Fault detection method of zero line relay and power conversion system

Abstract

The invention discloses a fault detection method for null line relays, which is applied to a power conversion system, the power conversion system comprises a power converter and n null line relays, the power converter is connected to a power grid null line through the n null line relays, and n is a positive integer greater than or equal to 2; the fault detection method comprises the following steps: controlling n-1 zero line relays to be closed and disconnecting a target zero line relay; driving the power converter, and detecting an inductive current of a target inductor and a capacitor voltage of a bus capacitor in the power converter; when it is determined that the inductive current is in a preset direction and is larger than a preset current value, and it is determined that the capacitor voltage is larger than a preset voltage value, it is determined that the target zero line relay has an adhesion fault; and returning to the step of controlling the n-1 null line relays to be closed and the target null line relay to be opened until all the null line relays are detected. Whether the zero line relay has an adhesion fault can be correctly detected.

Description

Technical Field

[0001] The present application relates to the technical field of relay detection, and in particular to a fault detection method for a neutral line relay and a power conversion system. Background Art

[0002] At present, power conversion systems are widely used. Through the power conversion system, the DC voltage generated by photovoltaic modules can be converted into AC voltage to power the load and sell electricity to the power grid. The power converter in the power conversion system is connected to the power grid through a relay.

[0003] Since the relay needs to transmit a large current, the metal contacts are prone to adhesion after long-term use, which can cause the relay to fail to disconnect in time when needed, which may have a series of impacts on the normal operation of the power conversion system. Therefore, the relay adhesion fault detection is required before the power conversion system works. However, when the neutral terminal of the power inverter is close to the ground potential of the power grid, the existing relay adhesion detection method cannot correctly detect whether the neutral relay has a adhesion fault. Summary of the invention

[0004] In view of this, the present application provides a fault detection method for a neutral line relay and a power conversion system, which are used to correctly detect whether a neutral line relay has a sticking fault. The technical solution of the present application is as follows: A first aspect of the present application provides a fault detection method for a neutral line relay, which is applied to a power conversion system, wherein the power conversion system includes a power converter and n neutral line relays, wherein the power converter is connected to the neutral line of a power grid via the n neutral line relays, where n is a positive integer greater than or equal to 2; the fault detection method includes: controlling n-1 neutral line relays to close and disconnect a target neutral line relay; driving the power converter, and detecting the inductive current of a target inductor and the capacitive voltage of a bus capacitor in the power converter; determining that the target neutral line relay has a sticking fault when the inductive current is in a preset direction and is greater than a preset current value, and when the capacitive voltage is greater than a preset voltage value; and returning to the step of controlling n-1 neutral line relays to close and disconnect the target neutral line relay until all the neutral line relays are detected.

[0005] In one embodiment of the present application, the power conversion system also includes m live wire relays, and the power converter is connected to the live wire of the power grid through the m live wire relays, where m is a positive integer greater than or equal to 2; before controlling the n-1 neutral wire relays to close and disconnecting the target neutral wire relay, it also includes: controlling all the live wire relays to close.

[0006] In one embodiment of the present application, the power conversion system also includes m live wire relays, and the power converter is connected to the live wire of the power grid through the m live wire relays, where m is a positive integer greater than or equal to 2; before controlling the n-1 neutral line relays to close and disconnect the target neutral line relay, it also includes: detecting all the live wire relays, and after determining that all the live wire relays are working normally, controlling all the live wire relays to close; and executing the step of controlling the n-1 neutral line relays to close and disconnecting the target neutral line relay.

[0007] In one embodiment of the present application, the power conversion system also includes m live wire relays, and the power converter is connected to the live wire of the power grid through the m live wire relays, where m is a positive integer greater than or equal to 2; the fault detection method also includes: after determining that all the neutral wire relays are working normally, controlling the neutral wire relay to close, detecting all the live wire relays, and determining whether there is a live wire relay with a sticking fault.

