Control method and control circuit

Abstract

The application discloses a control method and a control circuit, the control method comprising controlling a first relay, a second relay, a third relay and a fourth relay to be closed; acquiring a first inverter voltage and a first grid voltage; controlling the first relay to be opened, acquiring a first measurement value and a second inverter voltage; controlling the second relay to be opened, acquiring a second measurement value and a second grid voltage; controlling the third relay to be opened, acquiring a third measurement value and a third inverter voltage; controlling the fourth relay to be opened, acquiring a fourth measurement value and a third grid voltage; and judging whether the first relay, the second relay, the third relay and the fourth relay are failed according to the first inverter voltage, the first grid voltage, the first measurement value, the second inverter voltage, the second measurement value, the second grid voltage, the third measurement value, the third inverter voltage, the fourth measurement value and the third grid voltage. The control method provided by the application can accurately judge the failed relay.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and more specifically, to a control method and control circuit. Background Technology

[0002] To meet safety regulations, the inverter needs to be connected to the power grid's live wire via two relays connected in series, and to the power grid's neutral wire via two relays connected in series. The controller controls the on / off state of the four relays to control the inverter's connection or disconnection from the power grid. However, when a circuit fault occurs, because all four relays are controlled by the controller, it is impossible to detect which specific relay is faulty by controlling the on / off state of the relays, increasing maintenance difficulty and costs. Summary of the Invention

[0003] This application provides a control method and control circuit to solve at least one of the above-mentioned technical problems.

[0004] The control method of this application is used to control the connection circuit between an inverter and the power grid. The connection circuit includes a first relay, a second relay, a third relay, and a fourth relay. The first relay and the second relay are connected in series to the positive terminal of the inverter and the live wire of the power grid. The third relay and the fourth relay are connected in series to the negative terminal of the inverter and the neutral wire of the power grid. The control method includes:

[0005] Control the closure of the first relay, the second relay, the third relay, and the fourth relay;

[0006] Obtain the first inverter voltage and the first grid voltage;

[0007] The first relay is disconnected, while the second, third, and fourth relays are closed.

[0008] The first measured value of the intermediate voltage and the second inverter voltage are obtained. The connection point of the first relay and the second relay is the first connection point, the connection point of the third relay and the fourth relay is the second connection point, and the intermediate voltage is the voltage between the first connection point and the second connection point.

[0009] The second relay is disconnected, while the first relay, the third relay, and the fourth relay are closed;

[0010] Obtain a second measured value of the intermediate voltage and a second grid voltage;

[0011] The third relay is disconnected, while the first, second, and fourth relays are closed.

[0012] Obtain the third measured value of the intermediate voltage and the third inverter voltage;

[0013] The fourth relay is disconnected, while the first, second, and third relays are closed.

[0014] Obtain the fourth measured value of the intermediate voltage and the third grid voltage;

[0015] Based on the first inverter voltage, the first grid voltage, the first measured value, the second inverter voltage, the second measured value, the second grid voltage, the third measured value, the third inverter voltage, the fourth measured value, and the third grid voltage, determine whether the first relay, the second relay, the third relay, and the fourth relay are faulty.

[0016] The control method provided in this application measures the inverter, the power grid, and the intermediate voltage when the first, second, third, and fourth relays are individually turned off. It can also accurately determine which relay has failed based on the voltage at the inverter, the power grid, and the intermediate point, which helps to reduce maintenance difficulty and cost.

[0017] In some embodiments, determining whether the first relay, the second relay, the third relay, and the fourth relay have failed includes:

[0018] When the difference between the first inverter voltage and the first grid voltage is less than a preset value, it is confirmed that the first relay, the second relay, the third relay and the fourth relay have not failed.

[0019] When the difference between the first inverter voltage and the first grid voltage is greater than or equal to a preset value, it is confirmed that at least one of the first relay, the second relay, the third relay and the fourth relay has failed.

[0020] In this way, the presence of relay failure can be detected as a whole, thereby determining whether further confirmation is needed, which helps save testing time.

[0021] In some embodiments, determining whether the first relay, the second relay, the third relay, and the fourth relay have failed includes:

[0022] When the difference between the first measured value and the second inverter voltage is less than a preset value, the first relay is confirmed to be faulty;

[0023] When the difference between the first measured value and the second inverter voltage is greater than or equal to a preset value, the first relay is confirmed to be normal.

[0024] In this way, it is possible to accurately determine whether the first relay has failed, which is beneficial for precise maintenance and replacement of the connecting circuit.

[0025] In some embodiments, determining whether the first relay, the second relay, the third relay, and the fourth relay have failed includes:

[0026] When the difference between the second measured value and the second mains voltage is less than a preset value, the second relay is confirmed to be faulty;

[0027] When the difference between the second measured value and the second mains voltage is greater than or equal to a preset value, the second relay is confirmed to be normal.

[0028] In this way, it is possible to accurately determine whether the second relay has failed, which is beneficial for precise maintenance and replacement of the connection circuit.

[0029] In some embodiments, determining whether the first relay, the second relay, the third relay, and the fourth relay have failed includes:

[0030] When the difference between the third measured value and the third inverter voltage is less than a preset value, the third relay is confirmed to be faulty.

[0031] When the difference between the third measured value and the third inverter voltage is greater than or equal to a preset value, the third relay is confirmed to be normal.

[0032] In this way, it is possible to accurately determine whether the third relay has failed, which is beneficial for precise maintenance and replacement of the connection circuit.

[0033] In some embodiments, determining whether the first relay, the second relay, the third relay, and the fourth relay have failed includes:

[0034] When the difference between the fourth measured value and the third mains voltage is less than a preset value, the fourth relay is confirmed to be faulty;

[0035] When the difference between the fourth measured value and the third mains voltage is greater than or equal to a preset value, the fourth relay is confirmed to be normal.

[0036] In this way, it is possible to accurately determine whether the fourth relay has failed, which is beneficial for precise maintenance and replacement of the connection circuit.

