Relay fault detection circuit of grid-connected inverter, detection method and grid-connected system

Abstract

The invention discloses a relay fault detection circuit of a grid-connected inverter, a detection method and a grid-connected system, when fault detection needs to be carried out on relays, a first controller and a second controller communicate with each other to cooperate to sequentially execute each fault detection process, and simultaneous adhesion fault detection is carried out on main and auxiliary relays on each phase line; the method comprises the following steps of: detecting the adhesion fault of an auxiliary relay on each phase line, detecting the adhesion fault of each relay on a neutral line and detecting the adhesion fault of a main relay on each phase line, and finally detecting the closing fault of each relay. According to the fault detection method, the control actions of the first controller and the second controller in the fault detection process are reasonably distributed through the fault detection process, and compared with the prior art, the detection time can be shortened, and the reliability of the detection process is also ensured.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and particularly to a relay fault detection circuit, a detection method and a grid-connected system for a grid-connected inverter. Background Art

[0002] Grid-connected inverters are commonly seen in household grid-connected systems. The energy storage unit of a household grid-connected system can output electric energy to the power grid or draw power from the power grid for use in the system through the grid-connected inverter. During use, it is necessary to ensure reliable separation between the household grid-connected system and the power grid. Therefore, two-stage relays are usually connected to the cable between the inverter output and the power grid, and it is required that the system can detect the sticking faults and closing faults of all relays before operation.

[0003] A three-phase grid-connected inverter requires at least six relays. Before the system operates, the controller sends control commands to each relay to indicate the relay to open or close, and it is necessary to obtain the electrical signals measured during the detection process. The whole process is relatively complex, the logic control task is large, which increases the detection time and reduces the reliability of the detection process. Summary of the Invention

[0004] The present embodiment provides a relay fault detection circuit, a detection method and a grid-connected system for a grid-connected inverter, which can shorten the detection duration and ensure the reliability of the detection process.

[0005] In a first aspect, an embodiment of the present application provides a relay fault detection circuit for a grid-connected inverter. There are L1 phase line, L2 phase line, L3 phase line and neutral line connected between the grid-connected inverter and the power grid. The fault detection circuit includes: A relay group, including a first main relay and a first auxiliary relay connected in sequence on the L1 phase line, a second main relay and a second auxiliary relay connected in sequence on the L2 phase line, a third main relay and a third auxiliary relay connected in sequence on the L3 phase line, and a fourth relay, a fifth relay and a sixth relay connected in sequence on the neutral line; An inverter-side voltage detection module for collecting the inverter-side voltage; A grid-side voltage detection module for collecting the grid-side voltage; A first controller for controlling the opening and closing of each main relay, the fourth relay and the fifth relay, and also for obtaining the inverter-side voltage through the inverter-side voltage detection module and obtaining the grid-side voltage through the grid-side voltage detection module; A second controller, communicatively connected to the first controller, for controlling the opening and closing of each auxiliary relay and the sixth relay.

[0006] Second aspect, embodiments of the present application provide a relay fault detection method for a grid-connected inverter, which is applied to the relay fault detection circuit as described in the first aspect. The fault detection method includes: Before the grid-connected inverter starts, the first controller and the second controller cooperate to perform fault detection in the following stages in sequence: Disconnect all relays to detect whether the main relays and auxiliary relays on each phase line are simultaneously stuck; Disconnect the auxiliary relays to detect whether the auxiliary relays on each phase line are stuck; Disconnect the relay on the neutral line to detect whether the relay on the neutral line is stuck; Disconnect the main relays to detect whether the main relays on each phase line are stuck; Disconnect the fourth relay to detect whether each relay in the relay group is closed; When all the fault detection stages are passed, it is determined that there are no stuck and closed faults in the relays in the relay group.

[0007] In some embodiments, the step of disconnecting all relays to detect whether the main relays and auxiliary relays on each phase line are simultaneously stuck includes: Disconnect the main relays, the fourth relay, and the fifth relay on each phase line, and instruct the second controller to disconnect the auxiliary relays and the sixth relay on each phase line; Obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than the first threshold, it is determined that the main relay and the auxiliary relay on the corresponding phase line are simultaneously stuck.

[0008] In some embodiments, the step of disconnecting the auxiliary relays to detect whether the auxiliary relays on each phase line are stuck includes: Close the main relays, the fourth relay, and the fifth relay, and instruct the second controller to close the sixth relay, and disconnect the first auxiliary relay, the second auxiliary relay, and the third auxiliary relay; Obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than the first threshold, it is determined that the auxiliary relay on the corresponding phase line is stuck.

[0009] In some embodiments, the step of disconnecting the relay on the neutral line to detect whether the relay on the neutral line is stuck includes: Close the first main relay, the fourth relay, and the fifth relay, open the second main relay and the third main relay, and instruct the second controller to close each auxiliary relay and open the sixth relay; Obtain the inverter-side voltage and the grid-side voltage of the L1 phase line; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is less than the first threshold, determine that the sixth relay has a sticking fault; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is greater than the first threshold, open the fifth relay and instruct the second controller to close the sixth relay; Obtain the inverter-side voltage and the grid-side voltage of the L1 phase line; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is less than the first threshold, determine that the fifth relay has a sticking fault; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is greater than the first threshold, open the fourth relay and close the fifth relay; Obtain the inverter-side voltage and the grid-side voltage of the L1 phase line; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is less than the first threshold, determine that the fourth relay has a sticking fault.

[0010] In some embodiments, the opening of the main relay to detect whether there is a sticking fault in the main relays on each phase line includes: Close the fourth relay and the fifth relay, open each main relay, and instruct the second controller to close each auxiliary relay and the sixth relay; Obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than the first threshold, determine that there is a sticking fault in the main relay on the corresponding phase line.

[0011] In some embodiments, the opening of the fourth relay to detect whether there is a closing fault in each relay of the relay group includes: Close each main relay and the fifth relay, open the fourth relay, and instruct the second controller to close each auxiliary relay and the sixth relay; Obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; When the difference between the voltage on the inverter side and the voltage on the grid side of any phase line is greater than a second threshold value, it is determined that the main relay on the corresponding phase line has an adhesion fault.

