Open-circuit fault detection circuit and open-circuit fault detection method

Abstract

The application discloses an open-circuit fault detection circuit and an open-circuit fault detection method. The open-circuit fault detection circuit controls an inverter circuit and a live wire relay according to a driving instruction, generates different comparison conditions and driving instructions according to an inverter-side phase voltage and a grid-side phase voltage, and can select a suitable comparison condition according to the connection state between the inverter-side zero line and the grid-side zero line to determine whether the live wire relay has an open-circuit fault. Compared with using a single comparison condition to determine the open-circuit fault of the live wire relay under different connection states, the open-circuit fault detection circuit can reduce the difficulty of threshold setting when the inverter-side zero line and the grid-side zero line are not shared, and can shorten the detection time of the open-circuit fault when the inverter-side zero line and the grid-side zero line are shared, so that the open-circuit fault detection of the live wire relay under the two conditions of zero line sharing and non-sharing can be realized quickly, accurately and reliably without additional hardware circuit.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to an open-circuit fault detection circuit and an open-circuit fault detection method. Background Technology

[0002] For grid-connected systems such as photovoltaic inverters and energy storage converters, before grid connection, it is necessary to use software to detect whether there is an open circuit fault in the AC relays using a sampling circuit. For open circuit faults in relays in grid-connected systems, the difference between the inverter-side voltage and the grid-side voltage is generally detected. If it exceeds a preset threshold, the relay is considered to have an open circuit fault.

[0003] However, when the inverter-side neutral line and the grid-side neutral line are not shared, this detection method is difficult to set and may result in misjudgment. When the inverter-side neutral line and the grid-side neutral line are shared, the detection time for open circuit faults is long. For systems that need to respond to power immediately after grid connection, untimely detection of open circuit faults often leads to dangers such as hardware overcurrent. Summary of the Invention

[0004] This application provides an open-circuit fault detection circuit and an open-circuit fault detection method to alleviate the above-mentioned technical problems.

[0005] In a first aspect, this application provides an open-circuit fault detection circuit, which includes an inverter circuit, a live wire relay, a common control unit, a driver, a sampling module, and a controller. The inverter circuit is connected to the AC power grid in sequence through the inverter-side live wire, the live wire relay, and the grid-side live wire. The inverter circuit is also connected to the AC power grid in sequence through the inverter-side neutral wire, the common control unit, and the grid-side neutral wire. The common control unit is used to control the connection state between the inverter-side neutral wire and the grid-side neutral wire. The driver is connected to the inverter circuit and the live wire relay, and is used to control the inverter circuit and the live wire relay according to the drive command. The sampling module is connected to the inverter circuit and the AC power grid, and is used to collect the inverter-side phase voltage and the grid-side phase voltage. The controller is connected to the driver and the sampling module, and is used to generate different comparison conditions and drive commands based on the inverter-side phase voltage and the grid-side phase voltage, and select the comparison condition according to the connection state to determine whether there is an open-circuit fault in the live wire relay.

[0006] Secondly, this application also provides an open-circuit fault detection method. This method is applied to an open-circuit fault detection circuit, which includes an inverter circuit, a live wire relay, and a common control unit. The inverter circuit is connected to the AC power grid sequentially through the inverter-side live wire, the live wire relay, and the grid-side live wire. The inverter circuit is also connected to the AC power grid sequentially through the inverter-side neutral wire, the common control unit, and the grid-side neutral wire. The common control unit controls the connection state between the inverter-side neutral wire and the grid-side neutral wire. The open-circuit fault detection method includes: controlling the inverter circuit and the live wire relay with drive commands; acquiring the inverter-side phase voltage and the grid-side phase voltage; generating different comparison conditions and drive commands based on the inverter-side phase voltage and the grid-side phase voltage; and selecting the comparison condition based on the connection state to determine whether the live wire relay has an open-circuit fault.

[0007] The open-circuit fault detection circuit and method provided in this application control the inverter circuit and the live wire relay according to the drive command. Different comparison conditions and drive commands are generated based on the inverter side phase voltage and the grid side phase voltage. The appropriate comparison condition can be selected according to the connection state between the inverter side neutral wire and the grid side neutral wire to determine whether there is an open-circuit fault in the live wire relay. Compared with using a single comparison condition to judge the open-circuit fault of the live wire relay under different connection states, this method can reduce the difficulty of threshold setting when the inverter side neutral wire and the grid side neutral wire are not shared, and shorten the detection time of open-circuit fault when the inverter side neutral wire and the grid side neutral wire are shared. Thus, it can quickly, accurately and reliably realize the open-circuit fault detection of the live wire relay under both shared and non-shared neutral wire conditions without the need for additional hardware circuitry. Attached Figure Description

[0008] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0009] Figure 1 This is a first circuit schematic diagram of an open-circuit fault detection circuit provided in an embodiment of this application.