[0008] In one embodiment of the present application, the detection of all the live wire relays includes: controlling all the neutral wire relays to close; controlling m-1 of the live wire relays to close and disconnecting the target live wire relay; obtaining a first voltage of the live wire port of the power converter, and obtaining a second voltage of the live wire of the power grid; determining that the target live wire relay has a sticking fault when a voltage difference between the first voltage and the second voltage is greater than a preset threshold; and returning to the step of controlling m-1 of the live wire relays to close and disconnecting the target live wire relay until all the live wire relays are detected.

[0009] A second aspect of the present application provides a power conversion system, including a power converter, n neutral line relays and a controller, wherein the power converter is connected to the neutral line of a power grid through the n neutral line relays, where n is a positive integer greater than or equal to 2; the controller is connected to the power converter and the neutral line relay, and is used to: control n-1 neutral line relays to close and disconnect the target neutral line relay, drive the power converter, and detect the inductive current of the target inductor and the capacitor voltage of the bus capacitor in the power converter, determine that the inductive current is in a preset direction and is greater than a preset current value, and determine that the capacitor voltage is greater than a preset voltage value, determine that the target neutral line relay has a adhesion fault, and return to the step of controlling the n-1 neutral line relays to close and disconnect the target neutral line relay until all the neutral line relays are detected.

[0010] In one embodiment of the present application, the power conversion system also includes m live line relays, and the power converter is connected to the live line of the power grid through the m live line relays, where m is a positive integer greater than or equal to 2; the controller is connected to the live line relays, and the controller is also used to control all the live line relays to close before controlling n-1 neutral line relays to close and disconnecting the target neutral line relay.

[0011] In one embodiment of the present application, the power conversion system also includes m live wire relays, and the power converter is connected to the live wire of the power grid through the m live wire relays, where m is a positive integer greater than or equal to 2; the controller is connected to the live wire relays, and the controller is also used to detect all the live wire relays before controlling n-1 neutral line relays to close and disconnect the target neutral line relay, and after determining that all the live wire relays are working normally, control all the live wire relays to close, and execute the steps of controlling the n-1 neutral line relays to close and disconnect the target neutral line relay.

[0012] In one embodiment of the present application, the power conversion system also includes m live wire relays, and the power converter is connected to the live wire of the power grid through the m live wire relays, where m is a positive integer greater than or equal to 2; the controller is connected to the live wire relays, and the controller is also used to control the neutral wire relay to close after determining that all the neutral wire relays are working normally, and to detect all the live wire relays to determine whether there is a live wire relay with a sticking fault.

[0013] In one embodiment of the present application, when the controller detects all the live wire relays, it is used to control all the neutral wire relays to close, control m-1 of the live wire relays to close and disconnect the target live wire relay, obtain the first voltage of the live wire port of the power converter, and obtain the second voltage of the live wire of the power grid. When it is determined that the voltage difference between the first voltage and the second voltage is greater than a preset threshold, it is determined that the target live wire relay has a sticking fault, and the process returns to the step of controlling the m-1 live wire relays to close and disconnect the target live wire relay until all the live wire relays are detected.

[0014] When detecting whether the target neutral line relay has a sticking fault, the present application drives the power converter and detects the inductive current of the target inductor and the capacitive voltage of the bus capacitor, and determines whether the target neutral line relay has a sticking fault based on the direction and magnitude of the inductive current and the magnitude of the capacitive voltage. Even when the neutral line terminal of the power inverter is close to the ground potential of the power grid, it is possible to accurately detect whether the target neutral line relay has a sticking fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic block diagram of a power conversion system provided in an embodiment of the present application.

[0016] Figure 2 It is a flow chart of a fault detection method for a neutral line relay provided in an embodiment of the present application.

[0017] Figure 3 It is a schematic block diagram of another power conversion system provided in an embodiment of the present application.

[0018] Figure 4 It is a flow chart of another method for detecting a fault of a neutral line relay provided in an embodiment of the present application.

[0019] Figure 5 It is a flow chart of the third method for detecting faults of a neutral line relay provided in an embodiment of the present application.

[0020] Figure 6 It is a flow chart of the fourth method for detecting faults of a neutral line relay provided in an embodiment of the present application.