[0012] In some embodiments, the fault detection method further includes: When a fault is detected in the fault detection process of any stage, exit the fault detection process and issue a fault prompt.

[0013] In a third aspect, an embodiment of the present application provides a controller, including at least one processor and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the fault detection method as described in the second aspect.

[0014] In a fourth aspect, an embodiment of the present application provides a grid-connected system, including the controller as described in the third aspect.

[0015] In a fifth aspect, an embodiment of the present application provides a computer-readable storage medium, which stores computer-executable instructions for causing a computer to execute the fault detection method as described in the second aspect.

[0016] The relay fault detection circuit, detection method and grid-connected system of the grid-connected inverter in this embodiment have at least the following beneficial effects: In the embodiment of the present application, the first controller controls the opening and closing of each main relay, fourth relay and fifth relay, and the second controller controls the opening and closing of each auxiliary relay and sixth relay. The first controller, as the main controller, communicates with the second controller and receives the inverter-side voltage measured by the inverter-side voltage detection module and the grid-side voltage measured by the grid-side voltage detection module. This can reduce the control complexity of the second controller and ensure the stable operation of the second controller as a standby controller; when it is necessary to perform fault detection on the relay, the first controller and the second controller communicate with each other to cooperate and sequentially execute each fault detection process. First, perform the simultaneous adhesion fault detection of the main and auxiliary relays on each phase line, then perform the adhesion fault detection of the auxiliary relays on each phase line, the adhesion fault detection of each relay on the neutral line and the adhesion fault detection of the main relays on each phase line, and finally perform the closing fault detection of each relay. When the first controller determines that all the above fault detection stages have passed, it is determined that all the relays in the relay group have no adhesion faults and closing faults, and the grid-connected inverter can start working normally. Through the above fault detection process, the control actions of the first controller and the second controller in the fault detection process are reasonably allocated, which can shorten the detection time compared with the prior art and ensure the reliability of the detection process. Description of the Drawings

[0017] Figure 1 is the circuit diagram of the relay fault detection circuit provided by the embodiments of the present application; Figure 2 is the overall flowchart of the relay fault detection method provided by the embodiments of the present application; Figure 3 is the flowchart of the first stage of the relay fault detection provided by the embodiments of the present application; Figure 4 is the flowchart of the second stage of the relay fault detection provided by the embodiments of the present application; Figure 5 is the flowchart of the third stage of the relay fault detection provided by the embodiments of the present application; Figure 6 is the flowchart of the fourth stage of the relay fault detection provided by the embodiments of the present application; Figure 7 is the flowchart of the fifth stage of the relay fault detection provided by the embodiments of the present application; Figure 8 is the schematic diagram of the connection structure of the controller provided by the embodiments of the present application. Detailed implementation manners

[0018] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Additionally, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. At the same time, the steps or actions in the method description can also be reordered or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0019] In the description of the present application, the meaning of several is one or more, the meaning of multiple is two or more, greater than, less than, exceeding, etc. are understood as not including the number itself, and above, below, within, etc. are understood as including the number. If it is described as first, second, etc., it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence of the indicated technical features.

[0020] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the described objects and do not have any sequential or technical meaning. And the "connection" and "coupling" mentioned in the present application, unless otherwise specified, both include direct and indirect connection (coupling).

[0021] The grid-connected inverter connects the low-voltage side system and the high-voltage side system. The low-voltage side system is usually a household energy storage system, including photovoltaic solar panels, lithium battery packs, etc. The high-voltage side system is usually the power grid. The low-voltage side system can transmit power to the power grid through the grid-connected inverter to reduce the power consumption burden of the power grid, or can draw power from the power grid through the grid-connected inverter to make up for the instability of the power supply on the low-voltage side system or solve the problem that the lithium battery pack has a low power level and cannot supply power. Therefore, the stable operation of the grid-connected inverter is crucial for the low-voltage side system and the high-voltage side system.

[0022] Currently, the connection between the grid-connected inverter and the grid side usually requires connecting three phase lines and a neutral line. Before the grid-connected inverter operates, it is necessary to ensure that the switches on the three phase lines and the neutral line can work properly, so that the grid-connected inverter can be connected to the grid and can be reliably separated from the grid. These switches usually use relays, and the switch control is achieved through the energization and de-energization of the relays. To further ensure reliable separation, two-stage relays are usually set, that is, two relays are set on each phase line. When one relay fails to disconnect, the other relay can be used to disconnect.

[0023] It can be seen from this that there are a large number of relays between the grid-connected inverter and the power grid, and these relays need to be fault-detected before the grid-connected inverter operates. Currently, the fault detection scheme is relatively complex, or it can only detect stuck faults and cannot detect closed faults, or some fault conditions cannot be detected.

[0024] For example, in the related art, a U-phase, a V-phase, a W-phase, and an N-phase are set between an inverter and a power grid. A first main relay and a second auxiliary relay are set in the U-phase, a second main relay and a second auxiliary relay are set in the V-phase, a third main relay and a third auxiliary relay are set in the W-phase. A differential sampling circuit is further set to perform voltage sampling on the midpoints of the first main relay and the second auxiliary relay, the midpoints of the second main relay and the second auxiliary relay, and the midpoints of the third main relay and the third auxiliary relay. The midpoint of the first main relay and the second auxiliary relay is connected to the N-phase through a resistor, the midpoint of the second main relay and the second auxiliary relay is connected to the N-phase through a resistor, and the midpoint of the third main relay and the third auxiliary relay is connected to the N-phase through a resistor. During the fault detection process, different relays are combined in switches and the inverter is controlled whether to output an open-loop voltage, and the difference between the voltage sampling value of the differential sampling circuit and the voltage value on the power grid side is judged, and then whether the relay on the corresponding phase line fails is judged. In this solution, it is necessary to consider that the voltage sampling point of the differential sampling circuit is located between the main and auxiliary relays, and a resistor needs to be connected to the N-line, and the circuit is relatively complex. In terms of the control method, since the main relay is between the inverter and the voltage sampling point of the differential sampling circuit, it is necessary to control whether the inverter outputs an open-loop voltage to cooperate with the judgment, and the control logic is complex. At the same time, when the final detection is completed, the three main relays are disconnected and the three auxiliary relays are closed. It is necessary to control the main relay and the auxiliary relay to close in sequence again to connect the inverter to the power grid, which increases the detection time.