[0010] Figure 2 This is a second circuit schematic diagram of the open-circuit fault detection circuit provided in the embodiments of this application.

[0011] Figure 3 This is a third circuit schematic diagram of the open-circuit fault detection circuit provided in the embodiments of this application.

[0012] Figure 4 This is a fourth circuit schematic diagram of the open-circuit fault detection circuit provided in the embodiments of this application.

[0013] Figure 5 This is a flowchart illustrating the open-circuit fault detection method provided in an embodiment of this application. Detailed Implementation

[0014] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0015] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Features thus defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0016] For grid-connected systems such as photovoltaic inverter circuits and energy storage converters, before grid connection, it is necessary to use software to detect whether there is an open circuit fault in the AC relays, in conjunction with the sampling circuit. For open circuit faults in relays in grid-connected systems, the difference between the inverter-side voltage and the grid-side voltage is generally detected. If it exceeds a preset threshold, the relay is considered to have an open circuit fault.

[0017] However, when the inverter-side neutral line and the grid-side neutral line are not shared, this detection method is difficult to set and may result in misjudgment. When the inverter-side neutral line and the grid-side neutral line are shared, the detection time for open circuit faults is long. For systems that need to respond to power immediately after grid connection, untimely detection of open circuit faults often leads to dangers such as hardware overcurrent.

[0018] To address the aforementioned issues, this application reserves sufficient downtime at the moment the grid-connected relay engages. During this downtime, the grid clamping is used to detect the zero-crossing state of the inverter-side voltage. This approach eliminates the need for additional hardware circuitry, thus providing a quick, accurate, and reliable solution to the problems.

[0019] This embodiment provides an open-circuit fault detection circuit, such as Figure 1As shown, the open-circuit fault detection circuit includes an inverter circuit 10, a live wire relay 20, a common control unit 30, a driver 40, a sampling module 50, and a controller 60. The inverter circuit 10 is connected to the AC power grid Grid via the inverter-side live wire IL, the live wire relay 20, and the grid-side live wire. The inverter circuit 10 is also connected to the AC power grid Grid via the inverter-side neutral wire n, the common control unit 30, and the grid-side neutral wire N. The common control unit 30 controls the connection status between the inverter-side neutral wire n and the grid-side neutral wire N. The driver 40 is connected to the inverter circuit 10 and the live wire relay 20, and is used to control the inverter circuit 10 and the live wire relay 20 according to drive commands. The sampling module 50 is connected to the inverter circuit 10 and the AC power grid Grid, and is used to collect the inverter-side phase voltages Van to Vcn and the grid-side phase voltages VAN to VCN. The controller 60 is connected to the driver 40 and the sampling module 50. The controller 60 is used to generate different comparison conditions and drive commands based on the inverter side phase voltage Van~Vcn and the grid side phase voltage VAN~VCN, and select the comparison condition according to the connection status to determine whether the live wire relay 20 has an open circuit fault.

[0020] It is understood that the open-circuit fault detection circuit provided in this embodiment controls the inverter circuit 10 and the live wire relay 20 according to the drive command. It generates different comparison conditions and drive commands based on the inverter side phase voltage Van~Vcn and the grid side phase voltage VAN~VCN. It can select a suitable comparison condition according to the connection state between the inverter side neutral line n and the grid side neutral line N to determine whether the live wire relay 20 has an open-circuit fault. Compared with using a single comparison condition to determine the open-circuit fault of the live wire relay 20 under different connection states, it can reduce the difficulty of threshold setting when the inverter side neutral line n and the grid side neutral line N are not shared, and shorten the detection time of open-circuit fault when the inverter side neutral line n and the grid side neutral line N are shared. Thus, it can quickly, accurately and reliably realize the open-circuit fault detection of the live wire relay 20 under the two conditions of shared and unshared neutral lines without adding additional hardware circuits.

[0021] It should be noted that the inverter-side phase voltages Van to Vcn include the first inverter-side phase voltage (Van), the second inverter-side phase voltage (Vbn), and the third inverter-side phase voltage (Vcn). The grid-side phase voltages VAN to VCN include the first grid-side phase voltage (VAN), the second grid-side phase voltage (VBN), and the third grid-side phase voltage (VCN).