[0021] Figure 7 It is a flow chart of a method for detecting a live wire relay provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] It should be noted that in the embodiments of the present application, "at least one" refers to one or more, and "more than one" refers to two or more than two. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The terms "first", "second", "third", "fourth", etc. (if any) in the specification, claims and drawings of this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0023] It should also be noted that the method disclosed in the embodiments of the present application or the method shown in the flowchart includes one or more steps for implementing the method. Without departing from the scope of the claims, the execution order of multiple steps can be interchanged with each other, and some of the steps can also be deleted.

[0024] At present, power conversion systems are widely used. Through the power conversion system, the DC voltage generated by photovoltaic modules can be converted into AC voltage to power the load and sell electricity to the power grid. The power converter in the power conversion system is connected to the power grid through a relay.

[0025] Since the relay needs to transmit a large current, the metal contacts are prone to adhesion after long-term use, which can cause the relay to fail to disconnect in time when needed, which may have a series of impacts on the normal operation of the power conversion system. Therefore, the relay adhesion fault detection is required before the power conversion system works. However, when the neutral terminal of the power inverter is close to the ground potential of the power grid, the existing relay adhesion detection method cannot correctly detect whether the neutral relay has a adhesion fault.

[0026] The present application provides a fault detection method for a neutral line relay and a power conversion system, which are used to correctly detect whether a neutral line relay has a sticking fault.

[0027] Please refer to Figure 1 , Figure 1 A schematic block diagram of a power conversion system provided in an embodiment of the present application, wherein the power conversion system 100 includes a power converter 110 and n neutral line relays 120 .

[0028] In the embodiment of the present application, the power converter 110 is connected to the neutral line of the power grid 101 through n neutral line relays 120 , where n is a positive integer greater than or equal to 2 (n is 2 in the example in the figure).

[0029] Next, combine Figure 1 A method for detecting a fault of a neutral relay provided in an embodiment of the present invention is described in detail. Figure 2 , specifically including the following steps: Step S21: Control n-1 neutral line relays to close and open the target neutral line relay.

[0030] In the embodiment of the present application, a controller may also be provided in the power conversion system, which is connected to the power converter and each neutral line relay, and the controller is used to transmit a drive signal to the power converter, so that the power converter enters a working state, converts a DC voltage into an AC voltage and transmits it to the power grid, or receives an AC voltage from the power grid, converts the AC voltage into a DC voltage and transmits it to the load. The controller is also used to transmit a control signal to the neutral line relay to control all the neutral line relays to close, so that the neutral line end of the power converter is connected to the neutral line of the power grid, or to control all the neutral line relays to disconnect, so that the neutral line end of the power converter is disconnected from the neutral line of the power grid.

[0031] In some embodiments, when the power conversion system is started and before the power converter enters the working state, the controller can first execute the fault detection method in the present scheme to perform fault detection of the neutral line relay before the power converter works normally, so as to avoid abnormalities in the grid-connected process and the grid-off process of the power conversion system.

[0032] When entering the fault detection state of the neutral line relay, the controller first selects one of the neutral line relays as the target neutral line relay, controls n-1 neutral line relays to close and disconnects the target neutral line relay. In some embodiments, the controller can select one of the neutral line relays as the target neutral line relay in a preset order, which is not limited here.

[0033] Step S22: driving the power converter and detecting the inductor current of the target inductor and the capacitor voltage of the bus capacitor in the power converter.

[0034] In the embodiment of the present application, after the controller confirms that n-1 neutral relays are closed and the target neutral relay is disconnected, the controller transmits a drive signal to the power converter to drive the power converter to work. After the power converter works, the controller further detects the inductor current of the target inductor in the power converter and the capacitor voltage of the bus capacitor.

[0035] In some embodiments, a current sampling circuit and a voltage sampling circuit may be provided in the power converter. The current sampling circuit is used to collect the inductor current of the target inductor and transmit it to the controller. The voltage sampling circuit is used to collect the capacitor voltage of the bus capacitor and transmit it to the controller.

[0036] Step S23: When it is determined that the inductor current is in a preset direction and is greater than a preset current value, and when it is determined that the capacitor voltage is greater than a preset voltage value, a target neutral line relay adhesion fault is determined.

