricity needs to be connected to the grid. The above-mentioned device and method can be used to accurately detect whether the filter capacitor used to filter high-frequency signals has failed.

[0170] Based on the above description, this application provides a grid-connected inverter, such as... Figure 14 As shown, the grid-connected inverter may include multiple photovoltaic modules 1401, a grid-connected inverter 1402, multiple filter capacitors 1403, and the aforementioned fault detection device 500.

[0171] Multiple photovoltaic modules 1401 are connected to a grid-connected inverter 1402 to convert solar energy into direct current (DC) and output the DC to the inverter 1402. The grid-connected inverter 1402 is connected to multiple filter capacitors 1403 and the power grid to convert the received DC into alternating current (AC) and output it to the power grid and the filter capacitors 1403. The filter capacitors 1403 filter the received AC and output the filtered AC to the power grid. A fault detection device 500 is coupled to the filter capacitors 1403 and connected to the grid-connected inverter 1402 and the power grid. It detects whether the filter capacitors 1403 have failed and disconnects them from the power grid and the inverter 1402 when they fail.

[0172] Optionally, the grid-connected photovoltaic power generation system 1400 may also include an energy storage battery 1404. The energy storage battery 1404 can store the excess electrical energy generated by the multiple photovoltaic modules 1401 when the electrical energy generated by the multiple photovoltaic modules 1401 is greater than the electrical energy demanded by the grid, and output the stored electrical energy to the grid through the grid-connected inverter 1402 when the electrical energy generated by the multiple photovoltaic modules 1401 is less than the electrical energy demanded by the grid.

[0173] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A grid-connected photovoltaic power generation system, characterized in that, It includes a grid-connected inverter, multiple filter capacitors, a disconnection unit, and a controller; among which, The grid-connected inverter is used to convert the direct current output by the photovoltaic module into alternating current and transmit the alternating current to the plurality of filter capacitors; The plurality of filter capacitors are used to filter the AC power and transmit the filtered AC power to the power grid; The disconnection unit is connected between the grid-connected inverter and the plurality of filter capacitors; The controller is configured to control the disconnection unit to disconnect when the temperature of the plurality of filter capacitors exceeds a first threshold and the current of the plurality of filter capacitors exceeds a second threshold.

2. The grid-connected photovoltaic power generation system according to claim 1, characterized in that, The controller is also used to control the disconnection unit to disconnect when the voltage of the plurality of filter capacitors is outside a preset threshold range.

3. The grid-connected photovoltaic power generation system according to claim 1 or 2, characterized in that, The grid-connected inverter includes a first output terminal, a second output terminal, and a third output terminal; the plurality of filter capacitors include a first filter capacitor, a second filter capacitor, and a third filter capacitor; and the disconnect switch includes a first switch, a second switch, and a third switch. The first filter capacitor, the second filter capacitor, and the third filter capacitor are connected in a star configuration. The first switch is connected between the first filter capacitor and the first output terminal; the second switch is connected between the second filter capacitor and the second output terminal; and the third switch is connected between the third filter capacitor and the third output terminal.

4. The grid-connected photovoltaic power generation system according to claim 1 or 2, characterized in that, The grid-connected inverter includes a first output terminal, a second output terminal, and a third output terminal; the plurality of filter capacitors include a first filter capacitor, a second filter capacitor, and a third filter capacitor; and the disconnect switch includes a fourth switch and a fifth switch. The first filter capacitor, the second filter capacitor, and the third filter capacitor are connected in a triangle. The fourth switch is connected between the first filter capacitor and the first output terminal, and the fifth switch is connected between the second filter capacitor and the second output terminal.

5. The grid-connected photovoltaic power generation system according to claim 3 or 4, characterized in that, The first output terminal, the second output terminal, and the third output terminal are respectively connected to the three phase lines of the power grid.

6. The grid-connected photovoltaic power generation system according to any one of claims 1-5, characterized in that, The grid-connected photovoltaic power generation system also includes a current detection unit, which is used to detect the current flowing through the plurality of filter capacitors.

7. The grid-connected photovoltaic power generation system according to any one of claims 1-5, characterized in that, The grid-connected photovoltaic power generation system also includes a temperature detection unit, which is used to detect the temperature of the plurality of filter capacitors.

8. The grid-connected photovoltaic power generation system according to claim 6 or 7, characterized in that, When the grid-connected photovoltaic power generation system includes a current detection unit, the controller is used to receive information collected by the current detection unit; when the grid-connected photovoltaic power generation system includes a temperature detection unit, the controller is used to receive information collected by the temperature detection unit.

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