[0037] Another embodiment of the control circuit of this application is used to control the connection circuit between the inverter and the power grid. The connection circuit includes a first relay, a second relay, a third relay, and a fourth relay. The first relay and the second relay are connected in series to the positive terminal of the inverter and the live wire of the power grid. The third relay and the fourth relay are connected in series to the negative terminal of the inverter and the neutral wire of the power grid. The control circuit includes:

[0038] A first voltage acquisition module is connected at one end to the first relay and at the other end to the third relay. The first voltage acquisition module is used to acquire inverter voltage.

[0039] The second voltage acquisition module has one end connected to the first relay and the second relay, and the other end connected to the third relay and the fourth relay. The second voltage acquisition module is used to acquire intermediate voltage. The connection point between the first relay and the second relay is the first connection point, and the connection point between the third relay and the fourth relay is the second connection point. The intermediate voltage is the voltage between the first connection point and the second connection point.

[0040] The third voltage acquisition module is connected at one end to the second relay and at the other end to the fourth relay. The third voltage acquisition module is used to acquire the grid voltage.

[0041] The control module is configured to control the on / off state of the first relay, the second relay, the third relay, and the fourth relay, and to determine whether the first relay, the second relay, the third relay, and the fourth relay are faulty based on the inverter voltage, the intermediate voltage, and the grid voltage.

[0042] In this way, the control circuit can accurately identify the faulty relay, which helps to reduce the difficulty and cost of maintenance.

[0043] In some embodiments, the control module includes a first controller and a second controller. The first controller is connected to the first relay and the third relay respectively and is used to control the on / off state of the first relay and the third relay. The second controller is connected to the second relay and the fourth relay respectively and is used to control the on / off state of the second controller and the second relay.

[0044] In this way, if either the first controller or the second controller fails, the other controller can still disconnect the connection circuit, which helps to improve the safety of the connection circuit and avoid accidents.

[0045] In some embodiments, the control circuit further includes a drive circuit. The first relay includes a first coil. The drive circuit includes a first transistor, a second transistor, a first diode, and a first capacitor. The first diode is connected to a power supply. The cathode of the first diode is connected to a first end of the first coil. The second end of the first coil is connected to the collector of the second transistor. The emitter of the second transistor is grounded. The anode of the first capacitor is connected to the first end of the first coil. The cathode of the first capacitor is grounded. The emitter of the first transistor is connected to the power supply. The collector of the first transistor is connected to the cathode of the first capacitor. The base of the first transistor is connected to the collector of the second transistor. The base of the second transistor is connected to the control module.

[0046] In this way, only a lower voltage is needed to activate the first relay, which helps reduce the power consumption and heat generation of the first relay, and thus extends its service life.

[0047] In some embodiments, the driving circuit further includes a second diode and a first resistor, wherein the anode of the second diode is connected to a second end of the first coil, the cathode of the second diode is connected to one end of the first resistor, and the other end of the first resistor is connected to a first end of the first coil.

[0048] This is used to absorb the voltage spike generated by the first coil when the first relay is turned off, preventing the second transistor from being damaged.

[0049] Additional aspects and advantages of embodiments of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of this application. Attached Figure Description

[0050] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein:

[0051] Figure 1 This is a flowchart illustrating the control method according to an embodiment of this application;

[0052] Figure 2 This is a flowchart illustrating the control method according to an embodiment of this application;

[0053] Figure 3 This is a flowchart illustrating the control method according to an embodiment of this application;

[0054] Figure 4 This is a flowchart illustrating the control method according to an embodiment of this application;

[0055] Figure 5This is a flowchart illustrating the control method according to an embodiment of this application;

[0056] Figure 6 This is a flowchart illustrating the control method according to an embodiment of this application;

[0057] Figure 7 This is a circuit diagram of the control circuit and connection circuit of the embodiment of this application;

[0058] Figure 8 This is a circuit diagram of the control circuit and connection circuit of the embodiment of this application;

[0059] Figure 9 This is a circuit diagram of the driving circuit according to an embodiment of this application.

[0060] Key component symbols: Control circuit 100, first voltage acquisition module 10, second voltage acquisition module 20, third voltage acquisition module 30, control module 40, first controller 41, second controller 42, drive circuit 50, first transistor 501, second transistor 502, first diode 503, first capacitor 504, second diode 505, first resistor 506, second resistor 507, third resistor 508, fourth resistor 509, fifth resistor 510, sixth resistor 511, second capacitor 512, connection circuit 200, inverter 210, power grid 220, first relay 230, first coil 231, second relay 240, third relay 250, fourth relay 260, first connection point 270, second connection point 280. Detailed Implementation

[0061] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention. In the description of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection. They can refer to a mechanical connection or an electrical connection. They can refer to a direct connection or an indirect connection through an intermediate medium, and they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0063] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0064] This disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described herein. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0065] To meet safety regulations, the inverter needs to be connected to the live wire of the power grid via two relays connected in series, and to the neutral wire via two relays connected in series. By connecting four relays in pairs, additional electrical isolation is added between the inverter's DC terminal and the AC power grid, thereby improving system safety and helping to prevent current from flowing directly from the inverter into the grid, reducing the risk of electrical short circuits and faults. Furthermore, using relays in series provides additional redundancy protection. If one relay fails, the other relays can remain connected, ensuring continuous system operation and improving system reliability and stability, especially in applications requiring a highly reliable power supply.

[0066] Furthermore, the controller controls the on / off state of four relays to control the connection or disconnection of the inverter from the power grid. Using four relays connected in pairs allows for convenient control of the connection status between the inverter and the grid. By controlling the switching states of the relays, precise control of the inverter output can be achieved, thereby meeting the power grid's requirements for power quality and stability.

[0067] However, when a circuit malfunctions, since all four relays are controlled by the controller, it is impossible to detect which specific relay is faulty by controlling the on / off state of the relays through the controller. This increases the difficulty and cost of maintenance.

