A current source type grid-connected inverter internal relay fault detection method

Abstract

The present application relates to a kind of current source type grid-connected inverter internal relay fault detection method, utilize the inherent current source characteristics of inverter itself and existing hardware protection circuit, complete fault diagnosis can be realized by software algorithm logic.This greatly simplifies hardware design, saves cost, eliminates additional loss, improves system efficiency, since completely avoids the introduction of sampling resistance and other energy-consuming elements in power loop or detection loop, the present application completely eliminates the additional power loss caused by traditional detection method, which enables grid-connected inverter to maintain its highest power generation efficiency, the method does not introduce new, possibly itself failure fault point, avoids false alarm or miss report caused by detection circuit itself failure, makes the fault detection function itself more reliable, thereby improves the running stability and safety of whole machine, through ingenious software process design, forms a complete, closed loop, adaptive intelligent diagnosis process.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and specifically to a method for detecting internal relay faults in a current source type grid-connected inverter. Background Technology

[0002] Grid-connected inverters are critical devices connecting distributed generation units (such as photovoltaic modules and batteries) to the public power grid, and their reliability and safety are paramount. Inverters typically contain a grid-connection relay to control the connection and disconnection between the inverter and the grid. This relay closes during system startup, supplying power to the grid; it disconnects during system shutdown, faults, or when maintenance is required, ensuring the safety of equipment and personnel. As a mechanical switching element, relays are susceptible to two typical faults after prolonged use: open-circuit faults, preventing normal closing and thus preventing grid connection; and sticking faults, preventing normal disconnection and preventing the inverter from disconnecting from the grid when needed, posing a significant safety hazard, such as feeding power back into the grid during a power outage, endangering the lives of maintenance personnel.

[0003] Therefore, checking the relay status through a power-on self-test program before the inverter is connected to the grid is a necessary step to ensure the safe and reliable operation of the system. Currently, the most common method for relay fault detection is to add an extra dedicated detection circuit. However, these traditional solutions suffer from high system complexity, high cost, and the introduction of additional power consumption, which reduces the overall power generation efficiency of the unit. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for detecting internal relay faults in a current source grid-connected inverter.

[0005] To achieve the above objectives, this application provides a method for detecting internal relay faults in a current-source grid-connected inverter, comprising:

[0006] The control unit sends a first preset check command to the inverter;

[0007] The inverter receives and executes the first preset check command;

[0008] A first feedback signal is generated based on the inverter's execution result and sent to the control unit.

[0009] The control unit receives a first feedback signal and generates a first detection result based on the first feedback signal;

[0010] Alternatively, the control unit receives the first feedback signal, generates a second preset check command based on the first feedback signal, and sends it to the inverter;

[0011] The inverter accepts and executes the second preset check command;

[0012] The second feedback signal generated based on the inverter's execution process is acquired and sent to the control unit;

[0013] The control unit receives a second feedback signal and generates a second detection result based on the second feedback signal.

[0014] The final test result is generated and output based on either the first or second test result.

[0015] In some embodiments, the first preset check command is configured to control the relay to remain in the open state, and to control the inverter to perform grid connection operation according to the first preset power for a first preset time;

[0016] The first feedback signal is configured as the status information of the overvoltage protection circuit, which includes either the circuit on state or the circuit off state.

[0017] In some embodiments, the method further includes:

[0018] The state information is determined according to the first preset discrimination condition to obtain the first discrimination result. The first preset discrimination condition is configured to determine whether the overvoltage protection circuit is triggered.

[0019] A second preset check instruction is generated based on the first discrimination result;

[0020] Alternatively, generate and output the first detection result based on the first discrimination result.

[0021] In some embodiments, if the status information is that the circuit is on, it indicates that the overvoltage protection circuit has been triggered, the first judgment result is normal, and a second preset check instruction is generated based on the first judgment result.

[0022] If the status information indicates that the circuit is off, it means that the overvoltage protection circuit has not been triggered. The first judgment result is an adhesion abnormality, and the first detection result is generated based on the first judgment result.

[0023] In some embodiments, if the status information is a circuit closed state, it indicates that the overvoltage protection circuit has not been triggered, the first determination result is an adhesion abnormality, and a third preset check instruction is generated based on the first determination result. The third preset check instruction is configured to control the relay to remain closed, then control the relay to remain open again, and control the inverter to perform grid connection operation according to the third preset power for a third preset time.

[0024] The method also includes:

[0025] Acquire a third feedback signal, which is configured as the status information of the overvoltage protection circuit after executing a third preset check command;

[0026] The status information of the overvoltage protection circuit after executing the third preset check command is determined based on the first preset discrimination condition, and the third discrimination result is obtained.

[0027] The third discrimination result is integrated with the first discrimination result to generate the first detection result and output it.

[0028] In some embodiments, the first preset power is 0.5% to 2.0% of the rated value within the inverter's safety margin range;

[0029] The first preset time is 1 to 5 inverter switching cycles.

[0030] In some embodiments, the second preset check command is configured to control the relay to remain closed, and to control the inverter to perform grid connection operation at a second preset power for a second preset time.