[0037] In an embodiment of the present application, after obtaining the inductor current and the capacitor voltage, the controller detects the direction of the inductor current, compares the inductor current with a preset current value, and compares the capacitor voltage with a preset voltage value. When it is determined that the inductor current is in the preset direction and is greater than the preset current value, and at the same time determines that the capacitor voltage is greater than the preset voltage value, the controller determines that the target neutral line relay has a sticking fault.

[0038] In some embodiments, when the controller determines that there is a target neutral relay sticking fault, the controller may stop driving the power converter and stop the power conversion system from operating.

[0039] Step S24: Return to step S21 until all neutral line relays are detected.

[0040] In an embodiment of the present application, after the controller detects the target neutral line relay, it can select the next neutral line relay as the target relay until all the neutral line relays are detected. It can be understood that when the present application detects whether the target neutral line relay has a sticking fault, it drives the power converter and detects the inductor current of the target inductor and the capacitor voltage of the bus capacitor, and determines whether the target neutral line relay has a sticking fault according to the direction and magnitude of the inductor current and the magnitude of the capacitor voltage. Even when the neutral line terminal of the power inverter is close to the ground potential of the power grid, it can accurately detect whether the target neutral line relay has a sticking fault.

[0041] Please refer to Figure 3 , Figure 3 A schematic block diagram of another power conversion system provided in an embodiment of the present application, wherein: Figure 3 The power conversion system 100 shown is Figure 2 Compared with the power conversion system 100 shown in the figure, the difference is that it further includes m live wire relays 130 (in the example in the figure, m is 2).

[0042] In the embodiment of the present application, the power converter 110 is connected to the live line of the power grid 101 through m live line relays 130 , where m is a positive integer greater than or equal to 2.

[0043] In some embodiments, Figure 4 The fault detection method shown comprises: Step S41: Control all live wire relays to close.

[0044] Step S42: Control n-1 neutral line relays to close and open the target neutral line relay.

[0045] Step S43: driving the power converter and detecting the inductor current of the target inductor and the capacitor voltage of the bus capacitor in the power converter.

[0046] Step S44: When it is determined that the inductor current is in a preset direction and is greater than a preset current value, and when it is determined that the capacitor voltage is greater than a preset voltage value, a target neutral line relay adhesion fault is determined.

[0047] Step S45: Return to step S42 until all neutral line relays are detected.

[0048] In the embodiment of the present application, before performing the adhesion fault detection of the neutral line relay, the controller may also control all the live line relays to close, so as to form a loop between the power converter and the power grid.

[0049] In some embodiments, Figure 5 The fault detection method shown comprises: Step S51: Detect all live relays, and after confirming that all live relays are working normally, control all live relays to close.

[0050] In the embodiment of the present application, before performing adhesion fault detection on the neutral relay, the controller may first detect all live relays, and after confirming that all live relays are working normally, perform adhesion fault detection on the neutral relay. In some embodiments, the detection of the live relay includes adhesion fault detection.

[0051] Step S52: Control n-1 neutral line relays to close and open the target neutral line relay.

[0052] Step S53: driving the power converter and detecting the inductor current of the target inductor and the capacitor voltage of the bus capacitor in the power converter.

[0053] Step S54: When it is determined that the inductor current is in a preset direction and is greater than a preset current value, and when it is determined that the capacitor voltage is greater than a preset voltage value, a target neutral line relay adhesion fault is determined.

[0054] Step S55: Return to step S52 until all neutral line relays are detected.

[0055] In some embodiments, Figure 6 The fault detection method shown is similar to Figure 2 Compared with the fault detection method shown in the figure, the difference is that it also includes: Step S65: After determining that all neutral relays are working normally, control the neutral relay to close, and detect all live relays to determine whether there is a live relay with a sticking fault.

[0056] In the embodiment of the present application, the controller may also first perform a fault detection on all neutral line relays, and after determining that the neutral line relay is operating normally, perform a sticking detection on all live line relays.

[0057] Please refer to Figure 7 , Figure 7 A flow chart of a method for detecting a live wire relay provided in an embodiment of the present application specifically includes the following steps: Step S71: Control all neutral line relays to close.