[0068] Please see Figure 1 The control method of this application is used to control the connection circuit 200 between the inverter 210 and the power grid 220. The connection circuit 200 includes a first relay 230, a second relay 240, a third relay 250, and a fourth relay 260. The first relay 230 and the second relay 240 are connected in series to the positive terminal of the inverter 210 and the live wire of the power grid 220. The third relay 250 and the fourth relay 260 are connected in series to the negative terminal of the inverter 210 and the neutral wire of the power grid 220. The control method includes:

[0069] Step 001: Control the closing of the first relay, the second relay, the third relay, and the fourth relay;

[0070] Step 002: Obtain the first inverter voltage and the first grid voltage;

[0071] Step 003: Control the first relay to open, and the second, third, and fourth relays to close;

[0072] Step 004: Obtain the first measured value of the intermediate voltage and the second inverter voltage. The connection point of the first relay and the second relay is the first connection point, the connection point of the third relay and the fourth relay is the second connection point, and the intermediate voltage is the voltage between the first connection point and the second connection point.

[0073] Step 005: Control the second relay to open, and the first, third, and fourth relays to close;

[0074] Step 006: Obtain the second measured value of the intermediate voltage and the second grid voltage;

[0075] Step 007: Control the third relay to open, and the first, second, and fourth relays to close;

[0076] Step 008: Obtain the third measured value of the intermediate voltage and the third inverter voltage;

[0077] Step 009: Control the fourth relay to open, and the first, second, and third relays to close;

[0078] Step 010: Obtain the fourth measured value of the intermediate voltage and the third grid voltage;

[0079] Step 011: Determine whether the first, second, third, and fourth relays are faulty based on the first inverter voltage, the first grid voltage, the first measured value, the second inverter voltage, the second measured value, the second grid voltage, the third measured value, the third inverter voltage, the fourth measured value, and the third grid voltage.

[0080] The control method provided in this application measures the inverter 210, the power grid 220, and the intermediate voltage when the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260 are individually turned off. It can also accurately determine which relay has failed based on the voltage at the midpoint of the inverter 210, the power grid 220, and the intermediate point, which helps to reduce maintenance difficulty and cost.

[0081] In some embodiments, steps 001 to 011 can be implemented by the control module 40, or in other words, the control module 40 can be used to control the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260 to close; obtain the first inverter voltage and the first grid voltage; it can also be used to control the first relay 230 to open and the second relay 240, the third relay 250, and the fourth relay 260 to close; obtain the first measured value of the intermediate voltage and the second inverter voltage between the connection point of the first relay 230 and the second relay 240 and the connection point of the third relay 250 and the fourth relay 260; it can also be used to control the second relay 240 to open and the first relay 230, the third relay 250, and the fourth relay 260 to close; obtain the intermediate voltage. The second measured value and the second grid voltage; it can also be used to control the third relay 250 to open and the first relay 230, the second relay 240 and the fourth relay 260 to close; to obtain the third measured value of the intermediate voltage and the third inverter voltage; it can also be used to control the fourth relay 260 to open and the first relay 230, the second relay 240 and the third relay 250 to close; to obtain the fourth measured value of the intermediate voltage and the third grid voltage; it can also be used to determine whether the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260 are faulty based on the first inverter voltage, the first grid voltage, the first measured value, the second inverter voltage, the second measured value, the second grid voltage, the third measured value, the third inverter voltage, the fourth measured value and the third grid voltage.

[0082] Specifically, the main functions of a relay are automatic control, automatic adjustment, automatic protection, and circuit switching. If a relay fails, these functions may not be possible, leading to circuit control failure. In complex circuit systems, the failure of one relay can trigger a chain reaction, causing the entire system to malfunction. As a crucial component of circuit control, the stability of a relay's performance directly affects the safe operation of the entire circuit system. When a relay fails to perform its intended circuit switching or adjustment functions for some reason, it is considered a relay failure.

[0083] Please see Figure 2 In some embodiments, step 011 includes:

[0084] 1101: When the difference between the voltage of the first inverter and the voltage of the first grid is less than a preset value, confirm that the first relay, the second relay, the third relay and the fourth relay are not malfunctioning;

[0085] 1102: When the difference between the voltage of the first inverter and the voltage of the first grid is greater than or equal to a preset value, confirm that at least one of the first relay, the second relay, the third relay and the fourth relay has failed.

[0086] In this way, the presence of relay failure can be detected as a whole, thereby determining whether further confirmation is needed, which helps save testing time.

[0087] In some embodiments, sub-steps 1101 and 1102 can be implemented by the control module 40. In other words, the control module 40 can be used to confirm that the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260 are all functioning correctly when the difference between the first inverter voltage and the first grid voltage is less than a preset value; and to confirm that at least one of the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260 is functioning correctly when the difference between the first inverter voltage and the first grid voltage is greater than or equal to a preset value.

[0088] Specifically, in this embodiment, when a fault occurs in the connection circuit 200, before performing specific relay failure detection, it is first necessary to check whether a relay has failed, that is, to determine whether the fault is caused by a relay. The specific operation method is as follows:

[0089] The first controller 41 and the second controller 42 simultaneously send drive signals to close the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260, and determine the first inverter voltage V transmitted back from the first voltage acquisition module 10. local_1 The first grid voltage V transmitted back from the third voltage acquisition module 30 Grid_1 Is the difference less than the preset value V? th That is, |V Grid_1 -Vlocal_1 | < V th Is the condition met? If it is met, then it is determined that the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260 can all close normally, and the next step of testing can be performed; otherwise, it is determined that the relay closure is ineffective, and the test ends.

[0090] Furthermore, the preset value V th In this embodiment of the application, the preset value V is a fixed value set based on experience. th It is 3V.

[0091] Please see Figure 3 In some embodiments, step 011 includes:

[0092] 1103: When the difference between the first measured value and the second inverter voltage is less than the preset value, the first relay is confirmed to be faulty;

[0093] 1104: When the difference between the first measured value and the second inverter voltage is greater than or equal to the preset value, the first relay is confirmed to be normal.

[0094] In this way, it is possible to accurately determine whether the first relay 230 has failed, which is beneficial for the precise maintenance and replacement of the connection circuit 200.