[0022] In some embodiments, such as Figure 2As shown, when the shared control unit 30 is the neutral wire relay S4 connected to the driver 40, the neutral wire relay S4 is used to control the connection state. Alternatively, the shared control unit 30 is used to control the inverter-side neutral wire n to be directly connected to the grid-side neutral wire N, or to control the inverter-side neutral wire n to be disconnected from the grid-side neutral wire N.

[0023] It should be noted that the connection status between the inverter-side neutral line n and the grid-side neutral line N includes the following three forms:

[0024] The first type, or type 1, controls the connection state through the neutral relay S4. For example, when the contacts of the neutral relay S4 are open, the connection state is open; or, when the contacts of the neutral relay S4 are closed, the connection state is closed.

[0025] The second form, type 2, is to keep the connection in a disconnected state by making the inverter side neutral line n unconnected to the grid side neutral line N.

[0026] The third form, type 3, is to connect the inverter-side neutral line n to the grid-side neutral line N, so that the connection is always in a conductive state.

[0027] When the inverter-side neutral line n is connected to the grid-side neutral line N, it means that the inverter circuit 10 and the AC grid share the neutral line; when the inverter-side neutral line n is not connected to the grid-side neutral line N, it means that the inverter circuit 10 and the AC grid do not share the neutral line.

[0028] In some embodiments, such as Figure 1 As shown, the inverter-side live wire IL includes the inverter-side first phase wire IL1, the inverter-side second phase wire IL2, and the inverter-side third phase wire IL3. The grid-side live wire includes the grid-side first phase wire GL1, the grid-side second phase wire GL2, and the grid-side third phase wire GL3. The live wire relay 20 includes at least one relay group connected in series between the inverter-side live wire IL and the grid-side live wire. Each relay group includes a first relay S1, a second relay S2, and a third relay S3. The first relay S1 is used to control the connection state between the inverter-side first phase wire IL1 and the grid-side first phase wire GL1. The second relay S2 is used to control the connection state between the inverter-side second phase wire IL2 and the grid-side second phase wire GL2. The third relay S3 is used to control the connection state between the inverter-side third phase wire IL3 and the grid-side third phase wire GL3.

[0029] It should be noted that the number of relay groups can be one or more. When there are multiple relay groups, different relay groups can be connected in series to meet different safety requirements. Specifically, the inverter-side first phase line IL1, inverter-side second phase line IL2, and inverter-side third phase line IL3 can be, in sequence, inverter-side phase a, inverter-side phase b, and inverter-side phase c. The grid-side first phase line GL1, grid-side second phase line GL2, and grid-side third phase line GL3 can be, in sequence, grid-side phase A, grid-side phase B, and grid-side phase C.

[0030] In some embodiments, such as Figure 2 As shown, the open-circuit fault detection circuit also includes a first inductor L1, a second inductor L2, a third inductor L3, a first capacitor C1, a second capacitor C2, and a third capacitor C3. The first inductor L1 is connected to the first phase line IL1 on the inverter side. The second inductor L2 is connected to the second phase line IL2 on the inverter side. The third inductor L3 is connected to the third phase line IL3 on the inverter side. The first terminal of the first capacitor C1 is connected to the first inductor L1 and the first relay S1. The first terminal of the second capacitor C2 is connected to the second inductor L2 and the third relay S3. The first terminal of the third capacitor C3 is connected to the third inductor L3 and the third relay S3, and the second terminal of the third capacitor C3 is connected to the second terminal of the first capacitor C1, the second terminal of the second capacitor C2, and the neutral line n on the inverter side.

[0031] It should be noted that the first inductor L1, the second inductor L2, the third inductor L3, the first capacitor C1, the second capacitor C2, and the third capacitor C3 can constitute an inverter-side LC filter. This LC filter filters the inverter-side AC power, reducing high-order harmonics and noise interference. This makes the sampling of the inverter-side phase voltages Van to Vcn more stable and accurate, providing a clean input signal for subsequent zero-crossing cycle or RMS value calculations, thereby improving the accuracy and reliability of fault detection.

[0032] In some embodiments, such as Figure 3 As shown, the open-circuit fault detection circuit also includes a fourth inductor L4, a fifth inductor L5, a sixth inductor L6, a fourth capacitor C4, a fifth capacitor C5, and a sixth capacitor C6. The fourth inductor L4 is connected to the first phase line GL1 on the grid side. The fifth inductor L5 is connected to the second phase line GL2 on the grid side. The sixth inductor L6 is connected to the third phase line GL3 on the grid side. The first terminal of the fourth capacitor C4 is connected to the fourth inductor L4 and the AC power grid. The first terminal of the second capacitor C2 is connected to the fifth inductor L5 and the AC power grid. The first terminal of the third capacitor C3 is connected to the sixth inductor L6 and the AC power grid. The second terminal of the sixth capacitor C6 is connected to the second terminals of the fourth capacitor C4, the fifth capacitor C5, and the grid-side neutral line N.