[0025] Based on this, this embodiment provides a relay fault detection circuit, a detection method, and a grid-connected system for a grid-connected inverter. In terms of the circuit structure, main relays and auxiliary relays are set on the L1 phase line, the L2 phase line, and the L3 phase line, and three relays are also set on the neutral line. The first controller is responsible for controlling the main relay and the two relays on the neutral line, and the second controller is responsible for controlling the auxiliary relay and the remaining one relay on the neutral line. The first controller and the second controller communicate to cooperate in controlling the switch combination of the relays. During the detection process, first, it is detected whether the main and auxiliary relays on each phase line simultaneously have an adhesion fault. If not, it is judged whether the auxiliary relays on each phase line have an adhesion fault. If not, it is judged whether the three relays on the neutral line have an adhesion fault. If not, it is judged whether the main relays on each phase line have an adhesion fault. If not, finally, it is judged whether each relay in the relay group has a closing fault. After all the above fault tests pass, only closing the fourth relay can connect the grid-connected inverter to the power grid. The overall control logic is clear, which ensures the reliability of the detection process and shortens the detection time.

[0026] The relay fault detection circuit, the detection method, and the grid-connected system for the grid-connected inverter will be described in detail below with reference to the accompanying drawings: Refer to Figure 1 as shown,Figure 1 This is the circuit diagram of the relay fault detection circuit provided by the embodiments of the present application. For the relay fault detection circuit of the grid-connected inverter in the embodiments of the present application, an L1 phase line, an L2 phase line, an L3 phase line, and a neutral line are connected between the grid-connected inverter and the power grid. The fault detection circuit includes: A relay group, including a first main relay K11 and a first sub-relay K12 connected in sequence on the L1 phase line, a second main relay K21 and a second sub-relay K22 connected in sequence on the L2 phase line, a third main relay K31 and a third sub-relay K32 connected in sequence on the L3 phase line, and a fourth relay K4, a fifth relay K5, and a sixth relay K6 connected in sequence on the neutral line; An inverter-side voltage detection module for collecting the inverter-side voltage; A grid-side voltage detection module for collecting the grid-side voltage; A first controller for controlling the opening and closing of each main relay, the fourth relay K4, and the fifth relay K5, and also for obtaining the inverter-side voltage through the inverter-side voltage detection module and the grid-side voltage through the grid-side voltage detection module; A second controller communicatively connected to the first controller for controlling the opening and closing of each sub-relay and the sixth relay K6.

[0027] A relay group is arranged between the grid-connected inverter and the power grid. On the basis of arranging two-stage relays on the L1 phase line, the L2 phase line, and the L3 phase line, the relay group also arranges the fourth relay K4, the fifth relay K5, and the sixth relay K6 on the neutral line. That is to say, on the L1 phase line, in the direction from the grid-connected inverter to the power grid, the first main relay K11 and the first sub-relay K12 are arranged in sequence. On the L2 phase line, in the direction from the grid-connected inverter to the power grid, the second main relay K21 and the second sub-relay K22 are arranged in sequence. On the L3 phase line, in the direction from the grid-connected inverter to the power grid, the third main relay K31 and the third sub-relay K32 are arranged in sequence. On the neutral line, in the direction from the grid-connected inverter to the power grid, the fourth relay K4, the fifth relay K5, and the sixth relay K6 are arranged in sequence.

[0028] In order to reduce the operation burden of the controller and improve the ability of reliable separation between the grid-connected inverter and the power grid, a first controller and a second controller are set to control a part of the relays respectively. The first controller is the main controller, and the second controller is the auxiliary controller. The first controller is connected to the first main relay K11, the second main relay K21, the third main relay K31, the fourth relay K4, and the fifth relay K5 for controlling the closing and opening of these five relays. The second controller is connected to the first sub-relay K12, the second sub-relay K22, the third sub-relay K32, and the sixth relay K6 for controlling the closing and opening of these four relays.

[0029] An inverter-side grid detection module is also provided between the grid-connected inverter and the relay group, that is, voltage detection modules are respectively arranged on the L1 phase line, the L2 phase line and the L3 phase line. The whole of these voltage detection modules is the inverter-side grid detection module. For example, it includes a first voltage detection module, a second voltage detection module and a third voltage detection module. The first voltage detection module is arranged between the grid-connected inverter and the first main relay K11, the second voltage detection module is arranged between the grid-connected inverter and the second main relay K21, and the third voltage detection module is arranged between the grid-connected inverter and the third main relay K31; A grid-side voltage detection module is also provided between the relay group and the grid, that is, voltage detection modules are respectively arranged on the L1 phase line, the L2 phase line and the L3 phase line. The whole of these voltage detection modules is the grid-side detection module. For example, it includes a fourth voltage detection module, a fifth voltage detection module and a sixth voltage detection module. The fourth voltage detection module is arranged between the grid and the first auxiliary relay K12, the fifth voltage detection module is arranged between the grid and the second auxiliary relay K22, and the sixth voltage detection module is arranged between the grid and the third auxiliary relay K32.

[0030] The first controller is also connected to the inverter-side voltage detection module and the grid-side voltage detection module, receives the inverter-side voltage collected by the inverter-side voltage detection module and the grid-side voltage collected by the grid-side voltage detection module. The first controller judges the result of the fault detection process according to the inverter-side voltage and the grid-side voltage, combined with the opening and closing of each relay in the current relay group. It can be seen that the first controller, as the main controller in the fault detection process, is responsible for more relay opening and closing control and voltage signal operation, while the burden of the second controller is smaller. When the first controller fails and cannot control each main relay, the second controller, not affected by the failure of the first controller, can independently disconnect each auxiliary relay, thus ensuring the reliable separation of the grid-connected inverter and the grid. It can be understood that the first controller and the second controller are communicatively connected for information interaction. During the fault detection process, the first controller needs to coordinate with the second controller to control, so as to realize the opening and closing combination of different relays in the relay group.

