Power conversion device and method for detecting leakage current of power conversion device

Abstract

This application provides a power conversion device and a leakage current detection method for the power conversion device, so as to detect abnormalities in the film capacitors in the power conversion device in a timely manner. When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage decreases from the first time point through the second time point, the control unit in the power conversion device outputs a detection result indicating that at least one of the first and second film capacitors has an abnormal leakage current when the absolute value of the current change in each time group within the target detection time is greater than or equal to a first change, and the absolute value of the positive and negative bus voltage changes in each time group is greater than or equal to the target bus voltage change, and / or controls the inverter circuit in the power conversion device to stop working.

Description

Technical Field

[0001] This application relates to the field of capacitor technology, and in particular to a power conversion device and a method for detecting leakage current in the power conversion device. Background Technology

[0002] Film capacitors are capacitors that use polymer films as the dielectric. Due to their advantages of low loss, long lifespan, and self-healing properties, they are widely used in power conversion devices. The self-healing property of film capacitors refers to the phenomenon where, under external conditions, the capacitor repairs itself after dielectric breakdown, restoring it to normal operating conditions. However, if a power conversion device operates for extended periods in harsh environments such as high temperature, high humidity, and high smoke levels, the film capacitors may experience insulation aging over time. Furthermore, the repeated self-healing processes during long-term operation can lead to capacitance decay and mechanical damage, resulting in performance degradation and even short-circuit faults, ultimately causing the power conversion device to malfunction. Therefore, preventing the self-healing of film capacitors from causing malfunctions in power conversion devices is a pressing issue that needs to be addressed. Summary of the Invention

[0003] This application provides a power conversion device and a leakage current detection method for the power conversion device, which can detect abnormalities in the thin film capacitor in a timely manner, avoid the power conversion device from failing to work properly due to the failure of the thin film capacitor, and effectively improve the power generation and stability of the optical power conversion device.

[0004] In a first aspect, this application provides a power conversion device, which may include a control unit, a positive DC bus, a negative DC bus, a first film capacitor, a second film capacitor, and an inverter circuit. The first and second film capacitors are connected in series between the positive and negative DC buses. The inverter circuit is connected between the positive and negative DC buses, and the series connection point of the first and second film capacitors is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. Here, one end of the first film capacitor is connected to the positive DC bus, the other end of the first film capacitor is connected to one end of the second film capacitor, and the other end of the second film capacitor is connected to the negative DC bus. The series connection point between the first and second film capacitors is the connection point between the two film capacitors. The series connection point between the first and second film capacitors can be the midpoint of the bus (referred to as the midpoint).

[0005] In at least one time group, if the positive bus voltage decreases from the first time point through the second time point and the negative bus voltage increases from the first time point through the second time point, or if the positive bus voltage increases from the first time point through the second time point and the negative bus voltage decreases from the first time point through the second time point, the control unit may output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors when the absolute value of the change in current flowing through the series connection terminal of the first and second film capacitors between the first and second time points in each time group within the target detection time is greater than or equal to a first change, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group is greater than or equal to the target bus voltage change. This will allow the control unit to output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors, and / or control the inverter circuit to stop operating. The time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0006] In this embodiment, leakage current may exist at the breakdown point of the film capacitor due to factors such as imperfect dielectric or manufacturing defects. The higher the leakage current, the greater the current density at the breakdown point, leading to a rapid increase in temperature. Excessive temperature causes the dielectric to evaporate or melt rapidly. The evaporated or melted portion of the dielectric forms an insulating layer, separating the breakdown point and thus achieving self-healing of the film capacitor. However, during this self-healing process, excessive leakage current may affect the performance of the film capacitor, leading to its failure. When neither the first nor the second film capacitor exhibits abnormal leakage current, the midpoint potential is balanced. At this time, the positive bus voltage and the negative bus voltage are equal, and the current change and the changes in both the positive and negative bus voltages remain unchanged. When the first film capacitor exhibits abnormal leakage current, the trends in the positive and negative bus voltages are as follows: the positive bus voltage decreases compared to when there is no abnormal leakage current, and the negative bus voltage increases compared to when there is no abnormal leakage current; both the current change and the changes in both the positive and negative bus voltages change. When the second film capacitor exhibits an abnormal leakage current, the trends of the positive and negative bus voltages are as follows: the positive bus voltage increases compared to when there is no abnormal leakage current, while the negative bus voltage decreases. Changes in both current and the magnitudes of these changes also occur. Therefore, the trends of the positive and negative bus voltages, along with the changes in both voltage and current, can reflect the real-time changes in the positive and negative bus voltages and the midpoint current. This allows for the detection of whether the first or second film capacitor has an abnormal leakage current, offering advantages such as high accuracy, high efficiency, and low cost.

[0007] In one possible implementation, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit can output a detection result indicating abnormal leakage current in the first film capacitor when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the changes in the positive and negative bus voltages corresponding to each time group is greater than or equal to the target bus voltage change. It is understood that when the first film capacitor exhibits abnormal leakage current, the positive bus voltage decreases compared to when the first film capacitor does not exhibit abnormal leakage current, and the negative bus voltage increases compared to when the first film capacitor does not exhibit abnormal leakage current; both the current change and the changes in the positive and negative bus voltages change. Therefore, the changing trends of the positive and negative bus voltages, as well as the current change and the changes in the positive and negative bus voltages, can reflect the leakage current status of the film capacitor in real time. Therefore, when the positive and negative bus voltages in each time group meet the above-mentioned trend, based on the absolute value of the current change and the absolute value of the positive and negative bus voltage changes in each time group, it is possible to detect the presence of abnormal leakage current in a timely and rapid manner. It is also possible to locate the film capacitor with abnormal leakage current, making it convenient for technicians to replace the film capacitor.

[0008] In one possible implementation, when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating that the second thin-film capacitor has an abnormal leakage current when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change.

[0009] Understandably, when the second film capacitor exhibits abnormal leakage current, the positive bus voltage increases compared to when the first film capacitor does not have abnormal leakage current, while the negative bus voltage decreases. Both the current change and the changes in both positive and negative bus voltages also change. Therefore, the trends in the positive and negative bus voltages, as well as the changes in current and voltage, can reflect the leakage current status of the film capacitors in real time. Thus, when the positive and negative bus voltages in each time group meet the aforementioned trends, the absolute values ​​of the current and voltage changes in each time group can be used to detect abnormal leakage currents quickly and promptly. Furthermore, the film capacitor with the abnormal leakage current can be located, facilitating replacement by technicians.

[0010] In one possible implementation, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current when the absolute value of the current change corresponding to each time group in the target detection time is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, and / or control the inverter circuit to stop working.

[0011] It is understandable that the current changes and positive and negative bus voltage changes corresponding to each time group may abruptly change, causing the absolute value of the current change in each time group to be greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes in each time group to be greater than or equal to the target bus voltage change. Therefore, it is possible to detect whether the absolute value of the current change in each time group within the target detection time is consistently greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes in each time group is consistently greater than or equal to the target bus voltage change. When the positive and negative bus voltages in each time group meet the trend of abnormal leakage current in the first or second film capacitor, if the absolute value of the current change in each time group within the target detection time is greater than or equal to the first change and the absolute value of the positive and negative bus voltage changes in each time group is greater than or equal to the target bus voltage change, it can be determined whether the first or second film capacitor has an abnormal leakage current. This allows for timely and rapid detection of abnormal leakage current and pinpointing the film capacitor with the abnormal leakage current, improving the accuracy of abnormal leakage current detection.

[0012] In one possible implementation, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit may output a detection result indicating that the first thin-film capacitor has an abnormal leakage current when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

[0013] It is understandable that by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage change corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detection caused by abrupt changes in the current change and the positive and negative bus voltage change corresponding to each time group can be avoided, thus effectively improving detection accuracy.

[0014] In one possible implementation, when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating abnormal leakage current in the second thin-film capacitor when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

[0015] It is understandable that by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage change corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detection caused by abrupt changes in the current change and the positive and negative bus voltage change corresponding to each time group can be avoided, thus effectively improving detection accuracy.

[0016] In one possible implementation, the inverter circuit is connected to the DC input unit via a DC disconnectable switch and to the power grid via a grid-connected relay. During the inverter circuit's shutdown process, the control unit can control the DC disconnectable switch and the grid-connected relay to disconnect when the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to a preset voltage change, thereby disconnecting the inverter circuit from the DC input unit and the power grid. The preset voltage change is greater than the target bus voltage change.

[0017] Understandably, theoretically, when the inverter circuit stops operating, the voltages of the first and second thin-film capacitors should no longer change, meaning the positive and negative bus voltages should remain constant. However, if, when the inverter circuit stops operating, the absolute value of the voltage change of the positive and negative buses corresponding to at least one time group is still detected to be higher than or equal to a preset voltage change, it can be determined that either the first or second thin-film capacitor still has an abnormal leakage current. In this case, due to the uneven voltage distribution between the first and second thin-film capacitors, one of the capacitors may be damaged due to excessive voltage, potentially leading to a malfunction of the power conversion device. Furthermore, the inverter circuit can be disconnected from the DC input unit and the power grid to prevent the fault from spreading and to avoid damage to other components.

[0018] In one possible implementation, the control unit can control the inverter circuit to operate in derating mode when the number of abnormal leakage currents of the film capacitors in the power converter reaches a target number within a preset detection time, thereby reducing the output power of the inverter circuit. It is understood that the power converter may operate under harsh conditions such as high temperature and high humidity for extended periods. The long-term self-healing accumulation of the film capacitors may accelerate their aging and cause capacitance decay, leading to a decline in their performance. Therefore, the performance status of the film capacitors can be predicted by the number of abnormal leakage currents. When the number of abnormal leakage currents reaches the target number, the inverter circuit can be controlled to operate in derating mode to prevent the film capacitors from burning out due to excessive leakage current. This can, to some extent, slow down the aging rate of the film capacitors and prevent power converter malfunctions caused by film capacitor failure.

[0019] In one possible implementation, the control unit can stop the power conversion device when the total number of abnormal leakage currents detected in the film capacitors reaches a preset number. Specifically, when the total number of abnormal leakage currents in the first and second film capacitors exceeds the preset number, it can be predicted that the safety performance of the first and second film capacitors is low. Therefore, the power conversion device can be stopped in advance to prevent film capacitor failure. It is understood that when the number of abnormal leakage currents in the film capacitors reaches the limit value, the safety performance of the film capacitors is low, which may lead to film capacitor failure, resulting in the film capacitors burning out and potentially damaging other electronic components, causing the fault to spread. To avoid the above-mentioned failure situations, the power conversion device can be stopped in advance when the total number of abnormal leakage currents in the film capacitors reaches the preset number, preventing damage to other electronic components and ensuring the safety of the power conversion device and the photovoltaic power generation system.

[0020] Secondly, this application also provides a power conversion device, which may include a control unit, a positive DC bus, a negative DC bus, a first film capacitor, a second film capacitor, and an inverter circuit. The first and second film capacitors are connected in series between the positive and negative DC buses. The inverter circuit is connected between the positive and negative DC buses, and the series connection point of the first and second film capacitors is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. Here, one end of the first film capacitor is connected to the positive DC bus, the other end of the first film capacitor is connected to one end of the second film capacitor, and the other end of the second film capacitor is connected to the negative DC bus. The series connection point between the first and second film capacitors is the connection point between the two film capacitors. The series connection point between the first and second film capacitors can be the midpoint of the bus.

[0021] In at least one time group, if the positive bus voltage decreases from the first time point through the second time point and the negative bus voltage increases from the first time point through the second time point, or if the positive bus voltage increases from the first time point through the second time point and the negative bus voltage decreases from the first time point through the second time point, the control unit can process the change in current flowing through the series connection of the first and second film capacitors between the first and second time points in each time group within the target detection time to obtain the change in current within the target detection time. If the absolute value of the change in current within the target detection time is greater than or equal to a second change, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group is greater than or equal to the change in target bus voltage, the control unit outputs a detection result indicating abnormal leakage current in at least one of the first and second film capacitors, and / or controls the inverter circuit to stop operating. The time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0022] Understandably, the positive and negative bus voltages exhibit different trends when the first or second film capacitor has an abnormal leakage current compared to when it does not, resulting in changes in both current and voltage. Therefore, if the trends of the positive and negative bus voltages match those of the first or second film capacitor with an abnormal leakage current, the presence of an abnormal leakage current in the film capacitor can be determined based on these trends, the current change within the target detection time, and the corresponding changes in positive and negative bus voltages for each time group. This allows for timely and rapid detection of the abnormal leakage current and pinpointing the affected film capacitor. Furthermore, processing the current change rate for each time group to obtain the current change within the target detection time avoids inaccurate detection due to outliers or missing values, thus improving the accuracy of detecting abnormal leakage current.

[0023] In one possible implementation, the control unit can integrate the current changes corresponding to each time group within the target detection time to obtain the current change within the target detection time. Here, since the first time point in each time group can be a continuous time point, and the second time point in each time group can also be a continuous time point, the time groups themselves can also be continuous, and the current changes corresponding to each time group can also be continuous. Therefore, the current changes corresponding to each time group within the target detection time can be integrated to obtain the current change within the target detection time. It is understood that leakage current anomaly detection can be performed based on the positive and negative bus voltage changes corresponding to each time group and the current change within the target detection time obtained after integration. Furthermore, by integrating the current changes corresponding to each time group, the data processing accuracy can be further improved. The integrated current changes and positive and negative bus voltage changes can more accurately reflect the self-healing status of the thin-film capacitor, thereby improving the accuracy of leakage current anomaly detection.