[0031] The second feedback signal is configured to be the actual grid-connected power information.

[0032] In some embodiments, the control unit receives a second feedback signal and generates a second detection result based on the second feedback signal, including:

[0033] Calculate the power deviation between the actual grid-connected power and the second preset power;

[0034] The power deviation value is determined according to the second preset discrimination condition, and a second discrimination result is obtained. The second preset discrimination condition is configured to determine whether the power deviation value exceeds the preset deviation threshold range.

[0035] A second detection result is generated based on the second discrimination result.

[0036] In some embodiments, if the power deviation value is within the range of a preset deviation threshold, the second discrimination result is normal;

[0037] If the power deviation value exceeds the preset deviation threshold range of the rated value;

[0038] The second preset time is 1 to 5 inverter switching cycles.

[0039] Unlike existing technologies, the above technical solution involves the control unit sending a first preset check command to the inverter and receiving a first feedback signal generated after its execution, thereby generating a first detection result or a second preset check command. In subsequent processes, a second feedback signal is obtained based on the execution result of the second preset check command, and a second detection result is generated, ultimately outputting a comprehensive detection result. This method fully utilizes the inherent characteristics of the current-source grid-connected inverter and existing hardware overvoltage protection circuits, implementing relay open-circuit and sticking fault detection through software logic without the need for any additional external detection circuits. This design significantly reduces system complexity and cost, completely eliminates the additional power consumption caused by traditional sampling resistors, helps maintain the inverter's high-efficiency power generation performance, and avoids false alarms or missed alarms caused by faults in the additional detection circuits themselves, greatly improving the reliability of fault diagnosis functions and the overall operational safety of the unit.

[0040] The above description of the invention is merely an overview of the technical solution of this application. In order to enable those skilled in the art to better understand the technical solution of this application and to implement it based on the description and drawings, and to make the above-mentioned objectives and other objectives, features and advantages of this application easier to understand, the following description is provided in conjunction with the specific embodiments and drawings of this application. Attached Figure Description

[0041] The accompanying drawings are only used to illustrate the principles, implementation methods, applications, features, and effects of specific embodiments of the present invention and other related contents, and should not be considered as limitations on this application.

[0042] In the accompanying drawings of the instruction manual:

[0043] Figure 1 This is a schematic diagram illustrating steps S101 to S104 as described in the specific implementation method;

[0044] Figure 2 This is a schematic diagram illustrating steps S201 to S202 as described in the specific implementation method;

[0045] Figure 3 This is a schematic diagram illustrating the steps described in the specific implementation method. Detailed Implementation

[0046] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0047] Please see Figure 1This embodiment provides a method for detecting internal relay faults in a current-source grid-connected inverter, including:

[0048] S101, The control unit sends a first preset check command to the inverter, and the inverter receives and executes the first preset check command.

[0049] S102. Generate a first feedback signal based on the execution result of the inverter, and send the first feedback signal to the control unit. The control unit receives the first feedback signal and generates a first detection result based on the first feedback signal. Alternatively, the control unit receives the first feedback signal, generates a second preset check instruction based on the first feedback signal, and sends it to the inverter. The inverter accepts the second preset check instruction and executes it.

[0050] S103. Obtain the second feedback signal generated according to the execution process of the inverter and send it to the control unit. The control unit receives the second feedback signal and generates a second detection result based on the second feedback signal.

[0051] S104. Generate and output the final detection result based on the first or second detection result.

[0052] In step S101, the control unit sends the first preset check instruction, which means that the detection logic is implemented by executing a pre-stored software program or firmware. The first preset check instruction includes the setting of inverter circuit status, grid-connected power, and switching cycle. The circuit status includes two states: open and closed. The first preset check instruction is performed by sending the instruction from the control unit, which eliminates the need to add an additional resistor sampling circuit, thereby eliminating additional losses and improving system efficiency.

[0053] In step S102, generating the first feedback signal based on the inverter's execution result means generating the first feedback signal and sending it to the control unit based on the status information of whether the inverter's overvoltage protection circuit has been triggered. Based on the principle that the voltage at the open-circuit point of a current-source grid-connected inverter continuously increases according to the open-circuit impedance, after the inverter performs circuit disconnection and inputs grid-connected voltage according to the set switching cycle, if the overvoltage protection circuit is triggered, the controller outputs the first detection result indicating that the inverter's internal relay status self-test has passed. If the overvoltage protection circuit is not triggered, a relay sticking fault is suspected, i.e., the relay cannot disconnect. The controller generates a second preset check command and sends it to the inverter. This command first controls the relay to close and then controls the inverter to attempt grid connection at a second preset power. The second preset power is determined based on the inverter's capacity. Within a safety margin, after a second preset time, the relay is controlled to disconnect, and the grid-connected power at this time is detected. This detection method utilizes the common characteristics of current-source inverters and has wide applicability and versatility.

[0054] In step S103, the second feedback signal is the actual grid-connected power. If the actual grid-connected power is greater than 0, it is determined that the relay is in a sticking fault state. If the actual grid-connected power is equal to 0, it is determined that the relay sticking fault has been resolved and the relay is in normal condition, thus forming a complete, closed-loop, adaptive intelligent diagnostic process.