[0031] Refer to Figure 2 As shown, the embodiment of the present application also provides a relay fault detection method for a grid-connected inverter, which is applied to the first controller in the above relay fault detection circuit. The fault detection method includes but is not limited to the following steps: Before the grid-connected inverter starts, cooperate with the second controller to perform fault detection in the following stages in sequence: Step S100, disconnect all relays to detect whether the main relays and auxiliary relays on each phase line are simultaneously stuck. Step S200, disconnect the auxiliary relay to detect whether there is an adhesion fault in the auxiliary relays on each phase line; Step S300, disconnect the relay on the neutral line to detect whether there is an adhesion fault in the relay on the neutral line; Step S400, disconnect the main relay to detect whether there is an adhesion fault in the main relays on each phase line; Step S500, disconnect the fourth relay K4 to detect whether there is a closing fault in each relay of the relay group; Step S600, when passing through all the fault detection phases, it is determined that there are no adhesion faults and closing faults in the relays in the relay group.

[0032] Similar to the prior art, before the grid-connected inverter starts, it is necessary to detect the adhesion faults and closing faults of each relay to ensure that each relay can work normally. The difference is that in the relay fault detection method of this application, the relays are divided into those controlled by the first controller and the second controller, and the detection is combined with the fourth relay K4, the fifth relay K5, and the sixth relay K6 on the neutral line, and there are certain requirements for the sequence of the fault detection process. During the detection process, the control actions of the second controller can be reduced. Only when it is necessary to control the relays responsible for the second controller, the first controller confirms the control situation of the second controller through communication, thereby reducing the detection duration and ensuring the reliability of the detection process.

[0033] Before the grid-connected inverter starts, the grid-connected inverter shuts down the output, and then five stages of fault detection are carried out. The first stage of fault detection is to disconnect all the relays. The first controller determines whether there are simultaneous adhesion faults in the main relays and auxiliary relays on each phase line according to the magnitude relationship between the voltage on the inverter side and the voltage on the grid side; the second stage of fault detection is to disconnect all the auxiliary relays. The first controller determines whether there is an adhesion fault in the auxiliary relays on each phase line according to the magnitude relationship between the voltage on the inverter side and the voltage on the grid side; the third stage of fault detection is to disconnect the relay on the neutral line one by one. The first controller determines whether there is an adhesion fault in the relay on the neutral line according to the magnitude relationship between the voltage on the inverter side and the voltage on the grid side; the fourth stage of fault detection is to disconnect all the main relays. The first controller determines whether there is an adhesion fault in the main relays on each phase line according to the magnitude relationship between the voltage on the inverter side and the voltage on the grid side; the fifth stage of fault detection is to only disconnect the fourth relay K4 and close the other relays. The first controller determines whether there is a closing fault in each relay according to the magnitude relationship between the voltage on the inverter side and the voltage on the grid side. After the above five stages of fault detection are completed, if it is judged that there are no adhesion faults and closing faults in the relays, it is considered that there are no adhesion faults and closing faults in the relays in the relay group, and the grid-connected inverter can enter the working state.

[0034] The fault detection for each stage will be described in detail below.

[0035] Referring to Figure 3 As shown, in some embodiments, the fault detection in the first stage: In step S100, all relays are disconnected to detect whether the main relays and auxiliary relays on each phase line are simultaneously stuck, including: Step S110, disconnect the main relays, the fourth relay K4, and the fifth relay K5 on each phase line, and instruct the second controller to disconnect the auxiliary relays and the sixth relay K6 on each phase line; Step S120, obtain the inverter-side voltage and grid-side voltage corresponding to each phase line; Step S130, when the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than the first threshold, it is determined that the main relay and the auxiliary relay on the corresponding phase line are simultaneously stuck.

[0036] When the output of the grid-connected inverter is turned off, the first controller controls the first main relay K11, the second main relay K21, and the third main relay K31 to disconnect, and also controls the fourth relay K4 and the fifth relay K5 to disconnect. The first controller communicates with the second controller to instruct the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32, and the sixth relay K6 to disconnect. At this time, all the relays in the relay group are disconnected, and the inverter-side voltage and grid-side voltage of the three phase lines are measured.

[0037] When the difference between the inverter-side voltage and the grid-side voltage of any phase line (for example, phase line L1) is less than the first threshold, it indicates that the main relay and the auxiliary relay on this phase line (if it is phase line L1, corresponding to the first main relay K11 and the first auxiliary relay K12) are both stuck. On this phase line, the grid is connected to the grid-connected inverter, so that the potential difference between the grid side and the inverter side is not large (judged by being less than the first threshold), then the system reports a fault, and the detection process can be terminated. If the difference between the inverter-side voltage and the grid-side voltage of any phase line is greater than the first threshold, it indicates that there is an open circuit on this phase line, that is, some relays are in the off state, and there is no situation where the main relay and the auxiliary relay are simultaneously stuck. Therefore, when the phase lines L1, L2, and L3 all meet the condition that the difference between the inverter-side voltage and the grid-side voltage is greater than the first threshold, it indicates that the fault detection in the first stage is passed.

[0038] It can be understood that for the control of the relays, in fact, the first controller sends disconnection commands or closing commands to the first main relay K11, the second main relay K21, the third main relay K31, the fourth relay K4, and the fifth relay K5, and the second controller sends disconnection commands or closing commands to the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32, and the sixth relay K6. However, whether each relay has been normally disconnected or normally closed after receiving the command needs to be determined by the first controller based on the magnitude relationship between the voltage on the inverter side and the voltage on the grid side.

[0039] Referring Figure 4 As shown, in some embodiments, the fault detection in the second stage: In step S200, the auxiliary relays are disconnected to detect whether there is an adhesion fault in the auxiliary relays on each phase line, including: Step S210, close all the main relays, the fourth relay K4, and the fifth relay K5, and instruct the second controller to close the sixth relay K6, and disconnect the first auxiliary relay K12, the second auxiliary relay K22, and the third auxiliary relay K32; Step S220, obtain the voltage on the inverter side and the voltage on the grid side corresponding to each phase line; Step S230, when the difference between the voltage on the inverter side and the voltage on the grid side of any phase line is less than the first threshold, it is determined that there is an adhesion fault in the auxiliary relay on the corresponding phase line.