[0024] In one possible implementation, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit can output a detection result indicating abnormal leakage current in the first thin-film capacitor when the absolute value of the change within the target detection time is greater than or equal to a second change, and the absolute value of the changes in the positive and negative bus voltages corresponding to each time group is greater than or equal to the target bus voltage change. Here, the second change can be the product of the first change and the target detection time.

[0025] Understandably, by integrating the current changes corresponding to each time group, the problem of inaccurate detection due to outliers or missing values ​​can be avoided, and the accuracy of data processing can be further improved. In turn, based on the current changes within the target detection time and the positive and negative bus voltage changes corresponding to each time group, the self-healing status of the thin film capacitor can be reflected more accurately, thereby improving the accuracy of detecting leakage current anomalies.

[0026] In one possible implementation, when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, the control unit is further configured to output a detection result indicating abnormal leakage current in the second thin-film capacitor when the absolute value of the change within the target detection time is greater than or equal to a second change, and the absolute values ​​of the changes in the positive and negative bus voltages corresponding to each time group are greater than or equal to the target bus voltage change. Here, the second change can be the product of the first change and the target detection time.

[0027] Understandably, by integrating the current changes corresponding to each time group, the problem of inaccurate detection due to outliers or missing values ​​can be avoided, and the data processing accuracy can be further improved. In turn, based on the current changes within the target detection time and the positive and negative bus voltage changes corresponding to each time group, the self-healing status of the thin film capacitor can be reflected more accurately, thereby improving the accuracy of detecting leakage current anomalies.

[0028] Thirdly, this application also provides a leakage current detection method for a power conversion device. The power conversion device may include a control unit, a positive DC bus, a negative DC bus, a first film capacitor, a second film capacitor, and an inverter circuit. The first and second film capacitors are connected in series between the positive and negative DC buses. The inverter circuit is connected between the positive and negative DC buses, and the series connection terminal of the first and second film capacitors is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. Here, one end of the first film capacitor is connected to the positive DC bus, the other end of the first film capacitor is connected to one end of the second film capacitor, and the other end of the second film capacitor is connected to the negative DC bus. The series connection terminal of the first and second film capacitors is the connection point between the two film capacitors. The series connection terminal of the first and second film capacitors can be the midpoint of the bus. The method includes:

[0029] The absolute value of the change in current flowing through the series connection of the first and second film capacitors between the first and second time points in each time group in at least one time group is obtained, as well as the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group in at least one time group; the time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0030] When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the system outputs a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or controls the inverter circuit to stop working.

[0031] Understandably, when the first film capacitor exhibits abnormal leakage current, the positive bus voltage decreases compared to when it does not, while the negative bus voltage increases. Both the current change and the changes in both the positive and negative bus voltages also change. Similarly, when the second film capacitor exhibits abnormal leakage current, the positive bus voltage increases compared to when it does not, while the negative bus voltage decreases. Both the current change and the changes in both the positive and negative bus voltages also change. Therefore, the trends in the positive and negative bus voltages, as well as the changes in the current and the changes in both the positive and negative bus voltages, can reflect the leakage current status of the film capacitors in real time. This allows for timely and rapid detection of abnormal leakage currents and can also pinpoint the film capacitor with the abnormal leakage current, facilitating replacement by technicians.

[0032] In one possible implementation, the detection result of leakage current anomaly in at least one of the first and second film capacitors is output, including: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the detection result of leakage current anomaly in the first film capacitor is output when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change. It is understood that when leakage current anomaly exists in the first film capacitor, the positive bus voltage decreases compared to when there is no leakage current anomaly, and the negative bus voltage increases compared to when there is no leakage current anomaly; both the current change and the changes in the positive and negative bus voltages change. Therefore, when the positive and negative bus voltages of each time group satisfy the above-mentioned changing trend, the presence of leakage current anomaly in the first film capacitor can be determined based on the absolute value of the current change and the absolute value of the positive and negative bus voltage changes corresponding to each time group.

[0033] In one possible implementation, the detection result of leakage current anomaly in at least one of the first and second film capacitors is output, including: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the detection result of leakage current anomaly in the second film capacitor is output. It is understood that when leakage current anomaly exists in the second film capacitor, the positive bus voltage increases compared to when there is no leakage current anomaly, and the negative bus voltage decreases compared to when there is no leakage current anomaly; both the current change and the changes in the positive and negative bus voltages change. It is evident that the changing trends of the positive and negative bus voltages, the changes in current, and the changes in both positive and negative bus voltages can reflect the leakage current status of the film capacitor in real time. This allows for timely and rapid detection of any abnormal leakage current, and also enables the location of the film capacitor with the abnormal leakage current, facilitating the replacement of the film capacitor by technicians.

[0034] In one possible implementation, the method further includes: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point; or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, when the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, outputting a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or controlling the inverter circuit to stop working.

[0035] It is understandable that the current changes and positive and negative bus voltage changes corresponding to each time group may abruptly change, causing the absolute value of the current change in each time group to be greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes in each time group to be greater than or equal to the target bus voltage change. Therefore, it is possible to detect whether the absolute value of the current change in each time group within the target detection time is consistently greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes in each time group is consistently greater than or equal to the target bus voltage change. When the positive and negative bus voltages in each time group meet the trend of abnormal leakage current in the first or second film capacitor, if the absolute value of the current change in each time group within the target detection time is greater than or equal to the first change and the absolute value of the positive and negative bus voltage changes in each time group is greater than or equal to the target bus voltage change, it can be determined whether the first or second film capacitor has an abnormal leakage current. This allows for timely and rapid detection of abnormal leakage current and pinpointing the film capacitor with the abnormal leakage current, improving the accuracy of abnormal leakage current detection.

[0036] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second thin-film capacitors is provided, including: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of abnormal leakage current in the first thin-film capacitor is provided. It is understood that by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0037] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second thin-film capacitors is provided, including: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of abnormal leakage current in the second thin-film capacitor is provided. It is understood that by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0038] In one possible implementation, the inverter circuit is connected to the DC input unit via a DC disconnectable switch, and the inverter circuit is connected to the power grid via a grid-connected relay. The method further includes: during the process of the inverter circuit stopping operation, when the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to a preset voltage change, controlling the DC disconnectable switch and the grid-connected relay to disconnect the inverter circuit from the DC input unit and the power grid; the preset voltage change is greater than the target bus voltage change.

[0039] Understandably, if, during the process of the inverter circuit stopping operation, the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to the preset voltage change, the inverter circuit can be controlled to disconnect from the DC input unit and the power grid to avoid damage to the first or second film capacitor due to overvoltage, thereby reducing the possibility of power conversion device failure.

[0040] In one possible implementation, the method further includes: when the number of times the leakage current abnormality of the thin-film capacitor in the power conversion device is detected within a preset detection time reaches a target abnormality number, controlling the inverter circuit to operate in derating mode to reduce the output power of the inverter circuit. It is understood that when the power conversion device operates under harsh conditions such as high temperature and high humidity for a long time, the long-term self-healing accumulation of the thin-film capacitor may accelerate its aging and may also cause its capacitance to decay, leading to a decline in its performance. Therefore, the performance status of the thin-film capacitor can be predicted by the number of leakage current abnormalities. When the number of leakage current abnormalities reaches the target abnormality number, the inverter circuit can be controlled to operate in derating mode to avoid burning out the thin-film capacitor due to excessive leakage current. This can, to a certain extent, slow down the aging rate of the thin-film capacitor and prevent power conversion device failure caused by thin-film capacitor failure.

[0041] In one possible implementation, the method further includes: controlling the power conversion device to stop operating when the total number of abnormal leakage currents detected in the photovoltaic power generation system reaches a preset number of abnormalities. It is understood that when the number of abnormal leakage currents in the film capacitor reaches its limit, the safety performance of the film capacitor is low, which may lead to its failure, resulting in burnout and potential damage to other electronic components, causing the fault to spread. To avoid these failures, the power conversion device can be controlled to stop operating in advance when the total number of abnormal leakage currents in the film capacitor reaches the preset number of abnormalities, preventing damage to other electronic components and ensuring the safety of both the power conversion device and the photovoltaic power generation system.

[0042] Fourthly, this application also provides a leakage current detection method for a power conversion device. The power conversion device may include a control unit, a positive DC bus, a negative DC bus, a first film capacitor, a second film capacitor, and an inverter circuit. The first and second film capacitors are connected in series between the positive and negative DC buses. The inverter circuit is connected between the positive and negative DC buses, and the series connection terminal of the first and second film capacitors is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. Here, one end of the first film capacitor is connected to the positive DC bus, the other end of the first film capacitor is connected to one end of the second film capacitor, and the other end of the second film capacitor is connected to the negative DC bus. The series connection terminal of the first and second film capacitors is the connection point between the two film capacitors. The series connection terminal of the first and second film capacitors can be the midpoint of the bus. The method includes:

[0043] The method acquires the change in current flowing through the series connection of the first and second film capacitors between the first and second time points in each time group within at least one time group, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group within at least one time group. The method then processes the current change corresponding to each time group within the target detection time to obtain the current change within the target detection time. The time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0044] When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the system outputs a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or controls the inverter circuit to stop working.

[0045] Understandably, the positive and negative bus voltages exhibit different trends when the first or second film capacitor has an abnormal leakage current compared to when it does not, resulting in changes in both the current change and the changes in both the positive and negative bus voltages. Furthermore, by processing the current change rate corresponding to each time group to obtain the current change within the target detection time, the problem of inaccurate detection due to outliers or missing values ​​can be avoided, improving the accuracy of detecting abnormal leakage current. This also allows for timely and rapid detection of the presence of abnormal leakage current and the location of the film capacitor exhibiting the abnormal leakage current.

[0046] In one possible implementation, the above-mentioned processing based on the current change corresponding to each time group within the target detection time to obtain the current change within the target detection time includes: integrating the current change corresponding to each time group within the target detection time to obtain the current change within the target detection time. Here, since the first time point in each time group can be a continuous time point, and the second time point in each time group can also be a continuous time point, then each time group can also be a continuous time group, and the current change corresponding to each time group can also be continuous. Therefore, the current change corresponding to each time group within the target detection time can be integrated to obtain the current change within the target detection time. It is understood that performing leakage current anomaly detection based on the positive and negative bus voltage changes corresponding to each time group and the current change within the target detection time obtained after integration processing can further improve the data processing accuracy. Based on the current change after integration processing and the positive and negative bus voltage changes, the self-healing status of the thin film capacitor can be more accurately reflected, thereby improving the accuracy of leakage current anomaly detection.

[0047] In one possible implementation, the detection result of abnormal leakage current of at least one of the first and second film capacitors is output as follows: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, when the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of abnormal leakage current of the first film capacitor is output.

[0048] Understandably, detecting leakage current anomalies in the first thin-film capacitor based on the changes in positive and negative bus voltages corresponding to each time group and the changes in current within the target detection time can further improve the accuracy of data processing. The changes in current and positive and negative bus voltages after integration can more accurately reflect the self-healing status of the thin-film capacitor, thereby improving the accuracy of detecting leakage current anomalies.

[0049] In one possible implementation, the detection result of abnormal leakage current of at least one of the first and second film capacitors is output as follows: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of abnormal leakage current of the second film capacitor is output.

[0050] Understandably, by integrating the current changes corresponding to each time group, the accuracy of data processing can be further improved. Based on the current changes and positive and negative bus voltage changes after integration, the self-healing status of the thin film capacitor can be reflected more accurately, thereby improving the accuracy of detecting leakage current anomalies. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of a photovoltaic power generation system provided in an embodiment of this application;

[0052] Figure 2 This is another structural schematic diagram of the photovoltaic power generation system provided in the embodiments of this application;

[0053] Figure 3 This is a schematic diagram of current parameter variation provided in an embodiment of this application;

[0054] Figure 4 This is another schematic diagram of current parameter changes provided in an embodiment of this application;

[0055] Figure 5 This is another structural schematic diagram of the photovoltaic power generation system provided in the embodiments of this application;

[0056] Figure 6 A flowchart illustrating a leakage current detection method for a power conversion device provided in an embodiment of this application;

[0057] Figure 7 This is another schematic flowchart of the leakage current detection method for the power conversion device provided in the embodiments of this application. Detailed Implementation

[0058] Power conversion devices, capable of converting electrical energy from one form to another (e.g., alternating current to direct current, or vice versa), are widely used in renewable energy, electric vehicles, and industrial fields, particularly in photovoltaic (PV) power generation. Solar PV power generation, with its characteristics of no moving parts, no noise, no pollution, and high reliability, has excellent application prospects in remote areas. PV systems can be used to power various types of electrical equipment, such as base station equipment, batteries, or household appliances (e.g., refrigerators, air conditioners), depending on the specific application scenario. The power conversion device provided in this application is suitable for the aforementioned PV systems. It can convert the variable DC voltage generated by DC power sources such as photovoltaic solar panels into AC power at the mains frequency and output this AC power to the mains grid for use. Specifically, it can be used by base station equipment, batteries, or household appliances within the mains grid. The power conversion device provided in this application is adaptable to different application scenarios and is not limited thereto.

[0059] See Figure 1 , Figure 1 This is a structural schematic diagram of a photovoltaic power generation system provided in an embodiment of this application. For example... Figure 1 As shown, a photovoltaic power generation system may include a DC input unit and a power conversion device. The power conversion device may include a positive DC bus BUS+, a negative DC bus BUS-, a capacitor unit, and an inverter circuit. The first output terminal of the DC input unit is connected to the positive DC bus BUS+, and the second output terminal is connected to the negative DC bus BUS-. The capacitor unit is connected between the positive and negative DC buses BUS+ and BUS- respectively. The first connection terminal of the capacitor unit is connected to the positive DC bus BUS+, the second connection terminal is connected to the negative DC bus BUS-, and the third connection terminal is connected to the inverter circuit. The output terminal of the inverter circuit is used to connect to the power grid. The inverter circuit can convert the DC power provided by the DC input unit into AC power and output it to the power grid or load. The capacitor unit includes at least one thin-film capacitor. The DC power provided by the DC input unit is transmitted to the capacitor unit through the positive and negative DC buses (BUS+, BUS-) and stored in the capacitor unit.