[0033] It should be noted that the fourth inductor L4, the fifth inductor L5, the sixth inductor L6, the fourth capacitor C4, the fifth capacitor C5, and the sixth capacitor C6 can form a grid-side LC filter. This filter filters the grid-side AC power, smoothing out grid voltage fluctuations and noise. This makes the sampling of grid-side phase voltages VAN to VCN smoother and more reliable, providing a reference value for calculating time and voltage thresholds, ensuring the accuracy of reference values ​​for comparison conditions (such as zero-crossing cycles or RMS values), and reducing the risk of misjudgment.

[0034] In some embodiments, such as Figure 4 The proposed scheme combines... Figure 2 and Figure 3 The proposed solution incorporates both inverter-side and grid-side LC filters, achieving dual optimization of AC power quality through the simultaneous use of these filters. The inverter-side LC filter purifies the output voltage of the inverter circuit 10, while the grid-side LC filter stabilizes the grid input voltage. This results in more consistent and lower-noise voltage sampling across the entire system, providing a high-quality data source for fault detection and further enhancing detection accuracy and anti-interference capabilities.

[0035] In some embodiments, after the open-circuit fault detection circuit is powered on, the controller 60 keeps the live wire relay 20 in the open state through the driver 40. After the inverter-side phase voltages Van to Vcn exceed the grid-side voltage reference value, the controller 60 controls the inverter circuit 10 to stop transmitting waves for a preset time period and controls the live wire relay 20 to be turned on through the driver 40. During the preset time period, the controller 60 calculates the zero-crossing period and RMS value of the inverter-side phase voltages Van to Vcn, and the time threshold and voltage threshold of the grid-side phase voltages VAN to VCN.

[0036] It should be noted that by reserving a pause time (stopping the inverter circuit 10 from generating waves) at the moment the live wire relay 20 is activated, and by utilizing the clamping effect of the AC grid to detect changes in the inverter-side phase voltages Van to Vcn, the system can quickly calculate key parameters (such as zero-crossing cycle and RMS value) within the pause window. This reduces detection delay and is especially suitable for systems that require immediate power response after grid connection, avoiding hardware overcurrent hazards caused by untimely detection.

[0037] In some embodiments, the comparison conditions include a first condition and a second condition. The first condition is whether the zero-crossing period exceeds a time threshold, and the second condition is whether the effective values ​​of the inverter-side phase voltages Van to Vcn exceed a voltage threshold.

[0038] It should be noted that by sampling two different comparison conditions, the system can flexibly select the judgment criterion based on the connection status. This optimizes the application of thresholds, prioritizing the use of zero-crossing cycles to accelerate detection under common-zero-wire conditions, and prioritizing the use of valid values ​​to simplify threshold settings under non-common-zero-wire conditions, thereby improving the overall efficiency and accuracy of detection.

[0039] Table 1:

[0040] Operating conditions The logic that works Shared neutral wire: S4 in type 1 or type 3 Determine if the zero-crossing cycle exceeds the threshold. Not sharing a neutral wire: S4 is disconnected in type 1 or type 2 Determine if the valid value exceeds the threshold.

[0041] Table 1 shows the specific details: When a shared neutral wire is used, this can be achieved by engaging the neutral wire relay S4 in type 1 or by using type 3. In this case, the open-circuit judgment logic is: the first condition is whether the zero-crossing cycle exceeds the threshold. When a shared neutral wire is not used, this can be achieved by disengaging the neutral wire relay S4 in type 1 or by using type 2. In this case, the open-circuit judgment logic is: the second condition is whether the effective value exceeds the threshold.

[0042] In some embodiments, when the connection state is on, the controller 60 selects a first condition to determine whether the live wire relay 20 has an open circuit fault.

[0043] It should be noted that when the inverter-side neutral line n and the grid-side neutral line N share a neutral line, using zero-crossing cycle comparison as the criterion directly reflects voltage synchronization. Since the grid clamping effect is more pronounced when sharing a neutral line, zero-crossing cycle deviation can quickly indicate open-circuit faults, thereby shortening detection time and improving response speed.