[0040] If the fault detection in the first stage is passed, all the relays are instructed to be disconnected. After entering the second stage, the first controller controls the first main relay K11, the second main relay K21, and the third main relay K31 to close, and also controls the fourth relay K4 and the fifth relay K5 to close. The first controller communicates with the second controller to instruct the second controller to control the sixth relay K6 to close, and controls the first auxiliary relay K12, the second auxiliary relay K22, and the third auxiliary relay K32 to be disconnected. At this time, it is equivalent to that all the relays in the relay group except the three auxiliary relays are closed, and the voltage on the inverter side and the voltage on the grid side of the three phase lines are measured.

[0041] When the difference between the voltage on the inverter side and the grid side of any phase line (for example, the L1 phase line) is less than the first threshold, it indicates that the secondary relays on this phase line (if it is the L1 phase line, it is the first secondary relay K12) are all stuck. When the grid is connected to the grid-connected inverter on this phase line, the potential difference between the grid side and the inverter side is not large (judged by being less than the first threshold), then the system reports a fault and the detection process can be terminated; this judgment process actually excludes the case where the main relay on this phase line has a closed fault, because if the main relay has a closed fault, then this phase line is open, and there is no situation where the difference between the voltage on the inverter side and the grid side is less than the first threshold. If the difference between the voltage on the inverter side and the grid side of any phase line is greater than the first threshold, it indicates that there is an open circuit on this phase line, that is, some relays are in the off state. Therefore, when the L1 phase line, the L2 phase line, and the L3 phase line all meet the condition that the difference between the voltage on the inverter side and the grid side is greater than the first threshold, it indicates that the fault detection in the second stage passes. The second stage is used to detect whether the first secondary relay K12, the second secondary relay K22, and the third secondary relay K32 are stuck.

[0042] Referring to Figure 5 As shown, in some embodiments, the fault detection in the third stage: In step S300, the relay on the neutral line is disconnected to detect whether the relay on the neutral line is stuck, including: Step S310, close the first main relay K11, the fourth relay K4, and the fifth relay K5, open the second main relay K21 and the third main relay K31, and instruct the second controller to close each secondary relay and open the sixth relay K6; Step S320, obtain the voltage on the inverter side and the grid side of the L1 phase line; Step S330, when the difference between the voltage on the inverter side and the grid side of the L1 phase line is less than the first threshold, determine that the sixth relay K6 is stuck; Step S340, when the difference between the voltage on the inverter side and the grid side of the L1 phase line is greater than the first threshold, open the fifth relay K5 and instruct the second controller to close the sixth relay K6; Step S350, obtain the voltage on the inverter side and the grid side of the L1 phase line; Step S360, when the difference between the voltage on the inverter side and the grid side of the L1 phase line is less than the first threshold, determine that the fifth relay K5 is stuck; Step S370, when the difference between the voltage on the inverter side and the grid side of the L1 phase line is greater than the first threshold, open the fourth relay K4 and close the fifth relay K5; Step S380, obtain the voltage on the inverter side and the grid side of the L1 phase line; Step S390: When the difference between the voltage on the inverter side of the L1 phase line and the grid-side voltage is less than the first threshold, it is determined that the fourth relay K4 has a sticking fault.

[0043] If the fault detection in the second stage is passed, all the main relays and the three relays on the neutral line are instructed to close, and all the auxiliary relays are instructed to open. After entering the third stage, it is necessary to separately open the three relays on the neutral line in sequence, so there are three sub-stages.

[0044] The first sub-stage is to separately open the sixth relay K6. Specifically, the first controller controls the first main relay K11, the fourth relay K4, and the fifth relay K5 to close, controls the second main relay K21 and the third main relay K31 to open. The first controller communicates with the second controller and instructs the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, and the third auxiliary relay K32 to close, and controls the sixth relay K6 to open. At this time, it is equivalent to the main relay and the auxiliary relay on the L1 phase line being closed, the L2 phase line and the L3 phase line being open, and the neutral line being controlled to be open by the sixth relay K6. Measure the voltage on the inverter side and the grid-side voltage of the L1 phase line.

[0045] When the difference between the voltage on the inverter side and the grid-side voltage of the L1 phase line is less than the first threshold, it indicates that the L1 phase line is connected to the neutral line. Since the main relay and the auxiliary relay on the L1 phase line are both instructed to close, and the fourth relay K4 and the fifth relay K5 on the neutral line are both instructed to close, it is considered that the sixth relay K6 on the neutral line has a sticking fault, resulting in the connection between the L1 phase line and the neutral line, and the system reports a fault, and the detection process can be terminated; if the difference between the voltage on the inverter side and the grid-side voltage of the L1 phase line is greater than the first threshold, it indicates that there is an open circuit in the circuit connecting the L1 phase line and the neutral line, and it is considered that the sixth relay K6 can be normally opened without a sticking fault.

[0046] The second sub-stage is to separately open the fifth relay K5. Specifically, the first controller controls the first main relay K11 and the fourth relay K4 to close, controls the second main relay K21, the third main relay K31, and the fifth relay K5 to open. The first controller communicates with the second controller and instructs the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32, and the sixth relay K6 to close. At this time, it is equivalent to the main relay and the auxiliary relay on the L1 phase line being closed, the L2 phase line and the L3 phase line being open, and the neutral line being controlled to be open by the fifth relay K5. Measure the voltage on the inverter side and the grid-side voltage of the L1 phase line.

[0047] When the difference between the inverter-side voltage and the grid-side voltage on the L1 phase line is less than the first threshold, it indicates that the L1 phase line is connected to the neutral line. Since the main relay and the auxiliary relay on the L1 phase line are both indicated to be closed, and the fourth relay K4 and the sixth relay K6 on the neutral line are both indicated to be closed, it is considered that the fifth relay K5 on the neutral line has a sticking fault, resulting in the connection between the L1 phase line and the neutral line. The system reports a fault, and the detection process can be terminated. If the difference between the inverter-side voltage and the grid-side voltage on the L1 phase line is greater than the first threshold, it indicates that there is an open circuit in the circuit connecting the L1 phase line and the neutral line, and it is considered that the fifth relay K5 can be normally disconnected without a sticking fault.