[0055] In step S104, generating and outputting the final detection result based on the first or second detection result refers to the control unit generating the final diagnostic conclusion and outputting it through display, communication interface, or status lights, thereby completing the entire relay fault detection process. Complete fault diagnosis can be achieved through software algorithm logic, which greatly simplifies hardware design and saves costs.

[0056] In this embodiment, the control unit sends a first preset check command to the inverter and generates a first detection result or a second preset check command based on a first feedback signal. It further obtains a second feedback signal by executing the second preset check command, and finally generates and outputs the detection result. This method implements the detection logic by executing a pre-stored software program or firmware. It utilizes the characteristic of the open-circuit voltage rise of the current-source inverter, combined with its inherent overvoltage protection circuit status information as a feedback signal. This eliminates the need for an additional resistor sampling circuit, thus avoiding the additional losses and efficiency degradation associated with traditional detection methods. By judging the overvoltage protection trigger state and the real-time grid-connected power value, a complete closed-loop detection of relay open-circuit faults and sticking faults is achieved, forming a widely applicable adaptive intelligent diagnostic process. This reduces system complexity and hardware costs, avoids the fault risks of external detection circuits, and simplifies hardware design through software algorithms. While improving system reliability and safety, it maintains the inverter's high-efficiency power generation performance.

[0057] Please see Figure 2 In a further embodiment, the configuration of the first preset check command and the first feedback signal includes:

[0058] S201, the first preset check command is configured to control the relay to remain in the open state, and to control the inverter to perform grid connection operation according to the first preset power for a first preset time;

[0059] S202, the first feedback signal is configured as the status information of the overvoltage protection circuit, and the status information includes either the circuit on state or the circuit off state.

[0060] In step S201, the first preset check instruction is specifically configured to: control the relay to remain in the open state, or control the inverter to perform grid connection operation according to the first preset power and continue for the first preset time. This instruction is generated and issued by the inverter's control unit by executing a pre-stored software program or firmware. It is the starting action and control basis of the entire fault detection logic. Controlling the relay to remain in the open state means that the control unit actively issues an instruction to force the relay to be set to the open position, thereby artificially constructing a grid-side open circuit condition at the program level. Controlling the inverter to perform grid connection operation according to the first preset power and continue for the first preset time means that in this open circuit state, the inverter attempts to connect to the grid with power within the safety margin range. By utilizing the inherent characteristic that the output voltage of the current source inverter will rise sharply when the circuit is open, conditions that may trigger overvoltage protection are created.

[0061] In step S202, the first feedback signal is explicitly configured as the status information of the overvoltage protection circuit, which includes both circuit-on and circuit-off states. The overvoltage protection circuit refers to a hardware protection unit inherent within the inverter used for real-time monitoring of the bus voltage. When it detects a voltage value exceeding a preset safety threshold, it cuts off the drive or discharges energy to protect downstream circuits. Under open-circuit and low-power grid-connected conditions, if the relay normally disconnects, the voltage will inevitably surge and trigger the overvoltage protection, changing its state to the circuit-on state. If the relay fails to disconnect due to a sticking fault, the current source cannot form an open circuit, the voltage will not rise, and the overvoltage protection will remain in the circuit-off state. Therefore, the essence of the first feedback signal is to capture whether the overvoltage protection circuit has been triggered.

[0062] This embodiment configures the first preset check command to keep the relay in the open state and control the inverter to perform grid-connected operation according to the first preset power for a first preset time. At the same time, the first feedback signal is configured as the status information of the overvoltage protection circuit. Based on the inherent characteristic of the output voltage of the current source grid-connected inverter rising sharply when the circuit is open, the relay status is accurately detected by combining software command control with inherent protection hardware. No additional detection circuit is required, which completely eliminates the additional power consumption and efficiency loss caused by the traditional external sampling circuit. It avoids the risk of false alarms or missed alarms caused by the failure of the external detection circuit itself. While significantly reducing the system complexity and hardware cost, it effectively improves the reliability of the fault diagnosis function and the safety of the whole machine operation.

[0063] In some embodiments, the method further includes:

[0064] The state information is determined according to the first preset discrimination condition to obtain the first discrimination result. The first preset discrimination condition is configured to determine whether the overvoltage protection circuit is triggered.

[0065] A second preset check instruction is generated based on the first discrimination result;

[0066] Alternatively, generate and output the first detection result based on the first discrimination result.

[0067] In this embodiment, the first preset discrimination condition is configured to determine whether the overvoltage protection circuit is turned on. That is, by performing logical analysis on the state information of the overvoltage protection circuit, a preliminary judgment result about the relay state is obtained, namely the first discrimination result. When the control unit obtains the first feedback signal, it will call the preset discrimination condition to analyze the signal. If the first preset discrimination condition determines that the overvoltage protection circuit is in the turned-on state, it indicates that an open circuit was indeed formed when the relay should have been disconnected, and the voltage rise triggered the overvoltage protection circuit. At this time, the first discrimination result is that the relay is not stuck. The control unit will generate a second preset check instruction based on this result and enter the subsequent open circuit fault detection process.