[0060] In some feasible implementations, the DC input unit may include a photovoltaic string and a DC-DC converter circuit. The output terminal of the photovoltaic string can be connected to the input terminal of the DC-DC converter circuit, the positive output terminal of the DC-DC converter circuit can be connected to the positive DC bus BUS+, and the negative output terminal of the DC-DC converter circuit can be connected to the negative DC bus BUS-. The DC-DC converter circuit can perform voltage conversion (e.g., boost) on the DC power from the photovoltaic string and output the voltage-converted DC power to the inverter circuit. The inverter circuit sequentially inverts the input DC power to obtain AC power that meets the requirements of the power grid or load, thereby enabling power supply to various types of electrical equipment, including those connected to the AC power grid. Optionally, the DC input unit may also include an energy storage battery, which can be connected to the DC-DC converter circuit. The DC-DC converter circuit can perform voltage conversion on the DC power from the energy storage battery and output the voltage-converted DC power to the inverter circuit. Here, the DC-DC converter circuit and the inverter circuit connected to the energy storage battery can be a bidirectional DC-DC converter circuit and a bidirectional inverter circuit, thereby achieving the function of converting DC power to AC power and vice versa. Optionally, the DC input unit may also include a DC power supply to output DC power to the DC-DC converter circuit. It should be understood that the DC input unit can be determined based on the actual application scenario and is not limited thereto. The inverter circuit sequentially inverts the DC power input from the capacitor unit to obtain AC power that meets the requirements of the power grid or load, thereby enabling the supply of power to various types of electrical equipment, including those connected to the AC power grid.

[0061] It should be noted that when a DC voltage is applied to a film capacitor, factors such as imperfections in the dielectric or manufacturing defects, such as a breakdown point in the dielectric, may cause a small current leakage, which can be called leakage current. Since the leakage current is concentrated in a very small area, the higher the leakage current value, the greater the current density in that area, leading to a rapid rise in temperature. Excessive temperature causes the dielectric to evaporate or melt rapidly. The evaporated or melted portion of the dielectric will re-condense due to the sudden drop in temperature in the discharge area, forming an insulating layer that separates the breakdown point, thus preventing a short circuit and restoring the insulation of the film capacitor so it can continue to operate normally. This is called the self-healing process of the film capacitor. However, during this self-healing process, excessive leakage current may affect the performance of the film capacitor, especially in high-precision circuits (such as filter circuits, power circuits, timing circuits, etc.), potentially causing voltage drop, energy loss, or even circuit failure. Secondly, excessive leakage current can also cause the film capacitor to overheat, accelerating its aging and leading to its failure. This can even damage other electronic components, causing the fault to spread and reducing the stability of the photovoltaic power generation system. Ultimately, this can result in system shutdown or damage, causing irreparable economic losses. Figure 1The photovoltaic power generation system shown typically operates in harsh environments such as high temperature, high humidity, and high smoke. Prolonged exposure to these conditions can accelerate the insulation aging of thin-film capacitors. When an aging thin-film capacitor undergoes self-healing, its leakage current is higher than that of a capacitor without insulation aging, and the capacitance decay is also more severe. This can lead to a decrease in the capacitor voltage, causing the photovoltaic system to shut down due to overcurrent or undervoltage, thereby reducing the system's stability and power generation efficiency. Furthermore, if a short-circuit fault occurs in the thin-film capacitor due to repeated self-healing, the DC current in the DC input unit may bypass the thin-film capacitor and flow directly into the positive and negative DC buses BUS-, leading to a short circuit and fault propagation. Therefore, timely detection of abnormal leakage current in thin-film capacitors and prevention of low photovoltaic system efficiency due to long-term self-healing are technical problems that urgently need to be solved by those skilled in the art.

[0062] Therefore, this application provides a photovoltaic power generation system that can detect in a timely manner whether there is abnormal leakage current in the thin film capacitor, and can also avoid the problem of low working efficiency of the photovoltaic system due to long-term self-healing of the thin film capacitor, thus ensuring the safe and stable operation of the photovoltaic power generation system, with high reliability and strong applicability.

[0063] The above are merely examples of application scenarios for the power conversion device provided in this application, and are not exhaustive. This application does not limit the application scenarios.

[0064] The specific implementation principle of the photovoltaic power generation system provided in the embodiments of this application will be described below with reference to the accompanying drawings.

[0065] For example, see Figure 2 , Figure 2This is another structural schematic diagram of the photovoltaic power generation system provided in this application embodiment. The photovoltaic power generation system may include a DC input unit and a power conversion device. The power conversion device may include a control unit, a positive DC bus BUS+, a negative DC bus BUS-, a first thin-film capacitor C1, a second thin-film capacitor C2, and an inverter circuit. The DC terminal of the photovoltaic power generation system may include a first output terminal dc1 and a second output terminal dc2 of the DC input unit. The first output terminal dc1 is connected to the positive DC bus BUS+, and the second output terminal dc2 is connected to the negative DC bus BUS-. The first thin-film capacitor C1 and the second thin-film capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The inverter circuit is connected between the positive DC bus BUS+ and the negative DC bus BUS-, and the series connection terminal of the first thin-film capacitor C1 and the second thin-film capacitor C2 is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. The inverter circuit converts the DC power supplied by the DC input unit into AC power, which is then output to the power grid or load. Here, one end of the first film capacitor C1 is connected to the positive DC bus BUS+, and the other end is connected to one end of the second film capacitor C2. The other end of the second film capacitor C2 is connected to the negative DC bus BUS-. The series connection point N between the first film capacitor C1 and the second film capacitor C2 is the connection point between the two film capacitors. This series connection point N can be the midpoint of the bus (referred to as the midpoint). The DC power supplied by the DC input unit can be transmitted to the first film capacitor C1 and the second film capacitor C2 through the positive and negative DC buses (BUS+, BUS-), and stored as energy by the first and second film capacitors C1 and C2. The first and second film capacitors C1 and C2 can also be used for midpoint balancing control to ensure that the capacitor voltage of the first film capacitor C1 is equal to the capacitor voltage of the second film capacitor C2.

[0066] like Figure 2 As shown, the current flowing through the first film capacitor C1 can be denoted as Ic1, and the current flowing through the second film capacitor C2 can be denoted as Ic2. The capacitor voltage of the first film capacitor C1 is equal to the positive bus voltage (i.e., the voltage of the positive DC bus BUS+ to the midpoint N), which can be denoted as Uc1. The capacitor voltage of the second film capacitor C2 is equal to the negative bus voltage (i.e., the voltage of the negative DC bus BUS- to the midpoint N), which can be denoted as Uc2. The midpoint current flowing through the midpoint N (hereinafter referred to as the midpoint current) can be denoted as io. When the direction of the midpoint current is from the midpoint N to the inverter circuit, the direction of the current in the first film capacitor C1 is from the positive DC bus BUS+ to the midpoint N, and the direction of the current in the second film capacitor C2 is from the midpoint N to the negative DC bus BUS-. The currents of the first film capacitor C1 and the second film capacitor C2 at this time can be found in the following formulas:

[0067]

[0068] Where Cf1 can be the capacitance of the first film capacitor C1, Cf2 can be the capacitance of the second film capacitor C2, and Uo can be the midpoint potential. Ideally, if C1 = C2 = C and Uc1 = Uc2, the first film capacitor C1 and the second film capacitor C2 balance the DC-side voltage. In this case, according to Kirchhoff's Law (KCL), we have:

[0069]

[0070] Where io can be the midpoint current, and U o It can be the midpoint potential. It can be the rate of change of the midpoint potential.

[0071] From formulas (3) and (4), it can be seen that the magnitude of the midpoint current is proportional to the rate of change of the midpoint potential. When the midpoint potential is balanced, the midpoint potential is the reference zero potential, and the midpoint current is the reference zero current, i.e., Uo = 0, io = 0. When the midpoint potential is unbalanced, the midpoint potential shifts, the midpoint potential is not 0, and the midpoint current is not 0. That is, the capacitor voltage of the first film capacitor C1 is not equal to the capacitor voltage of the second film capacitor C2 (i.e., the positive bus voltage is not equal to the negative bus voltage), and the current flowing into the midpoint N is not equal to the current flowing out of the midpoint N. Furthermore, since the self-healing of the film capacitor is due to the evaporation or melting of the dielectric near the breakdown point caused by the increase of leakage current, an insulating layer is formed. Therefore, in cases such as Figure 2 In the photovoltaic power generation system shown, when the leakage current of the first thin-film capacitor C1 or the second thin-film capacitor C2 is too high, the capacitance of the capacitor may decrease, and its voltage may drop, leading to unequal voltages on the positive and negative bus lines. This causes an imbalance in the midpoint potential, resulting in a shift in the midpoint potential and a change in the midpoint current. In summary, when the leakage current of the first thin-film capacitor C1 or the second thin-film capacitor C2 is too high, both the positive and negative bus line voltages and the midpoint current will change. Therefore, the presence of abnormal leakage current in the thin-film capacitors can be determined based on the midpoint current and the positive and negative bus line voltages. The abnormality caused by excessive leakage current during the self-healing process of the thin-film capacitor can be termed a leakage current anomaly.

[0072] For example, taking the abnormal leakage current of the first thin-film capacitor C1 as an example, please refer to... Figure 3 , Figure 3 This is a schematic diagram of current parameter changes provided in an embodiment of this application. Figure 3As shown, when neither the first film capacitor C1 nor the second film capacitor C2 exhibits abnormal leakage current, such as at time t1, the midpoint potential is balanced, the positive bus voltage and the negative bus voltage are equal, and the voltage fluctuation amplitudes of the positive and negative bus voltages are also equal. The leakage current and midpoint current of the first film capacitor C1 remain essentially unchanged. At time t2, the first film capacitor C1 breaks down, and leakage current exists at the breakdown point. When the leakage current is too high, the current flowing through the first film capacitor C1 increases due to the leakage current, and the capacitor voltage of the first film capacitor C1 decreases due to the capacitance decay, causing the capacitor voltage of the second film capacitor C2 to increase. In other words, the midpoint potential is unbalanced due to the abnormal leakage current of the first film capacitor C1. At this time, compared to time t1, the positive bus voltage decreases and the negative bus voltage increases at time t2. To balance the midpoint potential, the positive bus voltage and the negative bus voltage can be equalized again through midpoint balance control. The midpoint balance control method should be familiar to those skilled in the art and will not be elaborated upon here. Specifically, due to the abnormal leakage current of the first thin-film capacitor C1, the positive bus voltage can be gradually increased and the negative bus voltage can be gradually decreased to achieve midpoint balance. At this time, the midpoint potential gradually decreases. For example, at time t3, according to formula (4), the midpoint current increases due to the decrease in midpoint potential. At time t4, the positive bus voltage increases due to midpoint balance control, and the negative bus voltage decreases due to midpoint balance control, until the positive bus voltage and the negative bus voltage are equal again.

[0073] Please see Figure 4 , Figure 4 This is another schematic diagram of current parameter changes provided in an embodiment of this application. For example... Figure 4As shown, when neither the first film capacitor C1 nor the second film capacitor C2 exhibits abnormal leakage current, such as at time t1', the midpoint potential is balanced, the positive bus voltage and the negative bus voltage are equal, and the voltage fluctuation amplitudes of the positive and negative bus voltages are also equal. The leakage current and midpoint current of the first film capacitor C1 remain essentially unchanged. At time t2', the second film capacitor C2 breaks down, and leakage current exists in it. The current flowing through the first film capacitor C1 increases due to the leakage current, and the capacitor voltage of the second film capacitor C2 decreases due to its capacitance decay, causing the capacitor voltage of the first film capacitor to increase. In other words, the midpoint potential becomes unbalanced due to the abnormal leakage current in the second film capacitor C2. At this time, compared to time t1', the positive bus voltage increases and the negative bus voltage decreases at time t2'. To balance the midpoint potential, midpoint balance control can be used to make the positive and negative bus voltages equal again. Specifically, due to the abnormal leakage current of the second thin-film capacitor C2, the positive bus voltage can be gradually decreased and the negative bus voltage gradually increased to achieve midpoint balance. During this process, the midpoint potential gradually increases. For example, at time t3', the midpoint current decreases due to the increased midpoint potential. At time t4', the positive bus voltage decreases due to midpoint balance control, and the negative bus voltage increases due to midpoint balance control, until the positive and negative bus voltages are equal again.

[0074] In summary, when any thin-film capacitor experiences leakage current anomaly, its voltage decreases, and the current flowing through it increases. In a photovoltaic power generation system, since the first thin-film capacitor C1 and the second thin-film capacitor C2 represent the positive and negative bus voltages, respectively, when either C1 or C2 experiences leakage current anomaly, the positive and negative bus voltages are unequal compared to when neither capacitor is experiencing leakage current anomaly. This leads to a midpoint potential imbalance, and the midpoint current will also change due to midpoint balance control. For example, as... Figure 3 As shown, compared to time t1, due to the abnormal leakage current of the first film capacitor C1, the positive bus voltage decreases and the negative bus voltage increases at time t3, while the midpoint current increases due to midpoint potential balance control. Therefore, the changes in positive and negative bus voltages and the midpoint current between time t3 and time t1 are no longer zero. Thus, when the changes in positive and negative bus voltages and the midpoint current between time t3 and time t1 meet certain conditions, it can be determined that the first film capacitor C1 has an abnormal leakage current. Similarly, as... Figure 4As shown, compared to time t1', due to the abnormal leakage current of the second film capacitor C2, the positive bus voltage rises and the negative bus voltage falls at time t3', while the midpoint current decreases due to midpoint potential balance control. Therefore, the changes in positive and negative bus voltages and the midpoint current between time t3' and t1' are no longer zero. Thus, when certain conditions are met, it can be determined that the second film capacitor C2 has an abnormal leakage current. The conditions for these changes will be detailed below and will not be elaborated upon here. Therefore, it is evident that the presence of abnormal leakage current in either the first film capacitor C1 or the second film capacitor C2 can be determined based on the changes in midpoint current and positive and negative voltages between two time points.