[0044] In some embodiments, when the zero-crossing period of the inverter-side phase voltages Van to Vcn exceeds a time threshold, the controller 60 determines that the live wire relay 20 corresponding to the inverter-side phase voltages Van to Vcn has an open-circuit fault. Alternatively, when the zero-crossing period of the inverter-side phase voltages Van to Vcn is within the upper or lower limit of the time threshold, the controller 60 determines that the live wire relay 20 corresponding to the inverter-side phase voltages Van to Vcn does not have an open-circuit fault.

[0045] It should be noted that by comparing the zero-crossing period with a time threshold (e.g., reporting a fault if it exceeds the threshold, and judging it as normal if it is within the range), the system can reliably determine the voltage based on the periodic changes at the zero-crossing point under common-line operating conditions. The zero-crossing period, as a dynamic indicator, can capture voltage asynchrony caused by relay open circuits, reducing false alarms and ensuring accurate detection results.

[0046] In some embodiments, when the connection is disconnected, the controller 60 selects a second condition to determine whether the fire wire relay 20 has an open circuit fault.

[0047] It should be noted that in the disconnected state where the inverter-side neutral line n and the grid-side neutral line N are not shared, the effective value comparison is chosen as the judgment condition to avoid the difficulty in setting the threshold during the zero-crossing cycle when the neutral lines are not shared. As a steady-state voltage indicator, the effective value can reliably reflect the voltage deviation caused by the open circuit, simplifying the detection logic and improving robustness under the condition of not sharing neutral lines.

[0048] In some embodiments, when the effective value of the inverter-side phase voltages Van to Vcn exceeds the voltage threshold, the controller 60 determines that the live wire relay 20 corresponding to the inverter-side phase voltages Van to Vcn has an open circuit fault. Alternatively, when the effective value of the inverter-side phase voltages Van to Vcn is within the upper or lower limit range of the voltage threshold, the controller 60 determines that the live wire relay 20 corresponding to the inverter-side phase voltages Van to Vcn does not have an open circuit fault.

[0049] It should be noted that by comparing the effective values ​​of the inverter-side phase voltages Van to Vcn with voltage thresholds (if they exceed the threshold, a fault is reported; if they are within the range, normal operation is determined), the system can use the stable parameter of the effective value for judgment under non-shared neutral line conditions. The deviation of the effective value directly indicates that the voltage is not clamped by the grid, thereby reliably identifying open-circuit faults and reducing false alarms caused by threshold ambiguity.

[0050] In some embodiments, the grid-side voltage reference value is greater than or equal to the difference between the grid-side phase voltages VAN-VCN and a first voltage threshold, and less than or equal to the sum of the grid-side phase voltages VAN-VCN and the first voltage threshold. The time threshold of the grid-side phase voltages VAN-VCN is greater than or equal to a first percentage of half a grid cycle of the AC grid, and less than or equal to a second percentage of half a grid cycle of the AC grid, wherein the first percentage is less than 1 and the second percentage is greater than 1. The voltage threshold of the grid-side phase voltages VAN-VCN is greater than or equal to a third percentage of the effective value of the grid-side phase voltages VAN-VCN, and less than or equal to a fourth percentage of the effective value of the grid-side phase voltages VAN-VCN, wherein the third percentage is less than 1 and the fourth percentage is greater than 1. The zero-crossing period of the inverter-side phase voltages Van-Vcn is obtained based on a preset duration, the grid cycle, and the number of zero-crossings of the grid-side phase voltages VAN-VCN.

[0051] It should be noted that by setting parameter ranges (such as the grid-side voltage reference value being based on the sum / difference of the grid-side phase voltages VAN~VCN and a threshold, the time threshold being based on a percentage of the grid cycle, and the voltage threshold being based on a percentage of the effective values ​​of the grid-side phase voltages VAN~VCN), the system can adapt to grid fluctuations (such as voltage or frequency changes). The zero-crossing cycle calculation, combined with preset duration, grid cycle, and number of zero-crossings, ensures that the parameters are reasonable and adjustable, improving the robustness and reliability of the detection conditions and preventing grid anomalies from interfering with the detection results.

[0052] For example, when detecting an open-circuit fault in the first relay S1, the grid-side voltage reference value can be obtained based on the first grid-side phase voltage VAN between the grid-side first phase line GL1 and the grid-side neutral line N, and the first voltage threshold.

[0053] The first percentage can be 95%, and the second percentage can be 105%, which means the time threshold is any value within the range of (Tgrid / 2) ± 5%, where Tgrid is the grid cycle of the AC grid.

[0054] The third percentage can be 95%, the fourth percentage can be 105%, and the voltage threshold of the grid-side phase voltages VAN to VCN is any value within the range of Vgrid ± 5%, where Vgrid is the effective value of the corresponding phase voltage in the grid-side phase voltages VAN to VCN.