[0068] In this embodiment, if the first preset discrimination condition determines that the overvoltage protection circuit is in the closed state, it indicates that although the program commands the relay to disconnect, the expected voltage rise and protection trigger are not detected. At this time, the first discrimination result is "relay suspected of sticking". Based on this discrimination result, the control unit can choose to directly generate and output the first detection result, determining that the relay has a sticking fault, or it can choose to generate a third preset inspection instruction containing further confirmation instructions to perform a second confirmation of the sticking fault, so as to improve the detection accuracy.

[0069] This embodiment determines the status information of the overvoltage protection circuit by configuring a first preset discrimination condition and obtaining a first discrimination result. Based on this discrimination result, a second preset inspection command is intelligently generated or the first detection result is directly output. This method is based on the inherent characteristic of the open-circuit voltage rise in current-source inverters. Through software algorithms, it intelligently analyzes the hardware protection signal, achieving automatic current diversion in the detection process and preliminary fault judgment. This design not only avoids unnecessary detection steps and improves detection efficiency, but also significantly enhances the accuracy and reliability of fault diagnosis through multiple discrimination mechanisms, while maintaining the advantage of not requiring external detection circuits, further optimizing the system response speed and intelligent detection level.

[0070] In some embodiments, if the status information is that the circuit is on, it indicates that the overvoltage protection circuit has been triggered, the first judgment result is normal, and a second preset check instruction is generated based on the first judgment result.

[0071] If the status information indicates that the circuit is off, it means that the overvoltage protection circuit has not been triggered. The first judgment result is an adhesion abnormality, and the first detection result is generated based on the first judgment result.

[0072] This embodiment uses an intelligent judgment mechanism based on the overvoltage protection circuit status information. When the status information indicates that the circuit is in the open state, it means that the overvoltage protection circuit has been triggered. According to the characteristics of the current source inverter, this indicates that when the relay is disconnected by program control, an effective open circuit state is indeed formed, causing the output voltage to rise to the protection threshold. At this time, the first judgment result is judged as normal, indicating that the relay has successfully executed the disconnection command and no sticking fault has occurred. Based on this normal judgment result, the control unit will generate a second preset check command.

[0073] In this embodiment, if the status information is "circuit off," it indicates that the overvoltage protection circuit has not been triggered. Given that the current source inverter should be in an open-circuit state, this situation suggests that the relay may have a sticking abnormality. In this case, the first judgment result is determined to be a sticking abnormality. Based on this abnormality judgment result, the control unit can directly generate and output the first detection result, determining that the relay has a sticking fault, thereby quickly completing the fault diagnosis.

[0074] This embodiment employs an intelligent judgment mechanism based on the overvoltage protection circuit status information. When the overvoltage protection circuit status information indicates an open circuit, the first judgment result is determined to be normal, and a second preset check command is generated. When the overvoltage protection circuit status information indicates a closed circuit, the first judgment result is determined to be an adhesion abnormality, and a first detection result is directly generated. This embodiment fully utilizes the voltage characteristics of the current source inverter in the open-circuit state. By establishing a correspondence between the trigger state of the overvoltage protection circuit and the actual state of the relay, it achieves rapid diagnosis of relay adhesion faults. This not only avoids the introduction of additional detection circuits, significantly reducing system complexity and hardware costs, but also greatly improves detection efficiency through the intelligent judgment mechanism. It can complete fault determination within milliseconds while maintaining high reliability and accuracy in the detection process, effectively improving the overall safety and response speed of the machine.

[0075] In some embodiments, if the status information is a circuit closed state, it indicates that the overvoltage protection circuit has not been triggered, the first determination result is an adhesion abnormality, and a third preset check instruction is generated based on the first determination result. The third preset check instruction is configured to control the relay to remain closed, then control the relay to remain open again, and control the inverter to perform grid connection operation according to the third preset power for a third preset time.

[0076] The method also includes:

[0077] Acquire a third feedback signal, which is configured as the status information of the overvoltage protection circuit after executing a third preset check command;

[0078] The status information of the overvoltage protection circuit after executing the third preset check command is determined based on the first preset discrimination condition, and the third discrimination result is obtained.

[0079] The third discrimination result is integrated with the first discrimination result to generate the first detection result and output it.

[0080] In this embodiment, when the status information indicates a circuit-off state, it means the overvoltage protection circuit has not been triggered, and the first judgment result is determined to be an adhesion abnormality. Based on this abnormality judgment, the system will further generate a third preset check instruction, which is configured to include three consecutive operations: first, control the relay to remain closed; then, control the relay to remain open again; and finally, control the inverter to perform grid connection operation according to a third preset power for a third preset time. This series of operations constitutes the confirmation and detection process for suspected adhesion faults.

[0081] This embodiment also includes a step of acquiring a third feedback signal, which is configured as the status information of the overvoltage protection circuit after executing a third preset check command. The system analyzes the status information according to the first preset discrimination condition to obtain a third discrimination result. Finally, the system integrates the third discrimination result with the previously obtained first discrimination result to generate and output the final first detection result.