[0075] In some feasible implementations, the inverter circuit may include a single-phase inverter circuit, a two-phase inverter circuit, a three-phase inverter circuit, a three-phase four-wire inverter circuit, etc. The specific topology of the inverter circuit can be determined according to the actual application scenario and is not limited here. The structure of the inverter circuit can be a three-level inverter circuit or an inverter circuit with more than three levels; there is no limitation in this regard. For ease of description, the following will use a three-phase three-level inverter circuit as an example for detailed description. The structure of the three-phase three-level inverter circuit can adopt a T-type three-level topology or an I-type three-level topology. The following will describe the inverter circuit as a three-phase three-level inverter circuit using a T-type topology. See also Figure 5 , Figure 5 This is another structural schematic diagram of the photovoltaic power generation system provided in the embodiments of this application. For example... Figure 5As shown, the inverter circuit may include an A-phase bridge arm, a B-phase bridge arm, and a C-phase bridge arm. The A-phase, B-phase, and C-phase bridge arms correspond to the A-phase, B-phase, and C-phase outputs of the inverter circuit, respectively. All three bridge arms employ a T-type topology. The A-phase bridge arm includes a first switch Q11 and a fourth switch Q14. A second switch Q12 and a third switch Q13 are connected in series between the series connection terminal O1 of the first switch Q11 and the series connection terminal N of the first thin-film capacitor C1 and the second thin-film capacitor C2. The series connection terminal O1 of the first switch Q11 and the fourth switch Q14 is the midpoint of the A-phase bridge arm. It can be understood that O1 can be connected to the midpoint N via the second switch Q12 and the third switch Q13 connected in reverse series. The aforementioned second switch Q12 and third switch Q13 are connected in reverse series. This can mean that the diodes connected in parallel on the second switch Q12 and the third switch Q13 have opposite directions of current conduction. In other words, the diodes connected in parallel on the second switch Q12 and the third switch Q13 have opposite current conduction directions. These diodes can be reverse-biased diodes included in the second switch Q12 and the third switch Q13. For example, the diode connected in parallel on the second switch Q12 can conduct current flowing from the connection terminal of the first film capacitor C1 and the second film capacitor C2 to the connection terminal of the first switch Q11 and the fourth switch Q14, while the diode connected in parallel on the third switch Q13 can conduct current flowing from the connection terminal of the first switch Q11 and the fourth switch Q14 to the connection terminal of the first film capacitor C1 and the second film capacitor C2. Here, in the aforementioned reverse-connected second switch Q12 and third switch Q13, the third switch Q13 can be connected to the connection terminal of the first film capacitor C1 and the second film capacitor C2, or the second switch Q12 can be connected to the connection terminal of the first film capacitor C1 and the second film capacitor C2. This embodiment uses the connection terminal of the second switch Q12 to the first film capacitor C1 and the second film capacitor C2 as an example, and will not be elaborated further below. The structures of the B-phase bridge arm and the C-phase bridge arm are the same as those of the A-phase bridge arm, and will not be elaborated further here. In the B-phase bridge arm, the series connection terminal O2 of Q21 and Q24 is the midpoint of the B-phase bridge arm, and is connected to the series connection terminal N of the first film capacitor C1 and the second film capacitor C2 through the reverse-connected Q22 and Q23. In the C-phase bridge arm, the series connection terminal O3 of Q31 and Q34 is the midpoint of the C-phase bridge arm, and is connected to the series connection terminal N of the first film capacitor C1 and the second film capacitor C2 through the reverse-connected Q32 and Q33.

[0076] The switching transistors in the inverter circuit can be insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), gate-turn-off thyristors (GTOs), integrated gate-commutated thyristors (IGCTs), etc.

[0077] In some feasible implementations, such as Figure 5 As shown, the control unit can be electrically connected to the positive DC bus BUS+, the negative DC bus BUS-, and the neutral point N to sample the positive bus voltage, negative bus voltage, and neutral point current. Optionally, in the case of a three-phase three-level inverter circuit, the control unit can be electrically connected to the output terminals (A-phase output terminal, B-phase output terminal, C-phase output terminal) of the inverter circuit to sample the three-phase output voltages (i.e., A-phase output voltage Ua, B-phase output voltage Ub, C-phase output voltage Uc) and three-phase output currents (i.e., A-phase output current ia, B-phase output current ib, C-phase output current ic), and calculate the neutral point current based on the three-phase output voltages and currents. The process of calculating the neutral point current based on the three-phase output voltages and currents is familiar to those skilled in the art and will not be elaborated upon here. Alternatively, the control unit can acquire the positive bus voltage, negative bus voltage, and neutral point current through an external sampling module. Simultaneously, this sampling module is communicatively connected to the control unit and can send the sampled positive bus voltage, negative bus voltage, and neutral point current to the controller. Optionally, the control unit can also acquire the three-phase output voltage and three-phase output current through an external sampling module, and send the sampled three-phase output voltage and three-phase output current to the control unit through the sampling module connected in communication with the control unit. The control unit can calculate the midpoint current based on the three-phase output voltage and three-phase output current. Alternatively, Hall sensors can be added at the positive DC bus BUS+, negative DC bus BUS-, and midpoint N. The Hall sensors can sample the positive bus voltage, negative bus voltage, and midpoint current. Optionally, Hall sensors can also be added at the three-phase output terminals to sample the three-phase output voltage and three-phase output current. Further, the control unit can determine whether the first film capacitor C1 and the second film capacitor C2 have abnormal leakage current based on the changes in the positive and negative bus voltages and the changes in the midpoint current (hereinafter referred to as current changes). In some feasible embodiments, Hall sensors can be added at the positive DC bus BUS+, negative DC bus BUS-, and midpoint N, or at the three-phase output terminals.

[0078] It is understood that the above are merely examples, and the embodiments of this application do not limit the implementation method of the control unit to obtain the changes in positive and negative bus voltage and current.

[0079] like Figure 5 As shown, by controlling the on and off states of each switch in the three-phase three-level inverter circuit, the three-phase three-level inverter circuit can be controlled to continuously supply AC power to the grid or load. Taking phase A as an example, assuming the output voltage of the DC input unit is Udc, there are three switching modes. When the first switch Q11 and the second switch Q12 are on, and the third switch Q13 and the fourth switch Q14 are off, the output voltage of phase A is Udc / 2. When the first switch Q11 and the fourth switch Q14 are off, and the second switch Q12 and the third switch Q13 are on, the output voltage of phase A is 0. When the first switch Q11 and the second switch Q12 are off, and the third switch Q13 and the fourth switch Q14 are on, the output voltage of phase A is -Udc / 2. When the three-phase three-level inverter circuit is operating normally, the switches in the A-phase, B-phase, and C-phase bridge arms can cycle through three switching modes within one cycle, making the A, B, and C-phase output voltages a set of sinusoidal waves with a 120° phase difference. The three-phase output currents should also be in phase and frequency with their corresponding three-phase output voltages; that is, the A-phase output current is in phase with the A-phase output voltage, the B-phase output current is in phase with the B-phase output voltage, and the C-phase output current is in phase with the C-phase output voltage. At this time, according to Kirchhoff's current law, the sum of the instantaneous values ​​of the three-phase output currents is zero, meaning the current flowing into the midpoint N is equal to the current flowing out of the midpoint N. The sum of the instantaneous values ​​of the three-phase output voltages is also zero. Together, they constitute a balanced three-phase system, achieving stable power transmission. Therefore, due to the cyclic switching of the switching modes, the three-phase output voltages and three-phase output currents of phases A, B, and C change. Thus, the neutral point current can be calculated in real time based on the A-phase output voltage Ua, B-phase output voltage Ub, C-phase output voltage Uc, A-phase output current ia, B-phase output current ib, and C-phase output current ic. Here, Ua, Ub, and Uc are the actual values ​​of the three-phase output voltages A, B, and C. Please refer to the following formula for details:

[0080]

[0081] Where ωt is the phase angle of the output voltage of the three-phase three-level inverter circuit, u j ′ It can be the per-unit value of the three-phase output voltages A, B, and C, u j The value can be the actual output voltage of phases A, B, and C, where j can be a, b, or c, representing the bridge arms of phases A, B, and C respectively, and u... base It can be used as a reference voltage.

[0082] Here, the per-unit values ​​of the three-phase output voltages A, B, and C can be dimensionless values ​​representing the relative magnitudes of the three-phase output voltages A, B, and C. The reference voltage can be preset, and the specific value can be determined according to the actual application scenario, without further restrictions here. For a three-phase three-level inverter circuit, since the three-phase output voltages A, B, and C are a set of sine waves with a phase difference of 120°, one cycle of [0, 2π] can be divided into 6 intervals as shown in formula (5), namely [0, π / 3], [π / 3, 2π / 3], [2π / 3, π], [π, 4π / 3], [4π / 3, 5π / 3], and [5π / 3, 2π]. Here, the aforementioned cycle can be the fundamental period of the grid voltage connected to the output terminal of the three-phase three-level inverter circuit or the fundamental period of the voltage required by the load connected to the output terminal of the three-phase three-level inverter circuit. However, the grid voltage or the load voltage of a nonlinear load may contain harmonic components. These harmonic components can cause distortions in the three-phase output voltage and three-phase output current, leading to periodic distortions in the midpoint potential and midpoint current. Therefore, when determining whether there is an abnormal leakage current in the first film capacitor C1 or the second film capacitor C2 based on the changes in current and the changes in positive and negative bus voltages, it is also necessary to eliminate the interference from the changes in midpoint potential and midpoint current caused by harmonics. In summary, since the changes in midpoint potential and midpoint current caused by harmonics are periodic, by limiting the time interval between two time points to an integer multiple of a fundamental period, we can obtain two time points within the same interval of different periods. The changes in current and positive and negative bus voltages caused by harmonics between these two time points are the same, thus eliminating the interference from harmonics.

[0083] In specific implementation, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors C1 and C2 between the first and second time points in each time group within the target detection time. This is done when the absolute value of the change in current flowing through the series connection of the first film capacitor C1 and the second film capacitor C2 is greater than or equal to a first change, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group is greater than or equal to the target bus voltage change. In this case, the control unit may also output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors C1 and C2, and / or control the inverter circuit to stop operating. The time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage. Here, the control unit can output a detection result indicating that at least one of the first thin-film capacitors C1 and C2 has an abnormal leakage current; alternatively, the control unit can control the inverter circuit to stop operating; or, the control unit can output a detection result indicating that at least one of the first thin-film capacitors C1 and C2 has an abnormal leakage current and control the inverter circuit to stop operating. In some feasible embodiments, the control unit controlling the inverter circuit to stop operating can be a transient blocking of the inverter circuit. For example, as... Figure 5 The control unit shown can control the transient blocking of the three-level inverter circuit. The three-level inverter circuit can receive pulse-width modulation (PWM) signals from a host computer (such as the driver circuit of the three-level inverter circuit) to control the operation of the switching transistors in each phase arm. This PWM signal is also called a PWM wave. Correspondingly, blocking can mean that the three-level inverter circuit stops receiving PWM waves, thereby turning off the switching transistors in each phase arm. Optionally, the control unit can control the inverter circuit to stop operating by stopping the midpoint balance control.

[0084] The fundamental period can be the fundamental period of the grid voltage connected to the output terminal of the three-phase three-level inverter circuit or the fundamental period of the voltage required by the load connected to the output terminal of the three-phase three-level inverter circuit. For example, ... Figure 5 As shown, the output of the three-phase three-level inverter circuit is connected to the power grid. Therefore, the fundamental period can be the fundamental period of the power grid voltage. The series connection of the first film capacitor C1 and the second film capacitor C2 can be the midpoint N, and the current flowing through the series connection of the first film capacitor C1 and the second film capacitor C2 can be the midpoint current.

[0085] In some feasible implementations, the current change corresponding to each time group can be the difference between the current value of the first current flowing through the series connection terminal at the first time point and the current value of the second current flowing through the series connection terminal at the second time point in each time group.

[0086] For example, taking a time group as an example, the first time point of this time group can be denoted as T1, and the second time point can be denoted as T2. If the first time point T1 is within [0, π / 3], then the second time point T2 can be [2kπ, π / 3 + 2kπ], where k is a positive integer. The first current flowing through the series connection terminal (i.e., the midpoint N) at the first time point T1 can be denoted as io(T1), and the second current flowing through the series connection terminal (i.e., the midpoint N) at the second time point T2 can be denoted as io(T2). The change in current calculated based on the first current io(T1) and the second current io(T2) can be denoted as Δi. o .by Figure 3 For example, if time t1 is the first time point T1 and time t3 is the second time point T2, the time interval between time t1 and time t3 can be an integer multiple of the fundamental period of the grid voltage. Taking multiple time groups as an example, if the first time point T1 of each time group is within [0, π / 3], then the second time point T2 of each time group can be [2kπ, π / 3 + 2kπ], where k is a positive integer. Here, the target detection time can be denoted as t0, and the time group within the target detection time can represent the sampling duration of the first time point T1 and the second time point T2 in each time group. Figure 3 For example, each time group within the target detection time can be represented by the first time point T1 in each time group being within [t1, t1+t0], where [t1, t1+t0] is the sampling interval for the first time point T1 in each time group, and the second time point T2 in each time group being within [t3, t3+t0], where [t3, t3+t0] is the sampling interval for the second time point T2 in each time group. Similarly, taking... Figure 4 For example, each time group within the target detection time can be represented by the first time point T1 in each time group being within [t1', t1'+t0], where [t1', t1'+t0] is the sampling interval of the first time point T1 in each time group, and the second time point T2 in each time group being within [t3', t3'+t0], where [t3', t3'+t0] is the sampling interval of the second time point T2 in each time group. For ease of description, the following text uses one time group as an example.