[0058] Step S72: Control m-1 live relays to close and open the target live relay.

[0059] Step S73: obtaining a first voltage of the live wire port of the power converter, and obtaining a second voltage of the live wire of the power grid.

[0060] Step S74: When it is determined that the voltage difference between the first voltage and the second voltage is greater than a preset threshold, it is determined that the target live wire relay has a sticking fault.

[0061] Step S75: Return to step S72 until all live wire relays are detected.

[0062] An embodiment of the present application also provides a power conversion system, wherein the power conversion system includes a power converter, n neutral line relays and a controller, the power converter is connected to the neutral line of the power grid through the n neutral line relays, and n is a positive integer greater than or equal to 2.

[0063] Among them, the controller is connected to the power converter and the neutral line relay, and the controller is used to: control n-1 neutral line relays to close and disconnect the target neutral line relay, drive the power converter, and detect the inductor current of the target inductor and the capacitor voltage of the bus capacitor in the power converter, determine that the inductor current is in a preset direction and is greater than a preset current value, and determine that the capacitor voltage is greater than a preset voltage value, determine that the target neutral line relay has a sticking fault, and return to the step of controlling the n-1 neutral line relays to close and disconnect the target neutral line relay until all neutral line relays are detected.

[0064] In some embodiments, the power conversion system further includes m live line relays, and the power converter is connected to the live line of the power grid through the m live line relays, where m is a positive integer greater than or equal to 2. The controller is connected to the live line relays, and the controller is further configured to control all the live line relays to close before controlling n-1 neutral line relays to close and disconnecting the target neutral line relay.

[0065] In some embodiments, the power conversion system further includes m live line relays, and the power converter is connected to the live line of the power grid through the m live line relays, where m is a positive integer greater than or equal to 2. The controller is connected to the live line relays, and the controller is also used to detect all live line relays before controlling n-1 neutral line relays to close and disconnect the target neutral line relay, and after determining that all live line relays are working normally, control all live line relays to close, and execute the steps of controlling n-1 neutral line relays to close and disconnect the target neutral line relay.

[0066] In some embodiments, the power conversion system further includes m live line relays, and the power converter is connected to the live line of the power grid through the m live line relays, where m is a positive integer greater than or equal to 2. The controller is connected to the live line relays, and the controller is also used to control the neutral line relay to close after determining that all neutral line relays are working normally, and to detect all live line relays to determine whether there is a live line relay with a sticking fault.

[0067] In some embodiments, when the controller detects all live wire relays, it is used to control all neutral wire relays to close, control m-1 live wire relays to close and disconnect the target live wire relay, obtain a first voltage at the live wire port of the power converter, and obtain a second voltage at the live wire of the power grid. When it is determined that the voltage difference between the first voltage and the second voltage is greater than a preset threshold, it is determined that the target live wire relay has a sticking fault, and the controller returns to the step of controlling m-1 live wire relays to close and disconnect the target live wire relay until all live wire relays are detected.

[0068] An embodiment of the present application further provides a computer storage medium, which stores a computer program. When the computer program is executed by a processor, the processor executes the above-mentioned fault detection method.

[0069] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer storage medium or transmitted through the computer storage medium. The computer instructions may be transmitted from a website site, computer, server or data center to another website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a digital versatile disc (DVD)), or a semiconductor medium (eg, a solid state disk (SSD)).

[0070] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk and other media that can store program codes. In the absence of conflict, the technical features in this embodiment and the implementation scheme can be combined arbitrarily.

[0071] The embodiments described above are merely preferred embodiments of the present application and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements made to the technical solutions of the present application by ordinary technicians in this field should fall within the protection scope determined by the claims of the present application.