[0095] In some embodiments, sub-steps 1103 and 1104 can be implemented by the control module 40, or the control module 40 can be used to confirm that the first relay 230 is faulty when the difference between the first measured value and the second inverter voltage is less than a preset value; and to confirm that the first relay 230 is normal when the difference between the first measured value and the second inverter voltage is greater than or equal to the preset value.

[0096] Specifically, in this embodiment, after determining that a relay is faulty, the usage of the four relays is screened sequentially. First, it is determined whether the first relay 230 is faulty. The specific operation method is as follows:

[0097] The first controller 41 controls the third relay 250 to close and the first relay 230 to open. The second controller 42 controls the second relay 240 and the fourth relay 260 to close, and determines the first measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_1 The second inverter voltage V transmitted back from the first voltage acquisition module 10 local_2 Is the difference less than the preset value V? th That is, |V mid_1 -V local_2 | < V th If the condition is met, the first relay 230 is deemed to have failed to disconnect, and the test ends. Otherwise, the first relay 230 is deemed to have disconnected normally, and the next test is performed.

[0098] Please see Figure 4 In some embodiments, step 011 includes:

[0099] 1105: When the difference between the second measured value and the second mains voltage is less than the preset value, the second relay is confirmed to be faulty;

[0100] 1106: When the difference between the second measured value and the second mains voltage is greater than or equal to the preset value, the second relay is confirmed to be normal.

[0101] In this way, it is possible to accurately determine whether the second relay 240 has failed, which is beneficial for the precise maintenance and replacement of the connection circuit 200.

[0102] In some embodiments, sub-steps 1105 and 1106 can be implemented by the control module 40, or the control module 40 can be used to confirm that the second relay 240 is faulty when the difference between the second measured value and the second grid voltage is less than a preset value; and to confirm that the second relay 240 is normal when the difference between the second measured value and the second grid voltage is greater than or equal to the preset value.

[0103] Specifically, in this embodiment, when no problem is found with the first relay 230, it is determined whether the second relay 240 has failed. The specific operation method is as follows:

[0104] Furthermore, the first controller 41 controls the closing of the first relay 230 and the third relay 250, while the second controller 42 controls the closing of the fourth relay 260 and the opening of the second relay 240, and determines the second measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_2 The second grid voltage V transmitted back from the third voltage acquisition module 30 Grid_2 Is the difference less than the preset value V? th That is, |V Grid_2 –V mid_2 | < V th If the condition is met, the second relay 240 is deemed to have failed to disconnect, and the test ends. Otherwise, the second relay 240 is deemed to have disconnected normally, and the next test is performed.

[0105] Please see Figure 5 In some embodiments, step 011 includes:

[0106] 1107: When the difference between the third measured value and the third inverter voltage is less than the preset value, the third relay is confirmed to be faulty;

[0107] 1108: When the difference between the third measured value and the third inverter voltage is greater than or equal to the preset value, the third relay is confirmed to be normal.

[0108] In this way, it is possible to accurately determine whether the third relay 250 has failed, which is beneficial for the precise maintenance and replacement of the connection circuit 200.

[0109] In some embodiments, sub-steps 1107 and 1108 can be implemented by the control module 40, or the control module 40 can be used to confirm that the third relay 250 is faulty when the difference between the third measured value and the second inverter voltage is less than a preset value; and to confirm that the third relay 250 is normal when the difference between the third measured value and the second inverter voltage is greater than or equal to the preset value.

[0110] Specifically, in this embodiment, when no problem is found with the second relay 240, it is determined whether the third relay 250 has failed. The specific operation method is as follows:

[0111] Furthermore, the first controller 41 controls the closing of the first relay 230 and the opening of the third relay 250, while the second controller 42 controls the closing of the second relay 240 and the fourth relay 260, and determines the third measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_3 The third inverter voltage V transmitted back from the first voltage acquisition module 10 local_3 Is the difference less than the preset value V? th That is, |V mid_3 -V local_3 | < V th If the condition is met, the third relay 250 is deemed to have failed to disconnect, and the test ends. Otherwise, the third relay 250 is deemed to have disconnected normally, and the next test is performed.

[0112] Please see Figure 6 In some embodiments, step 011 includes:

[0113] 1109: When the difference between the fourth measured value and the third mains voltage is less than the preset value, the fourth relay is confirmed to be faulty;

[0114] 1110: When the difference between the fourth measured value and the third mains voltage is greater than or equal to the preset value, the fourth relay is confirmed to be normal.

[0115] In this way, it is possible to accurately determine whether the fourth relay 260 has failed, which is beneficial for the precise maintenance and replacement of the connection circuit 200.

[0116] In some embodiments, sub-steps 1109 and 1110 can be implemented by the control module 40, or the control module 40 can be used to confirm that the fourth relay 260 is faulty when the difference between the fourth measured value and the second grid voltage is less than a preset value; and to confirm that the fourth relay 260 is normal when the difference between the fourth measured value and the second grid voltage is greater than or equal to the preset value.

[0117] Specifically, in this embodiment, when no problem is found with the third relay 250, it is determined whether the fourth relay 260 has failed. The specific operation method is as follows:

[0118] Furthermore, the first controller 41 controls the closing of the first relay 230 and the third relay 250, while the second controller 42 controls the closing of the second relay 240 and the opening of the fourth relay 260, thereby determining the fourth measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_4 The third grid voltage V transmitted back by the third voltage acquisition module 30 Grid_3 Is the difference less than the preset value V? th That is, |V Grid_3 –V mid_4 | < V th If the condition is met, the fourth relay 260 is deemed to have failed to disconnect, and the test ends. Otherwise, the fourth relay 260 is deemed to have disconnected normally, and the next test is performed.

[0119] At this point, failure monitoring of the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260 can be completed.

[0120] In summary, the complete detection steps for determining whether a relay is malfunctioning are as follows:

[0121] First, disconnect the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260.