[0087] Furthermore, at time t3, the first thin-film capacitor C1 exhibits an abnormal leakage current, with the first current io(T1) at the first time point T1 being less than the second current io(T2) at the second time point T2. Therefore, the change in current can be calculated using formula (7) or formula (8). It should be understood that the formula for calculating the change in current corresponding to multiple time groups is the same as that for the change in current corresponding to a single time group, and will not be elaborated upon here.

[0088] Δi o =io(T2)-io(T1)(7)

[0089] Δi o =io(T1)-io(T2)(8)

[0090] Furthermore, the changes in positive and negative bus voltages corresponding to each time group can be determined based on the voltage difference between the positive and negative bus voltages obtained at the first time point T1 and the voltage difference between the positive and negative bus voltages obtained at the second time point T2.

[0091] For example, the positive bus voltage obtained at the first time point T1 can be denoted as Uc1(T1), the negative bus voltage obtained at the first time point T1 can be denoted as Uc2(T1), and the voltage difference between the positive and negative bus voltages at the first time point T1 can be denoted as ΔU. bus1 The positive bus voltage obtained at the second time point T2 can be denoted as Uc1(T2), and the negative bus voltage obtained at the second time point T2 can be denoted as Uc2(T2). The voltage difference between the negative bus voltages at the second time point T2 can be denoted as ΔU. bus2 Among them, according to ΔU bus1 and ΔU bus2 The resulting changes in positive and negative bus voltages can be denoted as ΔU. err .by Figure 3For example, at time t3, the first thin-film capacitor C1 has an abnormal leakage current. Compared with time t1, the positive bus voltage decreases and the negative bus voltage increases at time t3. That is, the positive and negative bus voltages Uc1(T1) at the first time point T1 are greater than the positive bus voltage Uc1(T2) at the second time point T2, and the negative bus voltage Uc2(T1) at the first time point T1 is less than the negative bus voltage Uc2(T2) at the second time point T2. Then, the voltage difference between the positive and negative bus voltages at the first time point T1 can be found in the following formula (9), the voltage difference between the positive and negative bus voltages at the second time point T2 can be found in the following formula (11), and the change in positive and negative bus voltages can be found in the following formula (13). Alternatively, the voltage difference between the positive and negative bus voltages at the first time point can be found in the following formula (9), the voltage difference between the positive and negative bus voltages at the second time point T2 can be found in the following formula (11), and the change in positive and negative bus voltages can be found in the following formula (14). The voltage difference between the positive and negative bus voltages at the first time point T1 can be found in formula (10), the voltage difference between the positive and negative bus voltages at the second time point T2 can be found in formula (12), and the change in positive and negative bus voltages can be found in formula (13). Alternatively, the voltage difference between the positive and negative bus voltages at the first time point T1 can be found in formula (10), the voltage difference between the positive and negative bus voltages at the second time point T2 can be found in formula (12), and the change in positive and negative bus voltages can be found in formula (14). It should be understood that the calculation methods for the voltage difference between the positive and negative bus voltages at the first time point T1, the voltage difference between the positive and negative bus voltages at the second time point T2, and the change in positive and negative bus voltages can be determined according to the actual application scenario, and are not restricted here. It should be understood that the calculation formulas for the change in positive and negative bus voltages corresponding to multiple time groups are the same as those for the change in positive and negative bus voltages corresponding to one time group, and will not be elaborated further here.

[0092] △Ubus1=UC1(T1)-UC2(T1)(9)

[0093] △Ubus1=UC2(T1)-UC1(T1)(10)

[0094] △Ubus2=UC1(T2)-UC2(T2)(11)

[0095] △Ubus2=UC2(T2)-UC1(T2)(12)

[0096] △Uerr=△Ubus2-△Ubus1(13)

[0097] △Uerr=△Ubus1-△Ubus2(14)

[0098] In summary, the leakage current abnormality of the first film capacitor C1 or the second film capacitor C2 can be determined based on the change in the midpoint current and the change in the positive and negative bus voltages. For details, please refer to the leakage current abnormality detection table, as shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] As shown in Table 1, the changes in current Δio and the changes in voltage between the positive and negative busbars ΔUerr can have positive or negative values ​​due to different calculation methods. For example... Figure 3 and Figure 4 It is known that when either the first film capacitor C1 or the second film capacitor C2 has an abnormal leakage current, the positive bus voltage and the negative bus voltage exhibit different trends. Therefore, when the trends of the positive and negative bus voltages satisfy the trends observed when either the first or second film capacitor C2 has an abnormal leakage current, the detection result of at least one of the first and second film capacitors having an abnormal leakage current can be determined when the absolute value of the current change Δio corresponding to each time group is greater than or equal to the first change Idelta, and the absolute value of the changes in the positive and negative bus voltages corresponding to each time group is greater than or equal to the target bus voltage change Udelta. Here, when only one of the first and second film capacitors has an abnormal leakage current, the film capacitor with the abnormal leakage current can be detected based on the trends of the positive and negative bus voltages, the current change Δio, and the changes in the positive and negative bus voltages ΔUerr. When both the first film capacitor C1 and the second film capacitor C2 have abnormal leakage current, it can be determined which film capacitor has a more severe leakage current abnormality based on the changing trends of the positive and negative bus voltages, the current change Δio, and the changes in the positive and negative bus voltages.

[0103] In some feasible implementations, the first change and the target bus voltage change can be preset. Since the leakage current of the film capacitor during early self-healing is less than that during later aging, the first change and the target bus voltage change can be set to different values ​​depending on the aging state of the film capacitor, in order to detect abnormal leakage current in the film capacitor in a timely manner.

[0104] Understandably, the positive and negative bus voltages exhibit different trends when the first film capacitor C1 or the second film capacitor C2 has an abnormal leakage current compared to when it does not, and both the current change and the changes in both positive and negative bus voltages also change. Therefore, if the trends of the positive and negative bus voltages satisfy the trends when either the first or second film capacitor C1 has an abnormal leakage current, and the absolute values ​​of the current change and the absolute values ​​of the changes in the positive and negative bus voltages meet certain conditions, then it can be determined that at least one film capacitor has an abnormal leakage current. Thus, the trends of the positive and negative bus voltages, the absolute values ​​of the current change, and the changes in the positive and negative bus voltages can reflect the self-healing status of the film capacitors in real time, offering advantages such as high detection accuracy, high efficiency, and low cost. In addition, during the self-healing process of the thin film capacitor, if any abnormal leakage current is detected in any thin film capacitor, a protection strategy is executed in a timely manner, such as transient blocking to stop the inverter circuit from working. This can prevent excessive leakage current from causing the thin film capacitor to fail, thereby causing a power conversion device malfunction and ensuring the stability of the power generation of the power conversion device.

[0105] In some feasible implementations, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit may output a detection result of abnormal leakage current in the first film capacitor C1 when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change.

[0106] like Figure 3It can be seen that the first film capacitor C1 did not exhibit abnormal leakage current at time t1, but it did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Taking the first and second time points in a time group as an example, where the first time point is t1 and the second time point is t3, if the positive bus voltage of this time group decreases from t1 through t3, and the negative bus voltage increases from t1 through t3, and the absolute value of the current change corresponding to this time group is greater than or equal to the first change, and the absolute values ​​of the positive and negative bus voltage changes corresponding to this time group are greater than or equal to the target bus voltage change, then it can be determined that the first film capacitor C1 has an abnormal leakage current. Therefore, it can be deduced that if the positive bus voltage of each time group decreases from the first time point to the second time point, and the negative bus voltage of each time group increases from the first time point to the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, then it can be determined that the first thin film capacitor C1 has an abnormal leakage current.

[0107] It is understandable that when the first film capacitor C1 does not exhibit leakage current anomaly, since the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is 0, and the midpoint current remains constant; that is, the change in current and the change in positive and negative bus voltages remain constant. When the first film capacitor C1 exhibits leakage current anomaly, the positive bus voltage decreases compared to when the first film capacitor C1 does not exhibit leakage current anomaly, and the negative bus voltage increases compared to when the first film capacitor C1 does not exhibit leakage current anomaly. The voltage difference between the positive and negative bus voltages is not 0, and the midpoint current is no longer constant; that is, both the change in current and the change in positive and negative bus voltages change. Therefore, when the positive and negative bus voltages in each time group satisfy the above-mentioned trend, the presence of leakage current anomaly in the first film capacitor C1 can be determined based on the absolute value of the change in current and the absolute value of the change in positive and negative bus voltages corresponding to each time group. It is evident that the changing trends of the positive and negative bus voltages, the changes in current, and the changes in both positive and negative bus voltages can reflect the leakage current status of the film capacitor in real time. This allows for timely and rapid detection of any abnormal leakage current, and also enables the location of the film capacitor with the abnormal leakage current, facilitating the replacement of the film capacitor by technicians.

[0108] In some feasible implementations, when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating that the second thin-film capacitor C2 has an abnormal leakage current when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change.

[0109] like Figure 4 It can be seen that the second film capacitor C2 did not exhibit abnormal leakage current at time t1', but it did at time t3'. The positive bus voltage at time t3' was higher than that at time t1', and the negative bus voltage at time t3' was lower than that at time t1'. Taking the first and second time points in a time group as an example, where the first time point is t1' and the second time point is t3', if the positive bus voltage of this time group increases from t1' through t3', and the negative bus voltage decreases from t1' through t3', and the absolute value of the current change corresponding to this time group is greater than or equal to the first change, and the absolute values ​​of the positive and negative bus voltage changes corresponding to this time group are greater than or equal to the target bus voltage change, then it can be determined that the second film capacitor C2 has an abnormal leakage current. Therefore, it can be deduced that if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, then it can be determined that the second thin film capacitor C2 has an abnormal leakage current.

[0110] It is understandable that when the second film capacitor C2 does not exhibit leakage current anomalies, since the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is zero, and the midpoint current remains constant; that is, the changes in current and the changes in positive and negative bus voltages remain constant. When the second film capacitor C2 exhibits leakage current anomalies, the positive bus voltage increases compared to when the second film capacitor C2 does not exhibit leakage current anomalies, and the negative bus voltage decreases compared to when the second film capacitor C2 does not exhibit leakage current anomalies. The voltage difference between the positive and negative bus voltages is no longer zero, and the midpoint current is no longer constant; that is, both the changes in current and the changes in positive and negative bus voltages change. Therefore, when the positive and negative bus voltages in each time group satisfy the above-mentioned trend, the presence of leakage current anomalies in the second film capacitor C2 can be determined based on the absolute values ​​of the current changes and the absolute values ​​of the positive and negative bus voltage changes corresponding to each time group. It is evident that the changing trends of the positive and negative bus voltages, the changes in current, and the changes in both positive and negative bus voltages can reflect the leakage current status of the film capacitor in real time. This allows for timely and rapid detection of any abnormal leakage current, and also enables the location of the film capacitor with the abnormal leakage current, facilitating the replacement of the film capacitor by technicians.

[0111] Please refer to Table 1 again. When the changing trends of the positive and negative bus voltages satisfy the trend of either the first film capacitor C1 or the second film capacitor C2 exhibiting abnormal leakage current, and the absolute value of the positive and negative bus voltage changes ΔUerr is greater than or equal to the target bus voltage change Udelta, the film capacitor exhibiting abnormal leakage current can be determined based on the current change Δio. Specifically, taking a time group as an example, when Δio = io(T2) - io(T1) and the first film capacitor C1 exhibits abnormal leakage current, Δio is positive; when Δio = io(T2) - io(T1) and the second film capacitor C2 exhibits abnormal leakage current, Δio is negative. Figure 3 As shown, the first thin-film capacitor C1 has an abnormal leakage current. If the second time point is t3, the first time point is t1, io(T2) is the midpoint current at t3, and io(T1) is the midpoint current at t1, then Δio is positive when Δio = io(T2) - io(T1). Figure 4 As shown, the second thin-film capacitor C2 has an abnormal leakage current. If the second time point is t3' and the first time point is t1', io(T2) is the midpoint current at t3' and io(T1) is the midpoint current at t1', then when Δio = io(T2) - io(T1), Δio is a negative value.

[0112] As shown in Table 1, when Δio = io(T1) - io(T2) and the first film capacitor C1 has an abnormal leakage current, Δio is negative; when the second film capacitor C2 has an abnormal leakage current, Δio is positive. Figure 3 As shown, the first thin-film capacitor C1 has an abnormal leakage current. If the second time point is t3, the first time point is t1, io(T2) is the midpoint current at t3, and io(T1) is the midpoint current at t1, then Δio is negative when Δio = io(T1) - io(T2). Figure 4 As shown, the second thin-film capacitor C2 has an abnormal leakage current. If the second time point is t3' and the first time point is t1', io(T2) is the midpoint current at t3' and io(T1) is the midpoint current at t1', then when Δio = io(T1) - io(T2), Δio is a positive value.