[0082] This embodiment generates a third preset check command when the circuit is in a closed state. This command is configured to control the relay to close first and then open before performing grid-connection operation. A third feedback signal is acquired for secondary discrimination, and the third discrimination result is integrated with the first discrimination result to generate the final detection result. This scheme uses a multi-verification mechanism to confirm suspected adhesion faults. The operation of closing and then opening the relay eliminates occasional factors such as temporary poor contact, and reapplying the grid-connected power test ensures the stability of the detection conditions. While maintaining the advantage of not requiring an external detection circuit, this embodiment significantly improves the accuracy of fault diagnosis, avoids false alarms, enhances fault diagnosis accuracy through a secondary verification mechanism, and improves system reliability. It maintains stable detection performance even under complex operating conditions, providing a safer and more reliable relay status monitoring solution for grid-connected inverters.

[0083] In some embodiments, the first preset power is 0.5% to 2.0% of the rated value within the inverter's safety margin range;

[0084] The first preset time is 1 to 5 inverter switching cycles.

[0085] In this embodiment, the first preset power is limited to 0.5% to 2.0% of the inverter's rated value within its safety margin range. This parameter range is set based on the characteristics and safe operation requirements of the current source inverter. The lower limit of 0.5% ensures that the detection signal has sufficient strength to reliably generate a measurable electrical response, while the upper limit of 2.0% strictly limits the energy output during the detection process, ensuring that there is no risk of impact on the system or power grid. The setting of the first preset power limit range fully considers the compatibility of inverters with different capacities, ensuring both detection effectiveness and operational safety.

[0086] In this embodiment, the first preset time is limited to 1 to 5 inverter switching cycles. The shortest switching cycle of 1 ensures that it covers the minimum operating cycle of the inverter, while the longest switching cycle of 5 provides sufficient margin to prevent overvoltage protection circuit response delay, and avoids unnecessary energy loss that may be caused by excessively long duration. This time range design allows the detection process to reliably trigger the overvoltage protection mechanism while minimizing the detection time, significantly improving detection efficiency.

[0087] This embodiment constructs a detection parameter system by precisely limiting the first preset power to between 0.5% and 2.0% of the inverter's rated value within its safety margin range, and optimizing the first preset time to 1 to 5 switching cycles. The lower limit of 0.5% of the first preset power ensures the strength of the detection signal, while the upper limit of 2.0% eliminates the risk of system surges. Simultaneously, the extremely short time window of 1-5 switching cycles ensures reliable triggering of the overvoltage protection circuit while minimizing energy loss. This parameter configuration eliminates the additional losses associated with traditional detection methods, reduces the impact of the detection process on the system's power generation efficiency, and significantly improves the real-time performance of the detection response.

[0088] In some embodiments, the second preset check command is configured to control the relay to remain closed, and to control the inverter to perform grid connection operation at a second preset power for a second preset time.

[0089] The second feedback signal is configured to be the actual grid-connected power information.

[0090] In this embodiment, the second preset check command is specifically configured to control the relay to remain closed and to control the inverter to perform grid connection operation according to the second preset power for a second preset time. This command is a test command generated and issued by the control unit after the preliminary test is completed and it is determined that there is no sticking fault in the relay. Its purpose is to verify whether the relay can close normally, that is, to detect whether there is an open circuit fault.

[0091] In this embodiment, keeping the relay closed means driving the relay to the closed position through program instructions to establish a path for power transmission. Controlling the inverter to perform grid connection operation according to the second preset power means causing the inverter to output power to the grid side at the second preset power within the safety margin range. The duration of the second preset time limits the duration of the grid connection operation. The second preset time is usually set to 1-5 switching cycles to ensure the integrity of the detection while minimizing the detection time.

[0092] In this embodiment, the second feedback signal is configured as the actual grid-connected power information, that is, the actual output power value collected in real time by the power detection unit built into the inverter during the execution of the second preset check command. The second feedback signal reflects the actual power transmission under the theoretically closed state of the relay. This configuration fully utilizes another characteristic of the current source inverter: when the relay is normally closed, the inverter should be able to output stably according to the second preset power. If the relay has an open circuit fault, the actual output power will be significantly lower than the second preset power or even zero. By comparing the difference between the second preset power and the actual power, the system can accurately determine the closed state of the relay, thereby completing the reliable detection of open circuit faults.

[0093] This embodiment constructs a complete inverter open-circuit fault detection mechanism by configuring the second preset check command to control the relay to remain closed and control the inverter to perform grid-connected operation according to the second preset power for a second preset time, and configuring the second feedback signal to the actual grid-connected power information. It utilizes the inverter's built-in power detection unit to collect output power data in real time, and accurately determines the relay's closed state by comparing the difference between the second preset power and the actual power. Without adding additional detection circuitry, it achieves accurate diagnosis of relay open-circuit faults, reducing system complexity and hardware costs. Furthermore, the second preset time minimizes the impact of the detection process on system operation, while ensuring the reliability and accuracy of the detection results. This provides an efficient, economical, and reliable relay status monitoring solution for current-source grid-connected inverters.