[0122] Furthermore, the first controller 41 and the second controller 42 simultaneously send drive signals to close the first relay 230, the second relay 240, the third relay 250, and the fourth relay 260, and determine the first inverter voltage V transmitted back from the first voltage acquisition module 10. local_1 The first grid voltage V transmitted back from the third voltage acquisition module 30 Grid_1 Is the difference less than the preset value V? th That is, |V Grid_1 -V local_1 | < V th Is the condition met? If it is met, then it is determined that the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260 can all close normally, and the next step of testing can be performed; otherwise, it is determined that the relay closure is ineffective, and the test ends.

[0123] Furthermore, the first controller 41 controls the closing of the third relay 250 and the opening of the first relay 230, while the second controller 42 controls the closing of the second relay 240 and the fourth relay 260, and determines the first measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_1The second inverter voltage V transmitted back from the first voltage acquisition module 10 local_2 Is the difference less than the preset value V? th That is, |V mid_1 -V local_2 | < V th If the condition is met, the first relay 230 is deemed to have failed to disconnect, and the test ends. Otherwise, the first relay 230 is deemed to have disconnected normally, and the next test is performed.

[0124] Furthermore, the first controller 41 controls the closing of the first relay 230 and the third relay 250, while the second controller 42 controls the closing of the fourth relay 260 and the opening of the second relay 240, and determines the second measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_2 The second grid voltage V transmitted back from the third voltage acquisition module 30 Grid_2 Is the difference less than the preset value V? th That is, |V Grid_2 –V mid_2 | < V th If the condition is met, the second relay 240 is deemed to have failed to disconnect, and the test ends. Otherwise, the second relay 240 is deemed to have disconnected normally, and the next test is performed.

[0125] Furthermore, the first controller 41 controls the closing of the first relay 230 and the opening of the third relay 250, while the second controller 42 controls the closing of the second relay 240 and the fourth relay 260, and determines the third measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_3 The third inverter voltage V transmitted back from the first voltage acquisition module 10 local_3 Is the difference less than the preset value V? th That is, |V mid_3 -V local_3 | < V th If the condition is met, the third relay 250 is deemed to have failed to disconnect, and the test ends. Otherwise, the third relay 250 is deemed to have disconnected normally, and the next test is performed.

[0126] Furthermore, the first controller 41 controls the closing of the first relay 230 and the third relay 250, while the second controller 42 controls the closing of the second relay 240 and the opening of the fourth relay 260, thereby determining the fourth measured value V of the intermediate voltage transmitted back from the second voltage acquisition module 20. mid_4 The third grid voltage V transmitted back by the third voltage acquisition module 30 Grid_3 Is the difference less than the preset value V? th That is, |V Grid_3 –V mid_4 | < V thIf the condition is met, the fourth relay 260 is deemed to have failed to disconnect, and the test ends. Otherwise, the fourth relay 260 is deemed to have disconnected normally, and the next test is performed.

[0127] Furthermore, the first controller 41 controls the closure of the first relay 230 and the third relay 250, and the second controller 42 controls the closure of the second relay 240 and the fourth relay 260. At this time, the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260 can all be closed and opened normally, and the relay self-test is completed.

[0128] Please see Figure 7 and Figure 8 In another embodiment of this application, a control circuit 100 is used to control a connection circuit 200 between the inverter 210 and the power grid 220. The connection circuit 200 includes a first relay 230, a second relay 240, a third relay 250, and a fourth relay 260. The first relay 230 and the second relay 240 are connected in series to the positive terminal of the inverter 210 and the live wire of the power grid 220. The third relay 250 and the fourth relay 260 are connected in series to the negative terminal of the inverter 210 and the neutral wire of the power grid 220. The control circuit 100 includes a first voltage acquisition module 10, a second voltage acquisition module 20, a third voltage acquisition module 30, and a control module 40. One end of the first voltage acquisition module 10 is connected to the first relay 230, and the other end is connected to the third relay 250. The first voltage acquisition module 10 is used to acquire the inverter voltage. One end of the second voltage acquisition module 20 is connected to the first relay 230 and the second relay 240, and the other end is connected to the third relay 250. One end of the second voltage acquisition module 20 is connected to the third relay 250 and the fourth relay 260. The second voltage acquisition module 20 is used to acquire the intermediate voltage. The connection point of the first relay 230 and the second relay 240 is the first connection point 270, and the connection point of the third relay 250 and the fourth relay 260 is the second connection point 280. The intermediate voltage is the voltage between the first connection point 270 and the second connection point 280. The third voltage acquisition module 30 is connected to the second relay 240 at one end and to the fourth relay 260 at the other end. The third voltage acquisition module 30 is used to acquire the grid voltage. The control module 40 is configured to control the on / off state of the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260, and to determine whether the first relay 230, the second relay 240, the third relay 250 and the fourth relay 260 are faulty based on the inverter voltage, the intermediate voltage and the grid voltage.

[0129] In this way, the control circuit 100 can accurately identify the faulty relay, which helps to reduce the difficulty and cost of maintenance.

[0130] Specifically, a voltage acquisition module is an electronic device used to acquire voltage signals. It can convert voltage signals into digital signals or other processable signal forms for subsequent data analysis, processing, or monitoring.

[0131] Please see Figure 8 In some embodiments, the control module 40 includes a first controller 41 and a second controller 42. The first controller 41 is connected to the first relay 230 and the third relay 250 and is used to control the on and off of the first relay 230 and the third relay 250. The second controller 42 is connected to the second relay 240 and the fourth relay 260 and is used to control the on and off of the second controller 42 and the second relay 240.

[0132] In this way, if either the first controller 41 or the second controller 42 fails, the other can still control the connection circuit 200 to disconnect, which helps to improve the safety of the connection circuit 200 and avoid accidents.

[0133] Specifically, in this embodiment, the first relay 230 and the third relay 250 are connected to the first controller 41, and the second relay 240 and the fourth relay 260 are connected to the first controller 41. Furthermore, the first voltage acquisition module 10, the second voltage acquisition module 20, and the third voltage acquisition module 30 are electrically connected to the first controller 41. That is, the first controller 41 is used to receive the inverter voltage acquired by the first voltage acquisition module 10, the intermediate voltage between the connection point of the first relay 230 and the second relay 240 and the connection point of the third relay 250 and the fourth relay 260 acquired by the second voltage acquisition module 20, and the grid voltage acquired by the third voltage acquisition module 30, and to determine which relay has failed based on the inverter voltage, the intermediate voltage, and the grid voltage.