[0055] The zero-crossing period (ta / tb / tc) of the inverter-side phase voltages Van to Vcn is calculated as follows:

[0056]

[0057] Where Ts represents the switching period, and Y represents the number of zero-crossings of the grid-side phase voltages VAN to VCN.

[0058] In some embodiments, this embodiment also provides an open-circuit fault detection method, which is applied to the open-circuit fault detection circuit described above. The open-circuit fault detection method includes: controlling the inverter circuit 10 and the live-wire relay 20 with drive commands; acquiring the inverter-side phase voltages Van~Vcn and the grid-side phase voltages VAN~VCN; generating different comparison conditions and drive commands based on the inverter-side phase voltages Van~Vcn and the grid-side phase voltages VAN~VCN; and selecting the comparison condition according to the connection status to determine whether the live-wire relay 20 has an open-circuit fault.

[0059] It is understood that the open-circuit fault detection method provided in this embodiment can also control the inverter circuit 10 and the live wire relay 20 according to the drive command, and generate different comparison conditions and drive commands according to the inverter side phase voltage Van~Vcn and the grid side phase voltage VAN~VCN. It can select a suitable comparison condition according to the connection state between the inverter side neutral line n and the grid side neutral line N to determine whether the live wire relay 20 has an open-circuit fault. Compared with using a single comparison condition to determine the open-circuit fault of the live wire relay 20 under different connection states, it can reduce the difficulty of threshold setting when the inverter side neutral line n and the grid side neutral line N are not shared, and shorten the detection time of open-circuit fault when the inverter side neutral line n and the grid side neutral line N are shared. Thus, it can quickly, accurately and reliably realize the open-circuit fault detection of the live wire relay 20 under the two conditions of shared and unshared neutral lines without adding additional hardware circuits.

[0060] In some embodiments, such as Figure 5 As shown, the open-circuit fault detection method also includes the following:

[0061] Power-on: The open circuit fault detection circuit starts to power on.

[0062] Inverter circuit 10 emits a wave: In response to the power-on of the open-circuit fault detection circuit, the inverter circuit 10 emits a wave.

[0063] Detecting inverter-side phase voltages Van~Vcn and grid-side phase voltages VAN~VCN: The grid-side voltage reference value can be obtained through the grid-side phase voltages VAN~VCN.

[0064] VAN-threshold (first voltage threshold) ≤ Van ≤ VAN+threshold (first voltage threshold): Van is the first inverter-side phase voltage Van~Vcn, and the range of the grid-side voltage reference value is VAN±threshold (first voltage threshold).

[0065] When the inverter-side phase voltage Van to Vcn is within the range of the grid-side voltage reference value, continue to determine whether VAN-threshold (first voltage threshold) ≤ Van ≤ VAN+threshold (first voltage threshold) holds true.

[0066] Engaging S1, S2, and S3: When the inverter-side phase voltage Van to Vcn exceeds the grid-side voltage reference value, the inverter circuit 10 is controlled to stop generating waves within a preset time period, and the live wire relay 20 is controlled to be in the conducting state, that is, the first relay S1, the second relay S2, and the third relay S3 are engaged.

[0067] Maintain the stop-emission time, i.e., Ts, and calculate the zero-crossing periods ta, tb, and tc of the inverter-side phase voltages Van to Vcn within the preset time. Ts is the preset duration, and the zero-crossing periods of the inverter-side phase voltages Van to Vcn within the preset duration are calculated.

[0068] If the zero-crossing period of a certain inverter-side phase voltage Van to Vcn exceeds the threshold value Tgrid / 2±5%, determine whether the zero-crossing period of the inverter-side phase voltage Van to Vcn is within the time threshold value range of the grid-side phase voltage VAN to VCN, i.e., Tgrid / 2±5%. When the zero-crossing period of the inverter-side phase voltage Van to Vcn is within the time threshold value range of the grid-side phase voltage VAN to VCN, i.e., Tgrid / 2±5%, the first relay S1, the second relay S2, and the third relay S3 will engage normally, indicating that the live wire relay 20 has no open circuit fault and is responding normally to power transmission.

[0069] S1, S2, S3 Abnormal Engagement: When the zero-crossing period of the inverter-side phase voltage Van~Vcn exceeds the time threshold of the grid-side phase voltage VAN~VCN, i.e., Tgrid / 2±5%, the live wire relay 20 is determined to have an open circuit fault.

[0070] The machine will stop and report an error or "relay open circuit".