[0048] The third sub-stage is to separately disconnect the fourth relay K4. Specifically, the first controller controls the first main relay K11 and the fifth relay K5 to be closed, controls the second main relay K21, the third main relay K31 and the fourth relay K4 to be disconnected. The first controller communicates with the second controller to instruct the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32 and the sixth relay K6 to be closed. At this time, it is equivalent to the main relay and the auxiliary relay on the L1 phase line being closed, the L2 phase line and the L3 phase line being open, and the neutral line being controlled to be open by the fourth relay K4. Measure the inverter-side voltage and the grid-side voltage of the L1 phase line.

[0049] When the difference between the inverter-side voltage and the grid-side voltage on the L1 phase line is less than the first threshold, it indicates that the L1 phase line is connected to the neutral line. Since the main relay and the auxiliary relay on the L1 phase line are both indicated to be closed, and the fifth relay K5 and the sixth relay K6 on the neutral line are both indicated to be closed, it is considered that the fourth relay K4 on the neutral line has a sticking fault, resulting in the connection between the L1 phase line and the neutral line. The system reports a fault, and the detection process can be terminated. If the difference between the inverter-side voltage and the grid-side voltage on the L1 phase line is greater than the first threshold, it indicates that there is an open circuit in the circuit connecting the L1 phase line and the neutral line, and it is considered that the fourth relay K4 can be normally disconnected without a sticking fault.

[0050] It should be noted that the above steps take the connection between the L1 phase line and the neutral line as an example for illustration. In fact, the connection between the L2 phase line or the L3 phase line and the neutral line can be selected, and the closing of the first main relay K11 can be changed to the closing of the second main relay K21 or the third main relay K31.

[0051] It should be noted that the order of the above first sub-stage, second sub-stage and third sub-stage can be interchanged. In fact, as long as the three relays on the neutral line are disconnected in turn to measure the sticking fault.

[0052] Refer to Figure 6As shown, in some embodiments, for the fault detection in the fourth stage: In step S400, the main relay is disconnected to detect whether there is an adhesion fault in the main relay on each phase line, including: Step S410, close the fourth relay K4 and the fifth relay K5, disconnect each main relay, and instruct the second controller to close each auxiliary relay and the sixth relay K6; Step S420, obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; Step S430, when the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than the first threshold, it is determined that there is an adhesion fault in the main relay on the corresponding phase line.

[0053] If the fault detection in the third stage is passed, one of the main relays is instructed to close, the other two main relays are instructed to open, each auxiliary relay is instructed to close, and two of the three relays on the neutral line are instructed to close, and the remaining one relay is instructed to open. After entering the fourth stage, the first controller controls the first main relay K11, the second main relay K21, and the third main relay K31 to open, and also controls the fourth relay K4 and the fifth relay K5 to close. The first controller communicates with the second controller and instructs the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32, and the sixth relay K6 to close. At this time, it is equivalent to that all the remaining relays in the relay group are closed except the three main relays, and the inverter-side voltage and the grid-side voltage of the three phase lines are measured.

[0054] When the difference between the inverter-side voltage and the grid-side voltage on any phase line (for example, phase line L1) is less than the first threshold, it indicates that the main relay on this phase line (if it is phase line L1, it is the first main relay K11) has an adhesion fault, and the grid is connected to the grid-connected inverter on this phase line, so that the potential difference between the grid side and the inverter side is not large (judged by less than the first threshold), then the system reports a fault and the detection process can be terminated; this judgment process actually excludes the case of a closed fault in the auxiliary relay on this phase line, because if the auxiliary relay has a closed fault, then this phase line is open, and there is no case where the difference between the inverter-side voltage and the grid-side voltage is less than the first threshold. If the difference between the inverter-side voltage and the grid-side voltage on any phase line is greater than the first threshold, it indicates that there is an open circuit on this phase line, that is, there is a relay in the open state. Therefore, when the phase lines L1, L2, and L3 all meet the condition that the difference between the inverter-side voltage and the grid-side voltage is greater than the first threshold, it indicates that the fault detection in the fourth stage is passed. The fourth stage is used to detect whether the first main relay K11, the second main relay K21, and the third main relay K31 have adhesion faults.

[0055] Through the above fault detection process from the first stage to the fourth stage, the adhesion faults of all relays can be measured. However, there are cases where the relays have closing faults. For example, in the second stage, although it can be determined that the difference between the inverter-side voltage and the grid-side voltage of a certain phase line is greater than the first threshold, there may be a phenomenon that the main relay of this phase line has a closing fault while the auxiliary relay has no adhesion fault, or the main relay of this phase line has a closing fault while the auxiliary relay has an adhesion fault, etc. Therefore, in the fifth stage, it is necessary to detect the closing faults of the relays.

[0056] Referring to Figure 7 As shown, in some embodiments, the fault detection in the fifth stage: In step S500, the fourth relay K4 is disconnected to detect whether there are closing faults in each relay of the relay group, including: Step S510, close each main relay and the fifth relay K5, disconnect the fourth relay K4, and instruct the second controller to close each auxiliary relay and the sixth relay K6; Step S520, obtain the inverter-side voltage and the grid-side voltage corresponding to each phase line; Step S530, when the difference between the inverter-side voltage and the grid-side voltage of any phase line is greater than the second threshold, determine that the main relay on the corresponding phase line has an adhesion fault.

[0057] After entering the fifth stage, the first controller controls the first main relay K11, the second main relay K21, the third main relay K31, and the fifth relay K5 to close, and also controls the fourth relay K4 to disconnect. The first controller communicates with the second controller and instructs the second controller to control the first auxiliary relay K12, the second auxiliary relay K22, the third auxiliary relay K32, and the sixth relay K6 to close. At this time, it is equivalent to that except for the fourth relay K4, the rest of the relays in the relay group are closed, and the inverter-side voltage and the grid-side voltage of the three phase lines are measured.