[0134] In other embodiments, the first voltage acquisition module 10, the second voltage acquisition module 20, and the third voltage acquisition module 30 are electrically connected to the second controller 42. That is, the second controller 42 is used to receive the inverter voltage acquired by the first voltage acquisition module 10, the intermediate voltage between the connection point of the first relay 230 and the second relay 240 and the connection point of the third relay 250 and the fourth relay 260 acquired by the second voltage acquisition module 20, and the grid voltage acquired by the third voltage acquisition module 30, and determine which relay has failed based on the inverter voltage, the intermediate voltage, and the grid voltage.

[0135] Please see Figure 9In some embodiments, the control circuit 100 further includes a drive circuit 50. The first relay 230 includes a first coil 231. The drive circuit 50 includes a first transistor 501, a second transistor 502, a first diode 503, and a first capacitor 504. The anode of the first diode 503 is connected to a power supply, the cathode of the first diode 503 is connected to a first end of the first coil 231, the second end of the first coil 231 is connected to the collector of the second transistor 502, the emitter of the second transistor 502 is grounded, the positive terminal of the first capacitor 504 is connected to the first end of the first coil 231, the negative terminal of the first capacitor 504 is grounded, the emitter of the first transistor 501 is connected to a power supply, the collector of the first transistor 501 is connected to the negative terminal of the first capacitor 504, the base of the first transistor 501 is connected to the collector of the second transistor 502, and the base of the second transistor 502 is connected to the control module 40.

[0136] In this way, only a lower voltage is needed to activate the first relay 230, which helps reduce the power consumption and heat generation of the first relay 230, and also helps to extend the service life of the first relay 230.

[0137] Specifically, in this embodiment, the drive circuit 50 includes a first drive circuit, a second drive circuit, a third drive circuit, and a fourth drive circuit. The first controller 41 is connected to the first relay 230 through the first drive circuit, the first controller 41 is connected to the third relay 250 through the third drive circuit, the second controller 42 is connected to the second relay 240 through the second drive circuit, and the second controller 42 is connected to the fourth relay 260 through the fourth drive circuit.

[0138] Furthermore, taking the first relay 230 as an example, the principle of using the low-voltage drive circuit 50 to activate the coil of the first relay 230 is as follows:

[0139] When the first relay 230 receives a low-level control signal Control1 from the control module 40, the second transistor 502 is turned off, the first transistor 501 is turned off, the first relay 230 is in the off state, and the power supply charges the first capacitor 504 through the first diode 503 and the second resistor 507. At this time, the voltage of the first capacitor 504 is the power supply voltage VCC.

[0140] When the first relay 230 receives a high-level control signal Control1 from the control module 40, the second transistor 502 is turned on, the base of the first transistor 501 is pulled low, the first transistor 501 is turned on, the voltage of the negative terminal of the first capacitor 504 to ground is VCC, the voltage of the first capacitor 504 is VCC, so the voltage of the positive terminal of the first capacitor 504 to ground is twice VCC, the diode is reverse cut off, and the voltage twice VCC drives the first relay 230 to close.

[0141] When the first relay 230 is closed, the energy of the first capacitor 504 is released through the coil of the first relay 230, and the voltage of the first capacitor 504 decreases. When its voltage to ground is lower than the power supply VCC, the first diode 503 conducts, and the coil of the first relay 230 maintains the voltage of the power supply VCC. At this point, the drive circuit 50 completes the low-voltage drive to engage the coil of the first relay 230.

[0142] Please see Figure 9 In some embodiments, the driving circuit 50 further includes a second diode 505 and a first resistor 506. The anode of the second diode 505 is connected to the second end of the first coil 231, the cathode of the second diode 505 is connected to one end of the first resistor 506, and the other end of the first resistor 506 is connected to the first end of the first coil 231.

[0143] This is used to absorb the voltage spike generated by the first coil 231 when the first relay 230 is turned off, preventing the second transistor 502 from being damaged.

[0144] Specifically, taking the first relay 230 as an example, when the first relay 230 is turned off, the first coil 231 will generate a reverse electromotive force, causing a voltage spike to appear across the first coil 231. If this voltage spike is not properly handled, it may damage the relay or other circuit components.

[0145] In this embodiment, the second diode 505 plays a crucial role. When a voltage spike occurs, the second diode 505 quickly reverses its conduction, absorbing the spike voltage and converting it into current flowing through it, thereby protecting the circuit from damage. Preferably, the second diode 505 is a spike-absorbing diode. Furthermore, at the instant the first coil 231 is de-energized, the current in the first coil 231 does not immediately disappear but attempts to continue flowing. At this time, the second diode 505 acts as a freewheeling diode, allowing this portion of the current to flow through it, thus preventing sudden current changes from impacting the circuit.

[0146] Furthermore, the first resistor 506 serves as a current limiter in this circuit. When the second diode 505 conducts to absorb voltage spikes, the first resistor 506 limits the current flowing through the second diode 505, preventing excessive current from damaging the second diode 505 or the circuit. Simultaneously, the first resistor 506, together with the second diode 505, forms a voltage divider circuit, further reducing the amplitude of voltage spikes appearing across the first coil 231.

[0147] In this embodiment, the working principle of the second diode 505 and the first resistor 506 is as follows: When the first relay 230 is turned off, the first coil 231 generates a reverse electromotive force, causing the voltage across the first coil 231 to rise sharply. This voltage spike triggers the second diode 505 to conduct in reverse, and the second diode 505 begins to absorb the voltage spike and convert it into current. The first resistor 506 limits the current flowing through the second diode 505 to prevent excessive current from causing damage. As the second diode 505 conducts and the first resistor 506 divides the voltage, the voltage spike across the first coil 231 gradually decreases to a safe level.