[0071] Effective value exceeds threshold Vgrid±5%: This determines whether the effective values ​​of the inverter-side phase voltages Van to Vcn exceed the voltage threshold of the grid-side phase voltages VAN to VCN. When the effective values ​​of the inverter-side phase voltages Van to Vcn do not exceed the voltage threshold of the grid-side phase voltages VAN to VCN (Vgrid±5%), the first relay S1, the second relay S2, and the third relay S3 will engage normally, indicating that the live wire relay 20 has no open circuit fault and is transmitting power normally.

[0072] When the effective value of the inverter-side phase voltage Van~Vcn exceeds the voltage threshold of the grid-side phase voltage VAN~VCN, i.e., Vgrid±5%, the live wire relay 20 is determined to have an open circuit fault.

[0073] The machine will stop and report an error or "relay open circuit".

[0074] In summary, this application reserves sufficient downtime at the moment the grid-connected relay engages. During the downtime, the grid clamping is used to detect the zero-crossing state of the inverter-side voltage. Without the need for additional hardware circuitry, it can quickly, accurately, and reliably detect open-circuit faults of the AC relay in both cases where the inverter-side neutral line n and the grid-side neutral line N are shared and not shared.

[0075] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0076] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An open-circuit fault detection circuit, characterized in that, The open-circuit fault detection circuit includes: The system includes an inverter circuit, a live wire relay, and a common control unit. The inverter circuit is connected to the AC power grid in sequence via the inverter-side live wire, the live wire relay, and the grid-side live wire. The inverter circuit is also connected to the AC power grid in sequence via the inverter-side neutral wire, the common control unit, and the grid-side neutral wire. The common control unit is used to control the connection status between the inverter-side neutral wire and the grid-side neutral wire. A driver, connected to the inverter circuit and the live wire relay, is used to control the inverter circuit and the live wire relay according to a drive command; The sampling module is connected to the inverter circuit and the AC grid, and is used to collect the inverter-side phase voltage and the grid-side phase voltage. The controller, connected to the driver and the sampling module, is used to generate different comparison conditions and the driving command based on the inverter-side phase voltage and the grid-side phase voltage, and select the comparison condition according to the connection status to determine whether the live wire relay has an open circuit fault.

2. The open-circuit fault detection circuit according to claim 1, characterized in that, When the open circuit fault detection circuit is powered on, the controller keeps the live wire relay in the open state through the driver. After the inverter side phase voltage exceeds the grid side voltage reference value, the controller controls the inverter circuit to stop generating waves within a preset time period and controls the live wire relay to be in the on state through the driver. During the preset duration, the controller calculates the zero-crossing period and effective value of the inverter-side phase voltage, and the time threshold and voltage threshold of the grid-side phase voltage.

3. The open-circuit fault detection circuit according to claim 2, characterized in that, The comparison conditions include a first condition and a second condition. The first condition is whether the zero-crossing period exceeds the time threshold, and the second condition is whether the effective value of the inverter-side phase voltage exceeds the voltage threshold.

4. The open-circuit fault detection circuit according to claim 3, characterized in that, When the connection status is on, the controller selects the first condition to determine whether the live wire relay has an open circuit fault.

5. The open-circuit fault detection circuit according to claim 4, characterized in that, When the zero-crossing period of the inverter-side phase voltage exceeds the time threshold, the controller determines that the live wire relay corresponding to the inverter-side phase voltage has an open circuit fault. Alternatively, when the zero-crossing period of the inverter-side phase voltage is within the upper or lower limit of the time threshold, the controller determines that the live wire relay corresponding to the inverter-side phase voltage has no open-circuit fault.

6. The open-circuit fault detection circuit according to claim 3, characterized in that, When the connection status is disconnected, the controller selects the second condition to determine whether the fire wire relay has an open circuit fault.

7. The open-circuit fault detection circuit according to claim 6, characterized in that, When the effective value of the inverter-side phase voltage exceeds the voltage threshold, the controller determines that the live wire relay corresponding to the inverter-side phase voltage has an open circuit fault. Alternatively, when the effective value of the inverter-side phase voltage is within the upper or lower limit range of the voltage threshold, the controller determines that the live wire relay corresponding to the inverter-side phase voltage has no open circuit fault.

8. The open-circuit fault detection circuit according to any one of claims 2-7, characterized in that, The grid-side voltage reference value is greater than or equal to the difference between the grid-side phase voltage and the first voltage threshold, and less than or equal to the sum of the grid-side phase voltage and the first voltage threshold; The time threshold of the grid-side phase voltage is greater than or equal to a first percentage of half a grid cycle of the AC grid, and less than or equal to a second percentage of half a grid cycle of the AC grid, wherein the first percentage is less than 1 and the second percentage is greater than 1. The voltage threshold of the grid-side phase voltage is greater than or equal to a third percentage of the effective value of the grid-side phase voltage, and less than or equal to a fourth percentage of the effective value of the grid-side phase voltage, wherein the third percentage is less than 1 and the fourth percentage is greater than 1. The zero-crossing period of the inverter-side phase voltage is obtained based on the preset duration, the grid cycle, and the number of zero-crossings of the grid-side phase voltage.