[0094] In some embodiments, the control unit receives a second feedback signal and generates a second detection result based on the second feedback signal, including:

[0095] Calculate the power deviation between the actual grid-connected power and the second preset power;

[0096] The power deviation value is determined according to the second preset discrimination condition, and a second discrimination result is obtained. The second preset discrimination condition is configured to determine whether the power deviation value exceeds the preset deviation threshold range.

[0097] A second detection result is generated based on the second discrimination result.

[0098] In this embodiment, after receiving the second feedback signal, the control unit first calculates the power deviation between the actual grid-connected power and the second preset power. This calculation usually adopts a relative deviation algorithm, i.e. (actual power - set power) / set power × 100%. Then, the deviation value is judged according to the second preset discrimination condition. The second preset discrimination condition is configured to judge whether the power deviation value exceeds the preset deviation threshold range. The threshold range is usually set to ±5%, but can also be adjusted according to the specific application scenario. Finally, the corresponding second detection result is generated based on the second discrimination result obtained by the judgment.

[0099] In this embodiment, the power control characteristics of the current source inverter are fully utilized. When the relay is normally closed, the deviation between the actual output power and the set power is within the allowable range. If the relay has an open circuit fault or poor contact, the actual power will deviate significantly from the set value. By setting a reasonable deviation threshold, the system can accurately distinguish between normal operating conditions and fault states, thus avoiding misjudgment and ensuring the reliability of fault detection.

[0100] This embodiment calculates the power deviation between the actual grid-connected power and the second preset power after receiving the second feedback signal by the control unit. It then determines whether the deviation exceeds a preset deviation threshold based on a second preset discrimination condition, ultimately generating a second detection result. This embodiment uses a relative deviation algorithm to accurately calculate the power difference and achieves intelligent fault judgment through a configurable deviation threshold range, fully utilizing the power control characteristics of the current source inverter. This method achieves high-precision diagnosis of relay open-circuit faults without increasing hardware costs, improving detection accuracy. Furthermore, the flexibility of the software algorithm adapts to the characteristics of different inverter models, avoiding misjudgments caused by hardware differences and ensuring high reliability and adaptability of the detection process.

[0101] In some embodiments, if the power deviation value is within the range of a preset deviation threshold, the second discrimination result is normal;

[0102] If the power deviation value exceeds the preset deviation threshold range, the second judgment result is that the relay closure is abnormal;

[0103] A second detection result is generated based on the second discrimination result.

[0104] In this embodiment, when the power deviation value is within the preset deviation threshold range, the second discrimination result is determined to be normal. This indicates that the difference between the actual grid-connected power and the second preset power is within the allowable error range, the relay is in good closing condition, and can normally complete the power transmission function. Conversely, if the power deviation value exceeds the preset deviation threshold range, the second discrimination result is determined to be an abnormal relay closure. This situation indicates a significant difference between the actual output power and the second preset power, suggesting that the relay may have an open circuit fault or poor contact, resulting in obstructed power transmission.

[0105] In this embodiment, the control unit generates a corresponding second detection result based on the second discrimination result. When the discrimination result is normal, the control unit outputs a detection conclusion that the relay status is normal; when the discrimination result is that the relay closure is abnormal, the control unit outputs a detection result of an open circuit fault, and the fault information can be reported through the display interface or communication interface.

[0106] This embodiment generates a second judgment result by determining whether the power deviation value is within a preset deviation threshold range. When the deviation value is within the range, it is judged as normal; when it exceeds the range, it is judged as a relay closure malfunction, and a second detection result is generated accordingly. This embodiment utilizes a precise numerical comparison mechanism and sets a reasonable deviation threshold range to achieve intelligent diagnosis of the relay's operating status. This embodiment improves fault detection accuracy without increasing hardware costs, and its flexible software algorithm configuration can adapt to the characteristic requirements of different inverter models. It not only significantly reduces system complexity and maintenance costs but also achieves millisecond-level high-speed fault diagnosis, providing an economical, accurate, and responsive relay status detection solution for current-source grid-connected inverters, effectively ensuring the safe and stable operation of the system.

[0107] In some embodiments, the second preset power is 0.5% to 2.0% of the rated value within the inverter's safety margin range;

[0108] The second preset time is 1 to 5 inverter switching cycles.

[0109] In this embodiment, the second preset power is limited to 0.5% to 2.0% of the inverter's rated value within its safety margin range. The lower limit of 0.5% ensures that the detection signal has sufficient strength to produce a clear and identifiable electrical response, avoiding misjudgments due to weak signals. The upper limit of 2.0% strictly limits the energy output during the detection process, ensuring that even under the worst operating conditions, there will be no risk of impact on system components or the power grid. The second preset power range fully considers the compatibility of inverters with different capacities, ensuring both detection effectiveness and operational safety, while completely avoiding the efficiency loss caused by the additional sampling circuitry in traditional detection methods.