[0148] In other embodiments, the second diode 505 and the first resistor 506 connected in series can be replaced by a capacitor and a resistor connected in series, which are then connected in parallel across the relay coil to form an RC snubber circuit. When the relay is turned off, the magnetic field energy stored in the coil is converted into electrical energy, generating a momentary high voltage. This high voltage is discharged through the RC circuit, where the capacitor absorbs some of the electrical energy, while the resistor limits the current. Since the charging and discharging process of the capacitor takes a certain amount of time, the RC circuit can smooth out voltage spikes, thereby protecting other components in the circuit.

[0149] In the embodiments of this application, please refer to Figure 9To improve the performance of the drive circuit 50, the drive circuit 50 also includes a second resistor 507, a third resistor 508, a fourth resistor 509, a fifth resistor 510, a sixth resistor 511, and a second capacitor 512. The connection method of each electrical component in the drive circuit 50 is as follows: the anode of the first diode 503 is connected to the power supply; the cathode of the first diode 503 is connected to the first end of the relay coil; the second end of the coil of the first relay 500 is connected to the collector of the second transistor 502; the emitter of the second transistor 502 is grounded; the anode of the second diode 505 is connected to the second end of the relay coil; the cathode of the second diode 505 is connected to one end of the first resistor 506; the other end of the first resistor 506 is connected to the first end of the relay coil; the positive terminal of the first capacitor 504 is connected to the first end of the relay coil; and the negative terminal of the first capacitor 504 is connected to the second terminal of the relay coil. One end of the second resistor 507 is connected, and the other end of the second resistor 507 is grounded. The emitter of the first transistor 501 is connected to the ground. The collector of the first transistor 501 is connected to the negative terminal of the first capacitor 504. The base of the first transistor 501 is connected to one end of the fourth resistor 509. The other end of the fourth resistor 509 is connected to the collector of the second transistor 502. The base of the second transistor 502 is connected to one end of the fifth resistor 510. The other end of the fifth resistor 510 is connected to the control signal. One end of the third resistor 508 is connected to the emitter of the first transistor 501. The other end of the third resistor 508 is connected to the base of the first transistor 501. One end of the sixth resistor 511 is connected to one end of the second capacitor 512 and to the base of the second transistor 502. The other end of the sixth resistor 511 and the other end of the second capacitor 512 are grounded.

[0150] In this embodiment, a fifth resistor 510 is connected in series with the base of the second transistor 502, and a second capacitor 512 is connected between the base and emitter of the second transistor 502 to filter out noise from the first control signal Control1. The fifth resistor 510, connected in series between the base of the second transistor 502 and the controller, provides the necessary bias voltage to the second transistor 502. This bias voltage allows the second transistor 502 to operate normally when the first controller 41 sends a signal. Furthermore, the fifth resistor 510 also limits the current flowing through the base of the second transistor 502. This not only protects the second transistor 502 from damage caused by excessive current but also prevents malfunctions caused by noise signals.

[0151] Furthermore, the fifth resistor 510 can balance the parameters in the circuit, making the circuit more stable. In the presence of fluctuating current or voltage sources, these fluctuations can be balanced by adjusting the value of the fifth resistor 510, thereby maintaining stable circuit operation.

[0152] It is important to note that the value of the fifth resistor 510 should be determined based on the magnitude of the control signal current and the characteristics of the second transistor 502. An excessively large resistor value may limit the control signal current, preventing the second transistor 502 from fully conducting or cutting off; an excessively small resistor value may result in excessive base current, increasing the power consumption and heat generation of the second transistor 502, and potentially damaging it. The fifth resistor 510 should have sufficient power to withstand the maximum current it can carry without overheating or burning out.

[0153] In this embodiment, the second capacitor 512 is connected between the base and emitter of the second transistor 502, serving as a filter. It removes high-frequency noise components from the input signal, allowing the second transistor 502 to amplify only the low-frequency portion of the signal. This results in a more accurate acquisition of the desired signal and reduces noise interference.

[0154] Furthermore, the second capacitor 512 can also improve the stability of the second transistor 502. By filtering out high-frequency noise, the second capacitor 512 makes the signal output by the second transistor 502 clearer and free of noise, thereby improving the stability of the entire circuit.

[0155] It is important to note that the capacitance of the second capacitor 512 should be determined based on the noise frequency to be filtered. A capacitance that is too small may fail to effectively filter high-frequency noise; a capacitance that is too large may introduce additional phase delay and signal distortion.

[0156] In this embodiment, the third resistor 508 is connected between the base and emitter of the first transistor 501 to provide a discharge path for the base of the first transistor 501. The sixth resistor 511 is connected between the base and emitter of the second transistor 502 to provide a discharge path for the base of the second transistor 502.

[0157] A discharge path, also known as a discharge circuit or bleed circuit, is a circuit that converts a portion of the energy stored in a circuit into heat or other forms of energy. The main principle of a discharge path is to release and collect charge through the proper connection of a resistor and a capacitor (or other energy storage element). When a capacitor (or other energy storage element) needs to be discharged, its two ends are connected to a resistor, forming a discharge circuit. In this process, the resistor provides a path for charge to flow through the capacitor (or other energy storage element), gradually reducing the amount of charge and thus releasing the energy.

[0158] In this embodiment, providing a discharge path to the base of the first transistor 501 and the base of the second transistor 502 helps protect circuit components from damage, balances energy flow in the circuit, reduces the possibility of energy accumulation and sudden changes, thereby improving circuit stability and reliability. Furthermore, the discharge path ensures timely release of charge, eliminating safety hazards and protecting the safety of personnel and equipment.

[0159] It should be noted that in the embodiments of this application, the discharge path is provided by resistors, and the resistance value should match the capacitance value of the capacitor to ensure that the capacitor can be fully discharged. If the resistance value is too large, the discharge speed will be slow; if the resistance value is too small, excessive discharge current may be generated, which may damage the circuit.

[0160] In other embodiments, a capacitor can also be used as the discharge path. It is important to note that the capacitance value should be selected based on the specific application scenario to meet the circuit requirements. Capacitors with different capacitance values ​​will exhibit different characteristics during discharge, therefore, selection must be based on the actual situation.