[0113] Therefore, it can be deduced that when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, Δio = io(T2) - io(T1), and the absolute values ​​of the changes in positive and negative bus voltages ΔUerr are both greater than or equal to the target bus voltage change Udelta, if the current change Δio is positive and greater than or equal to the first change Idelta, it can be determined that the first film capacitor C1 has an abnormal leakage current. Conversely, when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, and the current change Δio is negative and less than or equal to the negative of the first change Idelta, it can be determined that the second film capacitor C2 has an abnormal leakage current.

[0114] Similarly, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, with Δio = io(T1) - io(T2) and the absolute values ​​of the positive and negative bus voltage changes ΔUerr both greater than or equal to the target bus voltage change Udelta, if the current change Δio is negative and less than or equal to the negative of the first change Idelta, it can be determined that the first film capacitor C1 has an abnormal leakage current. Conversely, when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, with the current change Δio being positive and greater than or equal to the first change Idelta, it can be determined that the second film capacitor C2 has an abnormal leakage current.

[0115] In summary, when the changing trends of the positive and negative bus voltages satisfy the changing trends of either the first film capacitor C1 or the second film capacitor C2 with abnormal leakage current, and when the absolute values ​​of the positive and negative bus voltage changes ΔUerr are both greater than or equal to the target bus voltage change Udelta, at least one film capacitor with abnormal leakage current can be detected in a timely manner based on the calculation method of the current change Δio and the sign of the current change Δio. Furthermore, the specific film capacitor with abnormal leakage current can be located.

[0116] Besides the possibility that leakage current anomalies in the first film capacitor C1 or the second film capacitor C2 could cause changes in the positive and negative bus voltage and current, variations in the parameters of the switching devices in the inverter circuit, or aging of the switching devices, can also cause changes in the positive and negative bus voltage and current. Therefore, to reduce the interference of individual abnormal data, the changes in positive and negative bus voltage and current corresponding to multiple consecutive time groups can be detected to improve the accuracy of leakage current anomaly detection.

[0117] In some feasible implementations, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit may, within the target detection time, output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors C1 and C2, and / or control the inverter circuit to stop operating, when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period. Specifically, to avoid three-phase output voltage imbalance or three-phase output current imbalance caused by harmonic components of the grid voltage or load voltage, the target detection time may be greater than the fundamental period.

[0118] like Figure 3 As shown, each time group within the target detection time can be represented by the first time point T1 within each time group being located within [t1, t1+t0], where [t1, t1+t0] is the sampling interval for the first time point T1 within each time group, and the second time point T2 within each time group being located within [t3, t3+t0], where [t3, t3+t0] is the sampling interval for the second time point T2 within each time group. Similarly, as... Figure 4As shown, each time group within the target detection time indicates that the first time point T1 in each time group is within [t1', t1'+t0], where [t1', t1'+t0] is the sampling interval of the first time point T1 in each time group, and the second time point T2 in each time group is within [t3', t3'+t0], where [t3', t3'+t0] is the sampling interval of the second time point T2 in each time group. It should be understood that if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, this indicates that the absolute value of the current change is greater than or equal to the first change, and the duration for which the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change is the target detection time. Therefore, if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the duration of the change in the target bus voltage is greater than one fundamental period, then it can be determined that at least one of the first thin film capacitor C1 and the second thin film capacitor C2 has an abnormal leakage current.

[0119] It is understandable that the current changes and the positive and negative bus voltage changes corresponding to each time group may abruptly change, causing the absolute value of the current change in each time group to be greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes in each time group to be greater than or equal to the target bus voltage change. Therefore, it is possible to detect whether the absolute value of the current change in each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes in each time group is continuously greater than or equal to the target bus voltage change. When the positive and negative bus voltages of each time group meet the trend of abnormal leakage current of the first film capacitor C1 or the second film capacitor C2, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, it can be determined whether the first film capacitor C1 or the second film capacitor C2 has abnormal leakage current. This allows for timely and rapid detection of abnormal leakage current and location of the film capacitor with abnormal leakage current, thus improving the accuracy of abnormal leakage current detection.

[0120] In some feasible implementations, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit may output a detection result indicating that the first thin-film capacitor C1 has an abnormal leakage current when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

[0121] like Figure 3 It can be seen that the first film capacitor C1 did not exhibit abnormal leakage current at time t1, but it did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Assuming that the first time point of each time group is within the sampling interval [t1, t1+t0] and the second time point of each time group is within the sampling interval [t3, t3+t0], then if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the duration of the absolute value of the positive and negative bus voltage changes corresponding to each time group being greater than or equal to the target bus voltage change is greater than one fundamental period, then it can be determined that the first film capacitor C1 has an abnormal leakage current.

[0122] Understandably, when the first film capacitor C1 does not exhibit leakage current anomalies, the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is 0, and the midpoint current remains constant; that is, the changes in current and the changes in positive and negative bus voltages remain constant. When the first film capacitor C1 exhibits leakage current anomalies, the positive bus voltage decreases compared to when the first film capacitor C1 does not exhibit leakage current anomalies, and the negative bus voltage increases compared to when the first film capacitor C1 does not exhibit leakage current anomalies. The voltage difference between the positive and negative bus voltages is not 0, and the midpoint current is no longer constant; that is, both the changes in current and the changes in positive and negative bus voltages change. By detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0123] In some feasible implementations, when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, the control unit may output a detection result indicating that the second thin-film capacitor C2 has an abnormal leakage current when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

[0124] like Figure 4 It can be seen that the second film capacitor C2 did not exhibit leakage current abnormality at time t1', but did at time t3'. The positive bus voltage at time t3' decreased compared to the positive bus voltage at time t1', while the negative bus voltage at time t3' increased compared to the negative bus voltage at time t1'. Assuming that the first time point of each time group is within the sampling interval [t1', t1'+t0], and the second time point of each time group is within the sampling interval [t3', t3'+t0], then if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the duration of the absolute value of the positive and negative bus voltage changes corresponding to each time group being greater than or equal to the target bus voltage change is greater than one fundamental period, then it can be determined that the second film capacitor C2 has leakage current abnormality.

[0125] Understandably, when the second film capacitor C2 does not exhibit leakage current anomalies, since the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is zero, and the midpoint current remains constant; that is, the change in current and the changes in positive and negative bus voltages remain constant. When the second film capacitor C2 exhibits leakage current anomalies, the positive bus voltage increases compared to when the second film capacitor C2 does not exhibit leakage current anomalies, while the negative bus voltage decreases compared to when the second film capacitor C2 does not exhibit leakage current anomalies. The voltage difference between the positive and negative bus voltages is no longer zero, and the midpoint current is no longer constant; that is, both the change in current and the changes in positive and negative bus voltages change. By detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0126] In one possible implementation, the inverter circuit is connected to the DC input unit via a DC disconnectable switch and to the power grid via a grid-connected relay. During the inverter circuit's shutdown process, the control unit can, when the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to a preset voltage change, control the DC disconnectable switch and the grid-connected relay to disconnect the inverter circuit from the DC input unit and the power grid; the preset voltage change is greater than the target bus voltage change. Specifically, the preset voltage change is greater than the target bus voltage change.

[0127] It should be understood that the control unit can temporarily stop receiving PWM waves from the host computer when it detects abnormal changes in the current or positive / negative bus voltage of the first film capacitor C1 or the second film capacitor C2, thereby controlling the switching transistors in the inverter circuit to stop working. Alternatively, the control unit can temporarily maintain balance control at the stop point to control the inverter circuit to stop working. Theoretically, during the inverter circuit shutdown process, the capacitor voltage of the first film capacitor C1 and the capacitor voltage of the second film capacitor C2 should no longer change, i.e., the positive and negative bus voltages should no longer change. However, if during the inverter circuit shutdown process, the absolute value of the positive and negative bus voltage changes still increases and is greater than or equal to the preset voltage change, it can be determined that the first film capacitor C1 or the second film capacitor C2 still has abnormal leakage current. At this time, the capacitor voltage of the first film capacitor C1 and the capacitor voltage of the second film capacitor C2 are not equal, which may cause the film capacitors to be damaged due to excessive voltage. In summary, during the process of the inverter circuit stopping operation, if the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to the preset voltage change, the inverter circuit can be controlled to disconnect from the DC input unit and the power grid, thus preventing the first film capacitor C1 or the second film capacitor C2 from being damaged due to overvoltage, thereby reducing the possibility of power conversion device failure.

[0128] It should be understood that film capacitors, due to their self-healing properties, may experience multiple leakage current anomalies during power conversion device operation. However, with the accumulation of long-term self-healing, the capacitance of the film capacitor decays, increasing the likelihood of failure. Furthermore, when the power conversion device is subjected to harsh environments such as high temperature and high humidity for extended periods, the insulation aging of the film capacitor is accelerated, further increasing the possibility of failure. Therefore, the abnormal state of the film capacitor can be predicted by the number of leakage current anomalies, thus preventing power conversion device malfunctions caused by film capacitor failure.

[0129] In one possible implementation, the control unit can control the inverter circuit to operate in derating mode when the number of abnormal leakage currents in the thin-film capacitors of the power conversion device reaches a target number within a preset detection time, thereby reducing the output power of the inverter circuit. It is understood that the power conversion device may operate under harsh conditions such as high temperature and high humidity for extended periods. The long-term self-healing accumulation of the thin-film capacitors may accelerate their aging and cause capacitance decay, leading to a decline in their performance. Therefore, the performance status of the thin-film capacitors can be predicted by the number of abnormal leakage currents. When the number of abnormal leakage currents reaches the target number, the inverter circuit can be controlled to operate in derating mode to prevent the thin-film capacitors from burning out due to excessive leakage current. This can, to some extent, slow down the aging rate of the thin-film capacitors and prevent power conversion device failure caused by thin-film capacitor failure, which could then lead to photovoltaic power generation system failure.

[0130] In one possible implementation, the control unit can stop the power converter when the total number of abnormal leakage currents detected in the film capacitors reaches a preset number. Specifically, when the total number of abnormal leakage currents detected in the first film capacitor C1 and the second film capacitor C2 exceeds the preset number, it can be predicted that the safety performance of the first film capacitor C1 and the second film capacitor C2 is low. Therefore, the power converter can be stopped in advance to prevent film capacitor failure and avoid malfunctions in the power converter caused by film capacitor failure. It is understood that when the number of abnormal leakage currents in the film capacitors reaches the limit value of the film capacitors, the safety performance of the film capacitors is low, which may lead to the failure of the film capacitors, resulting in the film capacitors being burned out, and may also cause damage to other electronic components, leading to the spread of the fault. To avoid the above-mentioned fault conditions, the power converter can be stopped in advance when the total number of abnormal leakage currents detected in the film capacitors reaches the preset number, avoiding damage to other electronic components and ensuring the safety of the power converter.

[0131] It should be understood that, in order to reduce the interference of individual abnormal data, the current change corresponding to each time group can be processed, and then the processed current change can be combined to determine leakage current anomaly detection, thereby improving detection efficiency and accuracy. This application provides a power conversion device that can be used in a photovoltaic power generation system. The power conversion device may include a control unit, a positive DC bus BUS+, a negative DC bus BUS-, a first thin-film capacitor C1, a second thin-film capacitor C2, and an inverter circuit. The structure of the power conversion device can be found in [reference needed]. Figure 2 The corresponding implementation examples will not be described in detail hereafter.

[0132] In some feasible implementations, when the positive bus voltage of each time group decreases from the first time point through the second time point and the negative bus voltage of each time group increases from the first time point through the second time point in at least one time group, or when the positive bus voltage of each time group increases from the first time point through the second time point and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit can process the change in current flowing through the series connection of the first thin-film capacitor C1 and the second thin-film capacitor C2 between the first time point and the second time point in each time group within the target detection time to obtain the change in current within the target detection time. If the absolute value of the change in current within the target detection time is greater than or equal to a second change, and the absolute value of the change in positive and negative bus voltage between the first time point and the second time point in each time group is greater than or equal to the target bus voltage change, the control unit outputs a detection result indicating abnormal leakage current in at least one of the first thin-film capacitors C1 and C2, and / or controls the inverter circuit to stop operating. The time interval between the first time point and the second time point in any time group is an integer multiple of the fundamental period of the grid voltage. It should be understood that the calculation methods for current changes and positive and negative bus voltage changes can be found above, and will not be elaborated further here.

[0133] In some feasible implementations, the current change corresponding to each time group can be the difference between the current value of the first current flowing through the series connection terminal at the first time point and the current value of the second current flowing through the series connection terminal at the second time point in each time group.

[0134] For example, if the first time point T1 of each time group is within [0, π / 3], then the second time point T2 of each time group can be [2kπ, π / 3 + 2kπ], where k is a positive integer. Here, the target detection time can be denoted as t0, and the time group within the target detection time can represent the sampling duration of the first time point T1 and the second time point T2 in each time group. Figure 3 For example, each time group within the target detection time can be represented by the first time point T1 in each time group being within [t1, t1+t0], where [t1, t1+t0] is the sampling interval for the first time point T1 in each time group, and the second time point T2 in each time group being within [t3, t3+t0], where [t3, t3+t0] is the sampling interval for the second time point T2 in each time group. Similarly, taking... Figure 4 For example, each time group within the target detection time can be represented as the first time point T1 in each time group being within [t1', t1'+t0], where [t1', t1'+t0] is the sampling interval of the first time point T1 in each time group, and the second time point T2 in each time group being within [t3', t3'+t0], where [t3', t3'+t0] is the sampling interval of the second time point T2 in each time group.