Claims

1. A method for detecting a fault of a neutral line relay, characterized in that: Applied to a power conversion system, the power conversion system comprises a power converter and n neutral line relays, the power converter is connected to a neutral line of a power grid through the n neutral line relays, and n is a positive integer greater than or equal to 2; The fault detection method comprises: Controlling n-1 of the neutral line relays to close and disconnecting the target neutral line relay; driving the power converter, and detecting an inductor current of a target inductor and a capacitor voltage of a bus capacitor in the power converter; When it is determined that the inductor current is in a preset direction and is greater than a preset current value, and when it is determined that the capacitor voltage is greater than a preset voltage value, it is determined that the target neutral line relay has a sticking fault; Return to the step of controlling n-1 of the neutral line relays to close and disconnect the target neutral line relay until all the neutral line relays are detected.

2. The fault detection method according to claim 1, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; Before controlling the n-1 neutral line relays to close and disconnect the target neutral line relay, the method further includes: Control all the live wire relays to close.

3. The fault detection method according to claim 1, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; Before controlling the n-1 neutral line relays to close and disconnect the target neutral line relay, the method further includes: Detecting all the live wire relays, and after confirming that all the live wire relays are working normally, controlling all the live wire relays to close; The step of controlling the n-1 neutral line relays to close and the target neutral line relay to open is performed.

4. The fault detection method according to claim 1, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; The fault detection method further comprises: After determining that all the neutral line relays are working normally, the neutral line relay is controlled to close, and all the live line relays are detected to determine whether there is a live line relay with a sticking fault.

5. The fault detection method according to claim 3 or 4, characterized in that: The detecting all the live relays comprises: Controlling all the neutral line relays to close; Control m-1 of the live wire relays to close and disconnect the target live wire relay; Acquire a first voltage of a live wire port of the power converter, and acquire a second voltage of a live wire of the power grid; When it is determined that the voltage difference between the first voltage and the second voltage is greater than a preset threshold, determining that the target live wire relay has a sticking fault; Return to the step of controlling the m-1 live wire relays to close and the target live wire relay to open, until all the live wire relays are detected.

6. A power conversion system, characterized in that: It comprises a power converter, n zero line relays and a controller, wherein the power converter is connected to the zero line of a power grid through the n zero line relays, and n is a positive integer greater than or equal to 2; The controller is connected to the power converter and the neutral line relay, and is used to: control n-1 of the neutral line relays to close and disconnect the target neutral line relay, drive the power converter, and detect the inductive current of the target inductor and the capacitor voltage of the bus capacitor in the power converter, and when it is determined that the inductive current is in a preset direction and is greater than a preset current value, and when it is determined that the capacitor voltage is greater than a preset voltage value, it is determined that the target neutral line relay has a sticking fault, and return to the step of controlling the n-1 neutral line relays to close and disconnect the target neutral line relay until all the neutral line relays are detected.

7. The power conversion system according to claim 6, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; The controller is connected to the live line relays, and is further configured to control all the live line relays to be closed before controlling n-1 neutral line relays to be closed and disconnecting a target neutral line relay.

8. The power conversion system according to claim 6, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; The controller is connected to the live wire relay, and is also used to detect all the live wire relays before controlling n-1 neutral wire relays to close and disconnect the target neutral wire relay, and after determining that all the live wire relays are working normally, control all the live wire relays to close, and execute the steps of controlling n-1 neutral wire relays to close and disconnect the target neutral wire relay.

9. The power conversion system according to claim 6, characterized in that: The power conversion system further includes m live wire relays, the power converter is connected to the live wire of the power grid through the m live wire relays, and m is a positive integer greater than or equal to 2; The controller is connected to the live wire relay, and is further used to control the neutral wire relay to close after determining that all the neutral wire relays are working normally, and to detect all the live wire relays to determine whether there is a live wire relay with a sticking fault.

10. The power conversion system according to claim 8 or 9, characterized in that: When the controller detects all the live wire relays, it is used to control all the neutral wire relays to close, control m-1 of the live wire relays to close and disconnect the target live wire relay, obtain the first voltage of the live wire port of the power converter, and obtain the second voltage of the live wire of the power grid. When it is determined that the voltage difference between the first voltage and the second voltage is greater than a preset threshold, it is determined that the target live wire relay has a sticking fault, and the controller returns to the step of controlling the m-1 live wire relays to close and disconnect the target live wire relay until all the live wire relays are detected.

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