[0058] When the difference between the voltage on the inverter side and the grid side on any phase line (for example, the L1 phase line) is greater than the second threshold, it indicates that at least one relay on this phase line (if it is the L1 phase line, it is the first main relay K11 and / or the second main relay K21) has a closing fault, and the grid is disconnected from the grid-connected inverter on this phase line, resulting in a large difference between the grid side potential and the inverter side potential (judged by being greater than the second threshold), then the system reports a fault and the detection process can be terminated. The above judgment process can eliminate some omitted problems in the first four stages. For example, if there may be a closing fault of the main relay on this phase line but no adhesion fault of the auxiliary relay in the second stage, the fifth stage can judge the relay with the actual closing fault on this phase line, thus avoiding the fault detection loophole. If the difference between the voltage on the inverter side and the grid side on any phase line is less than the second threshold, it indicates that there is no open circuit on this phase line, and both the main relay and the auxiliary relay are in the closed state. Therefore, when the L1 phase line, the L2 phase line, and the L3 phase line all meet the condition that the difference between the voltage on the inverter side and the grid side is less than the second threshold, it indicates that the fault detection in the fifth stage passes.

[0059] So far, the fault detection in the five stages has been completed. Finally, at the end of the fifth stage, only the fourth relay K4 in the relay group is in the open state. If the grid-connected inverter needs to enter the off-grid mode next, only control the fourth relay K4 to close and switch to the corresponding working state for off-grid. If the grid-connected inverter needs to enter the grid-connected mode next, it can switch to the corresponding working state for grid connection.

[0060] The relay fault detection method of the present application will be described in detail below through a specific example.

[0061] There are 9 relays between the grid-connected inverter and the grid. There are two relays (main relay and auxiliary relay) on each of the three-phase live wires, and three relays on the neutral wire. Among them, the relays K4, K11, K21, K31, and K5 are controlled by the first controller, and the relays K12, K22, K32, and K6 are controlled by the second controller. The first controller respectively collects the grid side voltage and the inverter side voltage, and controls the entire relay group fault detection process accordingly.

[0062] Under the control of the first controller, the DC-AC grid-connected inverter and the relays perform the following actions in sequence: Step (1) First, disconnect all relays and turn off the inverter output. In this state, respectively judge the difference between the inverter side voltage and the grid side voltage of each phase. If the difference between the two on a certain phase is less than threshold 1, it means that there is an adhesion fault of the relay on this phase, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step; Step (2): Close relays K4, K11, K21, K31, K5, and K6, and open relays K12, K22, and K32. In this state, after communicating with the second controller to confirm that relay K6 is closed, respectively judge the difference between the inverter-side voltage and the grid-side voltage of each phase. If the difference between the two of a certain phase is less than threshold 1, it indicates that the relay of this phase has an adhesion fault, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step. This step is used to detect whether relays K12, K22, and K32 are adhered; Step (3): Close relays K4, K11, K5, K12, K22, and K32, and open relays K21, K31, and K6. In this state, after communicating with the second controller to confirm that relay K6 is open and relays K12, K22, and K32 are closed, respectively judge the difference between the inverter-side voltage and the grid voltage of each phase. If the difference between the two of a certain phase is less than threshold 1, it indicates that the relay of this phase has an adhesion fault, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step. This step is used to detect whether relay K6 is adhered; Step (4): Close relays K4, K11, K12, K22, K32, and K6, and open relays K21, K31, and K5. In this state, after communicating with the second controller to confirm that relay K6 is closed, respectively judge the difference between the inverter-side voltage and the grid voltage of each phase. If the difference between the two of a certain phase is less than threshold 1, it indicates that the relay of this phase has an adhesion fault, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step. This step is used to detect whether relay K5 is adhered; Step (5): Close relays K11, K5, K12, K22, K32, and K6, and open relays K4, K21, and K31. In this state, respectively judge the difference between the inverter-side voltage and the grid voltage of each phase. If the difference between the two of a certain phase is less than threshold 1, it indicates that the relay of this phase has an adhesion fault, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step. This step is used to detect whether relay K4 is adhered; Step (6): Close relays K4, K5, K12, K22, K32, and K6, and open relays K11, K21, and K31. In this state, respectively judge the difference between the inverter-side voltage and the grid voltage of each phase. If the difference between the two of a certain phase is less than threshold 1, it indicates that the relay of this phase has an adhesion fault, the system reports a fault, and exits the detection process. If the differences between the two are all greater than threshold 1, continue to the next step. This step is used to detect whether relays K11, K21, and K31 are adhered; Step (7): Close relays K11, K21, K31, K5, K12, K22, K32, and K6, and open relay K4. In this state, respectively judge the difference between the inverter-side voltage of each phase and the grid voltage. If the difference between the two for a certain phase is greater than the threshold value 2, it indicates that there is a closing fault in the relay of this phase, the system reports a fault, and the detection process exits. If the differences between the two are all less than the threshold value 2, continue to run. This step is used to detect whether each relay cannot be closed; During the whole process, the adhesion of any single or multiple relays can be detected, and the fault that the relay cannot be closed can also be detected. In addition, during the whole detection process, the actions of the four relays controlled by the second controller are minimized as much as possible, and if there are actions of these four relays, the action conditions of the relays are confirmed through communication, thereby reducing the detection duration and ensuring the reliability of the detection process.

[0063] As Figure 8 shown, Figure 8 is a schematic diagram of the controller 1000 provided by an embodiment of the present application.

[0064] The embodiment of the present application also provides a controller 1000, including at least one processor and a memory for communicating with the at least one processor; the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the control method as described in the above embodiment.

[0065] The controller 1000 of the embodiment of the present application includes one or more processors 1001 and a memory 1002, Figure 8 taking one processor 1001 and one memory 1002 as an example.

[0066] The processor 1001 and the memory 1002 can be connected through a bus or other means, Figure 8 taking the connection through a bus as an example.