[0110] In this embodiment, the second preset time is limited to 1 to 5 inverter switching cycles. Limiting the second preset time to a minimum of 1 switching cycle ensures that the detection signal can fully cover the inverter's minimum operating cycle, guaranteeing the basic effectiveness of the detection; limiting the second preset time to a maximum of 5 switching cycles provides sufficient time margin to prevent overvoltage protection circuit response delays, while avoiding unnecessary energy loss that might result from excessively long durations. The design of the second preset time allows the detection process to reliably assess the power transmission status while compressing the detection time, thus improving detection efficiency.

[0111] This embodiment constructs a highly efficient and reliable detection parameter system by limiting the second preset power within the inverter's safety margin and optimizing the second preset time to 1 to 5 switching cycles. This embodiment ensures the detection signal strength by using a 0.5% lower limit for the second preset power and eliminates system surge risks by using a 2.0% upper limit for the second preset power. Simultaneously, the extremely short time window of 1-5 switching cycles ensures detection integrity while minimizing energy loss. This precise parameter configuration enables the detection process to operate at low power while maintaining high reliability, completely eliminating the additional losses associated with traditional detection methods. It reduces the impact of the detection process on the system's power generation efficiency to a negligible level, while significantly improving the real-time performance of the detection response. This provides a highly versatile, safe, and optimized detection scheme for current-source grid-connected inverters of different capacity specifications, without affecting normal power generation performance.

[0112] Please see Figure 3 To facilitate understanding, the following examples are provided to further illustrate the aforementioned content:

[0113] The existing technology has the following problems:

[0114] 1. Existing relay fault detection methods and patents typically require additional measures such as resistance sampling circuits and optocoupler sampling circuits for the relay section, which are complex and costly to implement.

[0115] 2. The additional resistor sampling circuit will increase losses, reduce the inverter's power generation efficiency, and make it impractical.

[0116] Furthermore, this embodiment provides a method for detecting internal relay faults in a current-source grid-connected inverter as follows:

[0117] 1. Set the grid-connected power P1. The value of P1 can be determined according to the inverter capacity. Within the safety margin, select 1%Pn.

[0118] 2. Set the grid connection time t1. The selection of t1 is based on the inverter switching frequency. Set t1 to 1-5 switching cycles, which is sufficient to trigger the internal hardware overvoltage protection circuit.

[0119] 3. Start the grid connection program, check whether the internal hardware overvoltage protection is triggered during the grid connection process, and shut down the grid connection program after time t1 is reached.

[0120] Determine whether the hardware overvoltage protection in the first step has been triggered, and trigger the following steps based on the result:

[0121] 1. Hardware overvoltage protection is triggered:

[0122] Since it is a current-source inverter, the downstream relays have been disconnected via the program, and the downstream circuit is in an open-circuit state. When the grid connection program is activated, the bus voltage rises, exceeding the inverter's internal overvoltage protection point, triggering the hardware overvoltage protection. This indicates that the relay state at this time is consistent with the program control state, and the relay has not experienced a sticking fault. Next, the relay open-circuit fault detection program is activated to continue detecting whether the relay is in an open-circuit state. The following is the relay open-circuit fault detection program.

[0123] a. Close the relay.

[0124] b. Set the grid-connected power P1. The value of P1 can be determined according to the inverter capacity. Within the safety margin, select 1%Pn.

[0125] c. Set the grid connection time t1. The selection of t1 is based on the inverter switching frequency, and t1 is set to 1-5 switching cycles.

[0126] d. Start the grid connection program. During the grid connection process, check whether the grid connection function is normal and whether the difference ΔP between the grid connection power P and the set power P1 is within the allowable range. For example, ΔP ≤ 5%.

[0127] e. If ΔP≤5%, it is considered that the grid connection status is normal, the relay status is normal, and no open circuit fault has occurred.

[0128] f. If P1=0, then the relay is determined to be unable to close normally and is in an open circuit fault state.

[0129] 2. Hardware overvoltage protection was not triggered:

[0130] Since this is a current-source inverter, the downstream relays have been disconnected via the program, and the downstream circuit is in an open-circuit state. If the bus hardware overvoltage protection is not triggered after the grid connection program is started, it indicates that the relays may be stuck. Continue to execute the following relay sticking fault detection program.

[0131] a. Close the relay.

[0132] b. Set the grid-connected power P1. The value of P1 can be determined according to the inverter capacity. Within the safety margin, select 1%Pn.

[0133] c. Start the grid connection program, disconnect the relay during the grid connection process, and detect the grid connection power value P after the relay is disconnected.

[0134] d. If P>0, then the relay is determined to be in a sticking fault state.

[0135] e. If P=0, then it is determined that the relay sticking fault has been resolved and the relay is in normal condition.

[0136] This embodiment has the following beneficial effects:

[0137] 1. No additional external detection circuits for relays are required. Relay fault detection can be achieved by relying on the hardware protection function built into the inverter itself, combined with software logic.

[0138] 2. Optimized the efficiency loss and cost increase caused by adding extra sampling circuits for relay detection in other patents.