[0135] like Figure 3 As shown, the first film capacitor C1 did not exhibit leakage current abnormality at time t1, but did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Taking the first and second time points in a time group as an example, where the first time point T1 is time t1 and the second time point T2 is time t3, the positive bus voltage in this time group decreases from time t1 through time t3, and the negative bus voltage increases from time t1 through time t3. However, when the first film capacitor C1 exhibits leakage current abnormality across multiple time groups, it's possible that the positive and negative bus voltages in a certain time group do not conform to the above trend. To reduce the false detection rate, the current changes corresponding to each time group can be processed to obtain the current changes within the target detection time. Thus, based on the current changes within the target detection time and the changes in the positive and negative bus voltages corresponding to each time group, it can be determined whether there is a leakage current abnormality in the film capacitor.

[0136] Similarly, such as Figure 4 As shown, the second film capacitor C2 did not exhibit abnormal leakage current at time t1', but it did at time t3'. The positive bus voltage at time t3' decreased compared to the positive bus voltage at time t1', while the negative bus voltage at time t3' increased compared to the negative bus voltage at time t1'. Taking the first and second time points in a time group as an example, where the first time point T1 is time t1' and the second time point T2 is time t3', the positive bus voltage in this time group decreases from time t1' through time t3', while the negative bus voltage increases from time t1 through time t3. However, when the second film capacitor C2 exhibits abnormal leakage current in multiple time groups, it is possible that the positive and negative bus voltages in a certain time group do not meet the above-mentioned trend. In order to reduce the false detection rate, the current change corresponding to each time group can be processed to obtain the current change within the target detection time. In this way, the presence of abnormal leakage current of the film capacitor can be determined based on the current change within the target detection time and the positive and negative bus voltage changes corresponding to each time group.

[0137] Understandably, the positive and negative bus voltages exhibit different trends when the first film capacitor C1 or the second film capacitor C2 has an abnormal leakage current compared to when it does not, and the midpoint current also changes; that is, both the current change and the changes in the positive and negative bus voltages change. Therefore, when the trends of the positive and negative bus voltages match those when the first film capacitor C1 or the second film capacitor C2 has an abnormal leakage current, the presence of an abnormal leakage current in the film capacitors can be determined based on the current change within the target detection time and the corresponding changes in the positive and negative bus voltages for each time group. This allows for timely and rapid detection of abnormal leakage currents and the location of the film capacitor with the abnormal leakage current. Furthermore, processing the current change rate corresponding to each time group to obtain the current change within the target detection time avoids inaccurate detection due to outliers or missing values, thus improving the accuracy of detecting abnormal leakage currents.

[0138] In some feasible implementations, the control unit can integrate the current changes corresponding to each time group within the target detection time to obtain the current change within the target detection time. Here, since the first time point T1 in each time group can be a continuous time point, and the second time point T2 in each time group can also be a continuous time point, the time groups themselves can also be continuous, and the current changes corresponding to each time group can also be continuous. Therefore, the current changes corresponding to each time group within the target detection time can be integrated to obtain the current change within the target detection time. It is understood that when the current changes corresponding to individual time groups are abnormal, the impact on the integrated result of the current changes corresponding to each time group within the target detection time is relatively small. In summary, leakage current anomaly detection can be performed based on the positive and negative bus voltage changes corresponding to each time group and the current changes within the target detection time obtained after integration. Furthermore, by integrating the current changes corresponding to each time group, the data processing accuracy can be further improved. The integrated current changes and positive and negative bus voltage changes can more accurately reflect the self-healing status of the thin-film capacitor, thereby improving the accuracy of leakage current anomaly detection.

[0139] In some feasible implementations, when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit can output a detection result indicating that the first thin-film capacitor C1 has an abnormal leakage current when the absolute value of the change within the target detection time is greater than or equal to the second change, and the absolute value of the changes in the positive and negative bus voltages corresponding to each time group is greater than or equal to the target bus voltage change. Here, the second change can be the product of the first change and the target detection time. It can be understood that if the current change corresponding to each time group is the difference between the midpoint current of the first thin-film capacitor C1 when the leakage current abnormality occurs and the midpoint current of the first thin-film capacitor C1 when the leakage current abnormality does not occur, then the current change corresponding to each time group is positive, and the current change within the target detection time obtained after integration is also positive. If the current change corresponding to each time group is the difference between the midpoint current of the first thin-film capacitor C1 when no leakage current abnormality occurs and the midpoint current of the first thin-film capacitor C1 when leakage current abnormality occurs, then the current change corresponding to each time group is negative, and the current change after integration is also negative. The absolute values ​​of the positive and negative bus voltage changes corresponding to each time group are all greater than 0. By integrating the current changes corresponding to each time group, the problem of inaccurate detection due to outliers or missing values ​​can be avoided, and the data processing accuracy can be further improved. Therefore, based on the current change within the target detection time and the positive and negative bus voltage changes corresponding to each time group, the self-healing status of the thin-film capacitor can be more accurately reflected, thereby improving the accuracy of leakage current abnormality detection.

[0140] In some feasible implementations, when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, the control unit is further configured to output a detection result indicating that the second thin-film capacitor C2 has an abnormal leakage current when the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the changes in the positive and negative bus voltages corresponding to each time group is greater than or equal to the target bus voltage change. Here, the second change can be the product of the first change and the target detection time. It can be understood that if the current change corresponding to each time group is the difference between the midpoint current of the second thin-film capacitor C2 when the leakage current abnormality occurs and the midpoint current of the second thin-film capacitor C2 when the leakage current abnormality does not occur, then the current change corresponding to each time group is negative, and the current change obtained after integration is also negative. If the current change corresponding to each time group is the difference between the midpoint current of the second film capacitor C2 when no leakage current abnormality occurs and the midpoint current of the second film capacitor C2 when leakage current abnormality occurs, then the current change corresponding to each time group is positive, and the current change after integration is also positive. The absolute values ​​of the positive and negative bus voltage changes corresponding to each time group are all greater than 0. In summary, by integrating the current changes corresponding to each time group, the problem of inaccurate detection due to outliers or missing values ​​can be avoided, and the data processing accuracy can be further improved. Therefore, based on the current change within the target detection time and the positive and negative bus voltage changes corresponding to each time group, the self-healing status of the film capacitor can be more accurately reflected, thereby improving the accuracy of detecting leakage current abnormalities.

[0141] In summary, when the first film capacitor C1 does not exhibit leakage current anomaly, since the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is zero, and the midpoint current remains constant; that is, the change in current and the change in positive and negative bus voltages remain constant. When the first film capacitor C1 exhibits leakage current anomaly, the positive bus voltage decreases compared to when the first film capacitor C1 does not exhibit leakage current anomaly, while the negative bus voltage increases compared to when the first film capacitor C1 does not exhibit leakage current anomaly. Similarly, when the second film capacitor C2 does not exhibit leakage current anomaly, since the positive bus voltage and negative bus voltage are equal, the voltage difference between the positive and negative bus voltages is zero, and the midpoint current remains constant; that is, the change in current and the change in positive and negative bus voltages remain constant. When the second film capacitor C2 exhibits leakage current anomaly, the positive bus voltage increases compared to when the second film capacitor C2 does not exhibit leakage current anomaly, while the negative bus voltage decreases compared to when the second film capacitor C2 does not exhibit leakage current anomaly. It is evident that, compared to when the film capacitor is free of leakage current anomalies, the positive bus voltage, negative bus voltage, and midpoint current may increase or decrease when the film capacitor exhibits anomalies. Therefore, when the positive and negative bus voltages in each time group meet the aforementioned trends, the presence of leakage current anomalies in the film capacitor can be determined based on the changes in the midpoint current and the positive and negative bus voltages. This method offers advantages such as high accuracy, high efficiency, and low cost. Furthermore, the changes in positive and negative bus voltages and current can effectively detect whether leakage current anomalies exist during the self-healing process of the film capacitor. Upon detection of leakage current anomalies, timely protection strategies, such as transient blocking, can be implemented to prevent excessive leakage current from causing film capacitor failure and consequently, photovoltaic power generation system malfunctions, thus ensuring the stability of the photovoltaic power generation system.

[0142] Please see Figure 6 , Figure 6 This is a schematic flowchart illustrating a leakage current detection method for a power conversion device provided in an embodiment of this application. The leakage current detection method for a power conversion device provided in this embodiment is applicable to… Figures 2 to 5 The control unit in the corresponding specific implementation. This power conversion device can be used as follows: Figure 2 The photovoltaic power generation system shown is an example. Figure 2As shown, a photovoltaic power generation system may include a DC input unit and a power conversion device. The power conversion device may include a control unit, a positive DC bus BUS+, a negative DC bus BUS-, a first thin-film capacitor C1, a second thin-film capacitor C2, and an inverter circuit. The DC end of the photovoltaic power generation system may include a first output terminal dc1 and a second output terminal dc2 of the DC input unit. The first output terminal dc1 is connected to the positive DC bus BUS+, and the second output terminal dc2 is connected to the negative DC bus BUS-. The first thin-film capacitor C1 and the second thin-film capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The inverter circuit is connected between the positive DC bus BUS+ and the negative DC bus BUS-, and the series connection of the first thin-film capacitor C1 and the second thin-film capacitor C2 is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. The inverter circuit can convert the DC power provided by the DC input unit into AC power and output it to the power grid or load. Here, one end of the first film capacitor C1 is connected to the positive DC bus BUS+, and the other end of the first film capacitor C1 is connected to one end of the second film capacitor C2. The other end of the second film capacitor C2 is connected to the negative DC bus BUS-. The series connection terminal N of the first film capacitor C1 and the second film capacitor C2 is the connection point between the two film capacitors. This series connection terminal N can be the midpoint of the bus (referred to as the midpoint). The DC power provided by the DC input unit can be transmitted to the first film capacitor C1 and the second film capacitor C2 through the positive and negative DC buses (BUS+, BUS-), and stored through the first film capacitor C1 and the second film capacitor C2. The first film capacitor C1 and the second film capacitor C2 can also be used for midpoint balance control to make the capacitor voltage of the first film capacitor C1 equal to the capacitor voltage of the second film capacitor C2. (The last sentence appears to be incomplete and possibly refers to a specific configuration or feature.) Figures 3 to 5 In any power conversion device corresponding to the illustration, the leakage current detection method of the power conversion device provided in this application embodiment may include the following steps:

[0143] S101. Obtain the absolute value of the change in current flowing through the series connection terminal of the first and second film capacitors between the first and second time points in each time group in at least one time group, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group in at least one time group; the time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0144] It is understandable that, such as Figure 3As shown, when neither the first nor the second film capacitor exhibits abnormal leakage current, the capacitor voltage of the first film capacitor is equal to that of the second film capacitor (i.e., the positive bus voltage is equal to the negative bus voltage), and the current flowing into the midpoint is equal to the current flowing out of the midpoint. When either the first or second film capacitor exhibits abnormal leakage current, the capacitor voltage of the first film capacitor is unequal to that of the second film capacitor (i.e., the positive bus voltage is unequal to the negative bus voltage), and the current flowing into the midpoint is unequal to the current flowing out of the midpoint. At this time, the midpoint potential is unbalanced. To balance the midpoint potential, midpoint potential balance control can be used to make the positive bus voltage equal to the negative bus voltage again, and the current flowing into the midpoint equal to the current flowing out of the midpoint again. According to... Figure 3 and Figure 4 It can be seen that when the first film capacitor has an abnormal leakage current, the positive bus voltage decreases compared to when the first film capacitor does not have an abnormal leakage current, while the negative bus voltage increases. Similarly, when the second film capacitor has an abnormal leakage current, the positive bus voltage increases compared to when the first film capacitor does not have an abnormal leakage current, while the negative bus voltage decreases. Therefore, the changes in current and positive and negative bus voltages between the two time periods are no longer zero. Thus, the specific film capacitor with the abnormal leakage current can be determined by observing the changes in current and positive and negative bus voltages for each time group.

[0145] For a detailed implementation of S101, please refer to the above. Figures 2 to 5 The implementation method executed by the control unit is not described in detail in the embodiments of this application.

[0146] S102. When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, output a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or control the inverter circuit to stop working.

[0147] Understandably, since the current change and positive / negative bus voltage change when the first thin-film capacitor has a leakage current anomaly differ from those when the second thin-film capacitor has a leakage current anomaly, it is possible to determine which thin-film capacitor has a leakage current anomaly when the current change and positive / negative bus voltage change meet different preset conditions. Therefore, the positive / negative bus voltage change and current change can reflect the self-healing status of the thin-film capacitor in real time. Furthermore, it can detect whether there is a leakage current anomaly during the self-healing process of the thin-film capacitor, and promptly implement protection strategies, such as transient blocking, when a leakage current anomaly is detected, to prevent excessive leakage current from causing thin-film capacitor failure and thus leading to photovoltaic power generation system malfunctions. This ensures the stability of photovoltaic power generation and has the advantages of high detection accuracy, high efficiency, and low cost.

[0148] For a detailed implementation of S102, please refer to the above. Figures 2 to 5 The implementation method executed by the control unit is not described in detail in the embodiments of this application.

[0149] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second film capacitors is as follows: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the detection result of abnormal leakage current in the first film capacitor is generated when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change.

[0150] like Figure 3It can be seen that the first film capacitor C1 did not exhibit abnormal leakage current at time t1, but it did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Taking the first and second time points in a time group as an example, where the first time point is t1 and the second time point is t3, if the positive bus voltage of this time group decreases from t1 through t3, and the negative bus voltage increases from t1 through t3, and the absolute value of the current change corresponding to this time group is greater than or equal to the first change, and the absolute values ​​of the positive and negative bus voltage changes corresponding to this time group are greater than or equal to the target bus voltage change, then it can be determined that the first film capacitor C1 has an abnormal leakage current. Therefore, it can be deduced that if the positive bus voltage of each time group decreases from the first time point to the second time point, and the negative bus voltage of each time group increases from the first time point to the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, then it can be determined that the first thin film capacitor C1 has an abnormal leakage current.