[0161] In the description of this specification, the references to "certain embodiments," "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples" refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0162] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the stated features. In the description of this application, "multiple" means at least two, such as two or three, unless otherwise explicitly specified.

[0163] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A control method for controlling a connection circuit between an inverter and a power grid, the connection circuit comprising a first relay, a second relay, a third relay, and a fourth relay, wherein the first relay and the second relay are connected in series to the positive terminal of the inverter and the live wire of the power grid, and the third relay and the fourth relay are connected in series to the negative terminal of the inverter and the neutral wire of the power grid, characterized in that, The control method includes: Control the closure of the first relay, the second relay, the third relay, and the fourth relay; Obtain the first inverter voltage and the first grid voltage; The first relay is disconnected, while the second, third, and fourth relays are closed. The first measured value of the intermediate voltage and the second inverter voltage are obtained. The connection point of the first relay and the second relay is the first connection point, the connection point of the third relay and the fourth relay is the second connection point, and the intermediate voltage is the voltage between the first connection point and the second connection point. The second relay is disconnected, while the first relay, the third relay, and the fourth relay are closed; Obtain a second measured value of the intermediate voltage and a second grid voltage; The third relay is disconnected, while the first, second, and fourth relays are closed. Obtain the third measured value of the intermediate voltage and the third inverter voltage; The fourth relay is disconnected, while the first, second, and third relays are closed. Obtain the fourth measured value of the intermediate voltage and the third grid voltage; Based on the first inverter voltage, the first grid voltage, the first measured value, the second inverter voltage, the second measured value, the second grid voltage, the third measured value, the third inverter voltage, the fourth measured value, and the third grid voltage, determine whether the first relay, the second relay, the third relay, and the fourth relay are faulty.

2. The control method according to claim 1, characterized in that, The determination of whether the first relay, the second relay, the third relay, and the fourth relay are faulty includes: When the difference between the first inverter voltage and the first grid voltage is less than a preset value, it is confirmed that the first relay, the second relay, the third relay and the fourth relay have not failed. When the difference between the first inverter voltage and the first grid voltage is greater than or equal to a preset value, it is confirmed that at least one of the first relay, the second relay, the third relay and the fourth relay has failed.

3. The control method according to claim 1, characterized in that, The determination of whether the first relay, the second relay, the third relay, and the fourth relay are faulty includes: When the difference between the first measured value and the second inverter voltage is less than a preset value, the first relay is confirmed to be faulty; When the difference between the first measured value and the second inverter voltage is greater than or equal to a preset value, the first relay is confirmed to be normal.

4. The control method according to claim 1, characterized in that, The determination of whether the first relay, the second relay, the third relay, and the fourth relay are faulty includes: When the difference between the second measured value and the second mains voltage is less than a preset value, the second relay is confirmed to be faulty; When the difference between the second measured value and the second mains voltage is greater than or equal to a preset value, the second relay is confirmed to be normal.

5. The control method according to claim 1, characterized in that, The determination of whether the first relay, the second relay, the third relay, and the fourth relay are faulty includes: When the difference between the third measured value and the third inverter voltage is less than a preset value, the third relay is confirmed to be faulty. When the difference between the third measured value and the third inverter voltage is greater than or equal to a preset value, the third relay is confirmed to be normal.

6. The control method according to claim 1, characterized in that, The determination of whether the first relay, the second relay, the third relay, and the fourth relay are faulty includes: When the difference between the fourth measured value and the third mains voltage is less than a preset value, the fourth relay is confirmed to be faulty; When the difference between the fourth measured value and the third mains voltage is greater than or equal to a preset value, the fourth relay is confirmed to be normal.

7. A control circuit for controlling the connection circuit between an inverter and the power grid, the connection circuit comprising a first relay, a second relay, a third relay, and a fourth relay, wherein the first relay and the second relay are connected in series to the positive terminal of the inverter and the live wire of the power grid, and the third relay and the fourth relay are connected in series to the negative terminal of the inverter and the neutral wire of the power grid, characterized in that... The control circuit includes: A first voltage acquisition module is connected at one end to the first relay and at the other end to the third relay. The first voltage acquisition module is used to acquire inverter voltage. The second voltage acquisition module has one end connected to the first relay and the second relay, and the other end connected to the third relay and the fourth relay. The second voltage acquisition module is used to acquire intermediate voltage. The connection point between the first relay and the second relay is the first connection point, and the connection point between the third relay and the fourth relay is the second connection point. The intermediate voltage is the voltage between the first connection point and the second connection point. The third voltage acquisition module is connected at one end to the second relay and at the other end to the fourth relay. The third voltage acquisition module is used to acquire the grid voltage. The control module is configured to control the on / off state of the first relay, the second relay, the third relay, and the fourth relay, and to determine whether the first relay, the second relay, the third relay, and the fourth relay are faulty based on the inverter voltage, the intermediate voltage, and the grid voltage.

8. The control circuit according to claim 7, characterized in that, The control module includes a first controller and a second controller. The first controller is connected to the first relay and the third relay respectively and is used to control the on / off state of the first relay and the third relay. The second controller is connected to the second relay and the fourth relay respectively and is used to control the on / off state of the second controller and the second relay.

9. The control circuit according to claim 7, characterized in that, The control circuit further includes a drive circuit. The first relay includes a first coil. The drive circuit includes a first transistor, a second transistor, a first diode, and a first capacitor. The first diode is connected to a power supply. The cathode of the first diode is connected to a first end of the first coil. The second end of the first coil is connected to the collector of the second transistor. The emitter of the second transistor is grounded. The anode of the first capacitor is connected to the first end of the first coil. The cathode of the first capacitor is grounded. The emitter of the first transistor is connected to the power supply. The collector of the first transistor is connected to the cathode of the first capacitor. The base of the first transistor is connected to the collector of the second transistor. The base of the second transistor is connected to the control module.

10. The control circuit according to claim 9, characterized in that, The driving circuit further includes a second diode and a first resistor. The anode of the second diode is connected to the second end of the first coil, the cathode of the second diode is connected to one end of the first resistor, and the other end of the first resistor is connected to the first end of the first coil.

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