[0139] Unlike existing technologies, the above technical solution involves the control unit sending a first preset check command to the inverter and receiving a first feedback signal generated after its execution, thereby generating a first detection result or a second preset check command. In subsequent processes, a second feedback signal is obtained based on the execution result of the second preset check command, and a second detection result is generated, ultimately outputting a comprehensive detection result. This method fully utilizes the inherent characteristics of the current-source grid-connected inverter and existing hardware overvoltage protection circuits, implementing relay open-circuit and sticking fault detection through software logic without the need for any additional external detection circuits. This design significantly reduces system complexity and cost, completely eliminates the additional power consumption caused by traditional sampling resistors, helps maintain the inverter's high-efficiency power generation performance, and avoids false alarms or missed alarms caused by faults in the additional detection circuits themselves, greatly improving the reliability of fault diagnosis functions and the overall operational safety of the unit.

[0140] Finally, it should be noted that although the above embodiments have been described in the text and drawings of this application, this should not limit the scope of patent protection of this application. Any technical solutions that are based on the essential concept of this application and utilize the content described in the text and drawings of this application, resulting in equivalent structural or procedural substitutions or modifications, as well as the direct or indirect application of the technical solutions of the above embodiments to other related technical fields, are all included within the scope of patent protection of this application.

Claims

1. A current-source type grid-connected inverter internal relay fault detection method, characterized by, Applicable to inverters, wherein the inverters are equipped with relays and overvoltage protection circuits, the detection method includes: The control unit sends a first preset check command to the inverter; The inverter receives and executes the first preset check command; A first feedback signal is generated based on the inverter's execution result, and the first feedback signal is sent to the control unit; The control unit receives the first feedback signal and generates a first detection result based on the first feedback signal; Alternatively, the control unit receives the first feedback signal, generates a second preset check command based on the first feedback signal, and sends it to the inverter; The inverter receives and executes the second preset check command; Acquire the second feedback signal generated according to the execution process of the inverter and send it to the control unit; The control unit receives the second feedback signal and generates a second detection result based on the second feedback signal; The final detection result is generated and output based on the first or second detection result; The first preset check command is configured to control the relay to remain in the open state, and to control the inverter to perform grid connection operation according to the first preset power for a first preset time. The first feedback signal is configured as the status information of the overvoltage protection circuit, and the status information includes either the circuit on state or the circuit off state. The second preset check command is configured to control the relay to remain closed, and to control the inverter to perform grid connection operation at a second preset power for a second preset time. The second feedback signal is configured as the actual grid-connected power information.

2. The current-source type grid-connected inverter internal relay fault detection method according to claim 1, characterized by, The method further includes: The state information is determined according to the first preset discrimination condition to obtain the first discrimination result. The first preset discrimination condition is configured to determine whether the overvoltage protection circuit is turned on. A second preset inspection instruction is generated based on the first discrimination result; Alternatively, a first detection result can be generated and output based on the first discrimination result.

3. The current-source type grid-connected inverter internal relay fault detection method according to claim 2, characterized by, If the status information indicates that the circuit is open, it means that the overvoltage protection circuit has been triggered, the first judgment result is normal, and a second preset check instruction is generated based on the first judgment result. If the status information indicates that the circuit is off, it means that the overvoltage protection circuit has not been triggered, the first judgment result is an adhesion abnormality, and the first detection result is generated based on the first judgment result.

4. The current-source type grid-connected inverter internal relay fault detection method according to claim 2, characterized by, If the status information is a circuit closed state, it indicates that the overvoltage protection circuit has not been triggered. The first judgment result is an adhesion abnormality. A third preset check instruction is generated based on the first judgment result. The third preset check instruction is configured to control the relay to remain closed, then control the relay to remain open again, and control the inverter to perform grid connection operation according to the third preset power for a third preset time. The method further includes: Acquire a third feedback signal, which is configured as the status information of the overvoltage protection circuit after executing a third preset check command; Based on the first preset discrimination condition, the state information of the overvoltage protection circuit after executing the third preset check instruction is determined, and the third discrimination result is obtained; The third discrimination result is integrated with the first discrimination result to generate the first detection result and then output.

5. The method for detecting internal relay faults in a current-source grid-connected inverter according to claim 1, characterized in that, The first preset power is 0.5% to 2.0% of the rated value within the inverter's safety margin range; The first preset time is 1 to 5 inverter switching cycles.

6. The method for detecting internal relay faults in a current-source grid-connected inverter according to claim 1, characterized in that, The control unit receives the second feedback signal and generates a second detection result based on the second feedback signal, including: Calculate the power deviation between the actual grid-connected power and the second preset power; The power deviation value is determined according to the second preset discrimination condition to obtain the second discrimination result. The second preset discrimination condition is configured to determine whether the power deviation value exceeds the preset deviation threshold range. The second detection result is generated based on the second discrimination result.

7. The method for detecting internal relay faults in a current-source grid-connected inverter according to claim 6, characterized in that, If the power deviation value is within the preset deviation threshold range, then the second discrimination result is normal; If the power deviation value exceeds the preset deviation threshold range, the second judgment result is that the relay closure is abnormal; The second detection result is generated based on the second discrimination result.

8. The method for detecting internal relay faults in a current-source grid-connected inverter according to claim 1, characterized in that, The second preset power is 0.5% to 2.0% of the rated value within the inverter's safety margin range; The second preset time is 1 to 5 inverter switching cycles.

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