9. The open-circuit fault detection circuit according to any one of claims 1-7, characterized in that, When the common control unit is a neutral wire relay connected to the driver, the neutral wire relay is used to control the connection state; Alternatively, the shared control unit can be used to control the inverter-side neutral wire to be directly connected to the grid-side neutral wire, or to control the inverter-side neutral wire to be disconnected from the grid-side neutral wire.

10. The open-circuit fault detection circuit according to any one of claims 1-7, characterized in that, The inverter-side live wires include the inverter-side first phase wire, the inverter-side second phase wire, and the inverter-side third phase wire; The grid-side live wire includes a grid-side first phase wire, a grid-side second phase wire, and a grid-side third phase wire; The live wire relay includes at least one relay group connected in series between the inverter-side live wire and the grid-side live wire. Each relay group includes a first relay, a second relay, and a third relay. The first relay is used to control the connection state between the inverter-side first phase wire and the grid-side first phase wire. The second relay is used to control the connection state between the inverter-side second phase wire and the grid-side second phase wire. The third relay is used to control the connection state between the inverter-side third phase wire and the grid-side third phase wire.

11. A method for detecting open-circuit faults, characterized in that, The open circuit fault detection method is applied to an open circuit fault detection circuit, which includes an inverter circuit, a live wire relay, and a common control unit. The inverter circuit is connected to the AC power grid in sequence through the inverter-side live wire, the live wire relay, and the grid-side live wire. The inverter circuit is also connected to the AC power grid in sequence through the inverter-side neutral wire, the common control unit, and the grid-side neutral wire. The common control unit is used to control the connection status between the inverter-side neutral wire and the grid-side neutral wire. The open-circuit fault detection method includes: The drive command controls the inverter circuit and the live wire relay; Collect inverter-side phase voltage and grid-side phase voltage; Different comparison conditions and drive commands are generated based on the inverter-side phase voltage and the grid-side phase voltage, and the comparison conditions are selected according to the connection status to determine whether the live wire relay has an open circuit fault.

12. The open-circuit fault detection method according to claim 11, characterized in that, The open-circuit fault detection method further includes: In response to the power-on of the open-circuit fault detection circuit, the inverter circuit is controlled to generate a wave; When the inverter-side phase voltage exceeds the grid-side voltage reference value, the inverter circuit is controlled to stop transmitting waves within a preset time period, and the live wire relay is controlled to be in the on state. Calculate the zero-crossing period of the inverter-side phase voltage during the preset duration; When the zero-crossing period of the inverter-side phase voltage exceeds the time threshold of the grid-side phase voltage, it is determined that the live wire relay has an open circuit fault. Shut down the machine and report "relay open circuit".

13. The open-circuit fault detection method according to claim 12, characterized in that, The open-circuit fault detection method further includes: When the zero-crossing period of the inverter-side phase voltage is within the time threshold of the grid-side phase voltage, it is determined whether the effective value of the inverter-side phase voltage exceeds the voltage threshold of the grid-side phase voltage. When the effective value of the inverter-side phase voltage exceeds the voltage threshold of the grid-side phase voltage, it is determined that the live wire relay has an open circuit fault. Shut down the machine and report "relay open circuit".

14. The open-circuit fault detection method according to claim 13, characterized in that, The grid-side voltage reference value is greater than or equal to the difference between the grid-side phase voltage and the first voltage threshold, and less than or equal to the sum of the grid-side phase voltage and the first voltage threshold; The time threshold of the grid-side phase voltage is greater than or equal to a first percentage of half a grid cycle of the AC grid, and less than or equal to a second percentage of half a grid cycle of the AC grid, wherein the first percentage is less than 1 and the second percentage is greater than 1. The voltage threshold of the grid-side phase voltage is greater than or equal to a third percentage of the effective value of the grid-side phase voltage, and less than or equal to a fourth percentage of the effective value of the grid-side phase voltage, wherein the third percentage is less than 1 and the fourth percentage is greater than 1. The zero-crossing period of the inverter-side phase voltage is obtained based on the preset duration, the grid cycle of the AC power grid, and the number of zero-crossings of the grid-side phase voltage.

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