[0067] The memory 1002, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. In addition, the memory 1002 can include high-speed random access memory, and can also include non-transitory memory, such as at least one disk storage device, a flash memory device, or other non-transitory solid-state storage devices. In some embodiments, the memory 1002 may optionally include a memory 1002 remotely set relative to the processor 1001, and these remote memories can be connected to the controller 1000 through a network. Examples of the above network include but are not limited to the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0068] An embodiment of the present application also provides a grid-connected system, including a controller 1000. The controller 1000 is used to execute the foregoing fault detection method.

[0069] Those of ordinary skill in the art will understand that all or some of the steps and systems disclosed in the above methods can be implemented as software, firmware, hardware, and appropriate combinations thereof. Some or all of the physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, as is well known to those of ordinary skill in the art, communication media typically includes computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0070] The above is a specific description of the preferred embodiment of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A relay fault detection circuit for a grid-connected inverter, wherein the grid-connected inverter is connected to the power grid with an L1 phase line, an L2 phase line, an L3 phase line and a neutral line, characterized in that: The fault detection circuit comprises: a relay group, comprising a first main relay and a first sub-relay connected in sequence to the L1 phase line, a second main relay and a second sub-relay connected in sequence to the L2 phase line, a third main relay and a third sub-relay connected in sequence to the L3 phase line, and a fourth relay, a fifth relay and a sixth relay connected in sequence to the neutral line; An inverter side voltage detection module, used to collect the inverter side voltage; A grid-side voltage detection module, used to collect grid-side voltage; a first controller, used for controlling the opening and closing of each main relay, the fourth relay and the fifth relay, and also used for obtaining the inverter side voltage through the inverter side voltage detection module and obtaining the grid side voltage through the grid side voltage detection module; The second controller is communicatively connected with the first controller and is used for controlling the opening and closing of each auxiliary relay and the sixth relay.

2. A relay fault detection method for a grid-connected inverter, characterized in that: The first controller applied to the relay fault detection circuit according to claim 1, wherein the fault detection method comprises: Before the grid-connected inverter is started, it cooperates with the second controller to perform fault detection in the following stages in sequence: Disconnect all relays to detect whether the main relays and auxiliary relays on each phase line have adhesion faults at the same time; Disconnect the auxiliary relay to detect whether the auxiliary relay on each phase line has a sticking fault; Disconnecting the relay on the neutral line to detect whether the relay on the neutral line has a sticking fault; Disconnect the main relay to detect whether the main relay on each phase line has a sticking fault; Disconnecting the fourth relay to detect whether each relay of the relay group has a closing fault; After passing all the fault detection stages, it is determined that the relays in the relay group have no sticking faults and closing faults.

3. The fault detection method according to claim 2, characterized in that: The method of disconnecting all relays to detect whether the main relays and the auxiliary relays on each phase line have adhesion faults at the same time includes: Disconnecting the main relay, the fourth relay and the fifth relay on each phase line, and instructing the second controller to disconnect the auxiliary relay and the sixth relay on each phase line; Obtaining the inverter side voltage and the grid side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than a first threshold, it is determined that the main relay and the auxiliary relay on the corresponding phase line simultaneously have adhesion faults.

4. The fault detection method according to claim 2, characterized in that: The disconnecting of the auxiliary relays to detect whether the auxiliary relays on each phase line have a sticking fault includes: closing each main relay, the fourth relay and the fifth relay, and instructing the second controller to close the sixth relay and disconnect the first sub-relay, the second sub-relay and the third sub-relay; Obtaining the inverter side voltage and the grid side voltage corresponding to each phase line; When the difference between the inverter side voltage and the grid side voltage of any phase line is less than a first threshold, it is determined that a sticking fault occurs in the auxiliary relay on the corresponding phase line.

5. The fault detection method according to claim 4, characterized in that: The disconnecting the relay on the neutral line to detect whether the relay on the neutral line has a sticking fault includes: closing the first main relay, the fourth relay and the fifth relay, opening the second main relay and the third main relay, and instructing the second controller to close each sub-relay and open the sixth relay; Acquire the inverter side voltage and the grid side voltage of the L1 phase line; When the difference between the inverter side voltage and the grid side voltage of the L1 phase line is less than a first threshold, determining that a sticking fault occurs in the sixth relay; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is greater than a first threshold, disconnecting the fifth relay and instructing the second controller to close the sixth relay; Acquire the inverter side voltage and the grid side voltage of the L1 phase line; When the difference between the inverter side voltage and the grid side voltage of the L1 phase line is less than a first threshold, determining that a sticking fault occurs to the fifth relay; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is greater than a first threshold, disconnecting the fourth relay and closing the fifth relay; Acquire the inverter side voltage and the grid side voltage of the L1 phase line; When the difference between the inverter-side voltage and the grid-side voltage of the L1 phase line is less than a first threshold, it is determined that a sticking fault occurs in the fourth relay.

6. The fault detection method according to claim 5, characterized in that: The disconnecting of the main relay to detect whether the main relays on each phase line have a sticking fault comprises: closing the fourth relay and the fifth relay, opening each main relay, and instructing the second controller to close each sub relay and the sixth relay; Obtaining the inverter side voltage and the grid side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is less than a first threshold, it is determined that a sticking fault occurs in the main relay on the corresponding phase line.

7. The fault detection method according to claim 6, characterized in that: The step of disconnecting the fourth relay to detect whether each relay of the relay group has a closing fault comprises: closing each main relay and the fifth relay, opening the fourth relay, and instructing the second controller to close each sub relay and the sixth relay; Obtaining the inverter side voltage and the grid side voltage corresponding to each phase line; When the difference between the inverter-side voltage and the grid-side voltage of any phase line is greater than a second threshold, it is determined that a sticking fault occurs in the main relay on the corresponding phase line.

8. The fault detection method according to claim 1, characterized in that: The fault detection method further comprises: When a fault is detected during any stage of the fault detection process, the fault detection process is exited and a fault prompt is issued.

9. A controller, characterized in that: comprising at least one processor and a memory for communicatively connecting to the at least one processor; The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the fault detection method according to any one of claims 2 to 8.

10. A grid-connected system, characterized in that: Comprising a controller as claimed in claim 9.

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