[0151] Understandably, when the first film capacitor does not exhibit leakage current abnormality, the voltage difference between the positive and negative busbars is zero because the positive and negative busbar voltages are equal, and the midpoint current remains constant. When the first film capacitor exhibits leakage current abnormality, the positive busbar voltage decreases compared to when there is no leakage current abnormality, while the negative busbar voltage increases. The voltage difference between the positive and negative busbars is no longer zero, and the midpoint current no longer remains constant. Therefore, when the positive and negative busbar voltages in each time group meet the above-mentioned trend, the presence of leakage current abnormality in the first film capacitor can be determined based on the absolute values ​​of the current changes and the absolute values ​​of the positive and negative busbar voltage changes in each time group. It is evident that the trends in the positive and negative busbar voltages, the changes in current, and the changes in both positive and negative busbar voltages can reflect the leakage current status of the film capacitor in real time. This allows for timely and rapid detection of leakage current abnormalities and can also pinpoint the film capacitor with the leakage current abnormality, facilitating replacement by technicians.

[0152] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second film capacitors is output as follows: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the detection result of abnormal leakage current in the second film capacitor is output.

[0153] like Figure 4 It can be seen that the second film capacitor C2 did not exhibit abnormal leakage current at time t1', but it did at time t3'. The positive bus voltage at time t3' was higher than that at time t1', and the negative bus voltage at time t3' was lower than that at time t1'. Taking the first and second time points in a time group as an example, where the first time point is t1' and the second time point is t3', if the positive bus voltage of this time group increases from t1' through t3', and the negative bus voltage decreases from t1' through t3', and the absolute value of the current change corresponding to this time group is greater than or equal to the first change, and the absolute values ​​of the positive and negative bus voltage changes corresponding to this time group are greater than or equal to the target bus voltage change, then it can be determined that the second film capacitor C2 has an abnormal leakage current. Therefore, it can be deduced that if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, then it can be determined that the second thin film capacitor C2 has an abnormal leakage current.

[0154] Understandably, when neither the first nor the second film capacitor exhibits leakage current anomalies, the voltage difference between the positive and negative bus voltages is zero because the positive and negative bus voltages are equal, and the midpoint current remains constant. When the second film capacitor exhibits leakage current anomalies, the positive bus voltage increases compared to when the first film capacitor does not exhibit leakage current anomalies, while the negative bus voltage decreases. The voltage difference between the positive and negative bus voltages is no longer zero, and the midpoint current no longer remains constant. Therefore, when the positive and negative bus voltages in each time group meet the above-mentioned trend, the presence of leakage current anomalies in the first film capacitor can be determined based on the absolute values ​​of the current changes and the absolute values ​​of the positive and negative bus voltage changes in each time group. It is evident that the trends in the positive and negative bus voltages, the changes in current, and the changes in both positive and negative bus voltages can reflect the leakage current status of the film capacitors in real time. This allows for timely and rapid detection of leakage current anomalies and also helps locate the film capacitors with leakage current anomalies, facilitating replacement by technicians.

[0155] In one possible implementation, the method further includes: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point; or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, when the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, outputting a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or controlling the inverter circuit to stop working.

[0156] like Figure 3 As shown, each time group within the target detection time can be represented by the first time point T1 within each time group being located within [t1, t1+t0], where [t1, t1+t0] is the sampling interval for the first time point T1 within each time group, and the second time point T2 within each time group being located within [t3, t3+t0], where [t3, t3+t0] is the sampling interval for the second time point T2 within each time group. Similarly, as... Figure 4As shown, each time group within the target detection time indicates that the first time point T1 in each time group is within [t1', t1'+t0], where [t1', t1'+t0] is the sampling interval of the first time point T1 in each time group, and the second time point T2 in each time group is within [t3', t3'+t0], where [t3', t3'+t0] is the sampling interval of the second time point T2 in each time group. It should be understood that if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, this indicates that the absolute value of the current change is greater than or equal to the first change, and the duration for which the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change is the target detection time. Therefore, if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the duration of the change in the target bus voltage is greater than one fundamental period, then it can be determined that at least one of the first thin film capacitor C1 and the second thin film capacitor C2 has an abnormal leakage current.

[0157] It is understandable that the current changes and positive and negative bus voltage changes corresponding to each time group may abruptly change, causing the absolute value of the current change in each time group to be greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes in each time group to be greater than or equal to the target bus voltage change. Therefore, it is possible to detect whether the absolute value of the current change in each time group within the target detection time is consistently greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes in each time group is consistently greater than or equal to the target bus voltage change. When the positive and negative bus voltages in each time group meet the trend of abnormal leakage current in the first or second film capacitor, if the absolute value of the current change in each time group within the target detection time is greater than or equal to the first change and the absolute value of the positive and negative bus voltage changes in each time group is greater than or equal to the target bus voltage change, it can be determined whether the first or second film capacitor has an abnormal leakage current. This allows for timely and rapid detection of abnormal leakage current and pinpointing the film capacitor with the abnormal leakage current, improving the accuracy of abnormal leakage current detection.

[0158] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second thin-film capacitors is as follows: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, and the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of abnormal leakage current in the first thin-film capacitor is generated.

[0159] like Figure 3 It can be seen that the first film capacitor C1 did not exhibit abnormal leakage current at time t1, but it did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Assuming that the first time point of each time group is within the sampling interval [t1, t1+t0] and the second time point of each time group is within the sampling interval [t3, t3+t0], then if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the duration of the absolute value of the positive and negative bus voltage changes corresponding to each time group being greater than or equal to the target bus voltage change is greater than one fundamental period, then it can be determined that the first film capacitor C1 has an abnormal leakage current.

[0160] Understandably, when the first film capacitor does not exhibit leakage current anomalies, the voltage difference between the positive and negative bus voltages is zero because the positive and negative bus voltages are equal, and the midpoint current remains constant. When the first film capacitor exhibits leakage current anomalies, the positive bus voltage decreases compared to when there are no leakage current anomalies, while the negative bus voltage increases. The voltage difference between the positive and negative bus voltages is no longer zero, and the midpoint current no longer remains constant. Therefore, when the positive and negative bus voltages in each time group meet the above-mentioned trend, by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0161] In one possible implementation, the detection result of abnormal leakage current in at least one of the first and second thin-film capacitors is as follows: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of abnormal leakage current in the second thin-film capacitor is generated.

[0162] like Figure 4 It can be seen that the second film capacitor C2 did not exhibit leakage current abnormality at time t1', but did at time t3'. The positive bus voltage at time t3' decreased compared to the positive bus voltage at time t1', while the negative bus voltage at time t3' increased compared to the negative bus voltage at time t1'. Assuming that the first time point of each time group is within the sampling interval [t1', t1'+t0], and the second time point of each time group is within the sampling interval [t3', t3'+t0], then if the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, and if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the duration of the absolute value of the positive and negative bus voltage changes corresponding to each time group being greater than or equal to the target bus voltage change is greater than one fundamental period, then it can be determined that the second film capacitor C2 has leakage current abnormality.

[0163] Understandably, when the second film capacitor does not exhibit leakage current anomalies, the voltage difference between the positive and negative bus voltages is zero because the positive and negative bus voltages are equal, and the midpoint current remains constant. When the first film capacitor exhibits leakage current anomalies, the positive bus voltage increases compared to when there are no leakage current anomalies, while the negative bus voltage decreases. The voltage difference between the positive and negative bus voltages is no longer zero, and the midpoint current no longer remains constant. Therefore, when the positive and negative bus voltages in each time group meet the above-mentioned trend, by detecting whether the absolute value of the current change corresponding to each time group within the target detection time is continuously greater than or equal to the first change and whether the absolute value of the positive and negative bus voltage changes corresponding to each time group is continuously greater than or equal to the target bus voltage change, false detections caused by abrupt changes in the current change and the positive and negative bus voltage changes corresponding to each time group can be avoided, effectively improving detection accuracy.

[0164] In one possible implementation, the inverter circuit is connected to the DC input unit via a DC disconnectable switch, and the inverter circuit is connected to the power grid via a grid-connected relay. The method further includes: during the process of the inverter circuit stopping operation, when the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to a preset voltage change, controlling the DC disconnectable switch and the grid-connected relay to disconnect the inverter circuit from the DC input unit and the power grid; the preset voltage change is greater than the target bus voltage change.

[0165] It is understandable that during the process of the inverter circuit stopping operation, if the absolute value of the positive and negative bus voltage changes corresponding to at least one time group increases to be greater than or equal to the preset voltage change, the inverter circuit can be controlled to disconnect from the DC input unit and the power grid to avoid damage to the first film capacitor C1 or the second film capacitor C2 due to overvoltage, thereby reducing the possibility of power conversion device failure.

[0166] In one possible implementation, the method further includes: when the number of times the leakage current abnormality of the thin-film capacitor in the power conversion device is detected within a preset detection time reaches a target abnormality number, controlling the inverter circuit to operate in derating mode to reduce the output power of the inverter circuit. It is understood that when the power conversion device operates under harsh conditions such as high temperature and high humidity for a long time, the long-term self-healing accumulation of the thin-film capacitor may accelerate its aging and may also cause its capacitance to decay, leading to a decline in its performance. Therefore, the performance status of the thin-film capacitor can be predicted by the number of leakage current abnormalities. When the number of leakage current abnormalities reaches the target abnormality number, the inverter circuit can be controlled to operate in derating mode to avoid burning out the thin-film capacitor due to excessive leakage current. This can, to a certain extent, slow down the aging rate of the thin-film capacitor and prevent power conversion device failure caused by thin-film capacitor failure.

[0167] In one possible implementation, the method further includes: when the total number of times the leakage current abnormality of the thin-film capacitor in the photovoltaic power generation system is detected reaches a preset number of abnormalities, the power conversion device is controlled to stop working.

[0168] Specifically, when the total number of leakage current anomalies in the first and second film capacitors exceeds a preset number, it can be predicted that the safety performance of the first and second film capacitors is low. Therefore, the power conversion device can be stopped in advance to prevent film capacitor failure and avoid photovoltaic power generation system malfunctions caused by film capacitor failure. It is understandable that when the number of leakage current anomalies in the film capacitors reaches the limit value, the safety performance of the film capacitors is low, which may lead to film capacitor failure, resulting in the film capacitors burning out and potentially damaging other electronic components, causing the fault to spread. To avoid the above-mentioned failure situations, the power conversion device can be stopped in advance when the total number of leakage current anomalies in the film capacitors reaches the preset number, preventing damage to other electronic components and ensuring the safety of the power conversion device.

[0169] In summary, the positive and negative bus voltages exhibit different trends when the first or second film capacitor has an abnormal leakage current compared to when it does not, and the midpoint current also changes. Therefore, if the trends of the positive and negative bus voltages satisfy the trends when either the first or second film capacitor has an abnormal leakage current, and the absolute values ​​of the current change and the absolute values ​​of the positive and negative bus voltage changes meet certain conditions, then it can be determined that at least one film capacitor has an abnormal leakage current. It is evident that the trends of the positive and negative bus voltages, the absolute values ​​of the current change, and the changes in the positive and negative bus voltages can reflect the self-healing status of the film capacitors in real time, offering advantages such as high detection accuracy, high efficiency, and low cost. Furthermore, during the self-healing process of the film capacitors, if an abnormal leakage current is detected in any film capacitor, timely execution of protection strategies, such as transient blocking to stop the inverter circuit, can prevent excessive leakage current from causing film capacitor failure and consequently power conversion device malfunction, thus ensuring the stability of power generation from the power conversion device.

[0170] Please see Figure 7 , Figure 7 This is another schematic flowchart illustrating the leakage current detection method for a power conversion device provided in an embodiment of this application. The leakage current detection method for a power conversion device provided in an embodiment of this application is applicable to... Figures 2 to 5 The control unit in the corresponding specific implementation. This power conversion device can be used as follows: Figure 2 The photovoltaic power generation system shown is an example. Figure 2As shown, a photovoltaic power generation system may include a DC input unit and a power conversion device. The power conversion device may include a control unit, a positive DC bus BUS+, a negative DC bus BUS-, a first thin-film capacitor C1, a second thin-film capacitor C2, and an inverter circuit. The DC end of the photovoltaic power generation system may include a first output terminal dc1 and a second output terminal dc2 of the DC input unit. The first output terminal dc1 is connected to the positive DC bus BUS+, and the second output terminal dc2 is connected to the negative DC bus BUS-. The first thin-film capacitor C1 and the second thin-film capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The inverter circuit is connected between the positive DC bus BUS+ and the negative DC bus BUS-, and the series connection of the first thin-film capacitor C1 and the second thin-film capacitor C2 is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit can be connected to the power grid. The inverter circuit can convert the DC power provided by the DC input unit into AC power and output it to the power grid or load. Here, one end of the first film capacitor C1 is connected to the positive DC bus BUS+, and the other end of the first film capacitor C1 is connected to one end of the second film capacitor C2. The other end of the second film capacitor C2 is connected to the negative DC bus BUS-. The series connection terminal N of the first film capacitor C1 and the second film capacitor C2 is the connection point between the two film capacitors. This series connection terminal N can be the midpoint of the bus (referred to as the midpoint). The DC power provided by the DC input unit can be transmitted to the first film capacitor C1 and the second film capacitor C2 through the positive and negative DC buses (BUS+, BUS-), and stored through the first film capacitor C1 and the second film capacitor C2. The first film capacitor C1 and the second film capacitor C2 can also be used for midpoint balance control to make the capacitor voltage of the first film capacitor C1 equal to the capacitor voltage of the second film capacitor C2. (The last sentence appears to be incomplete and possibly refers to a specific configuration or feature.) Figures 3 to 5 In any power conversion device corresponding to the illustration, the leakage current detection method of the power conversion device provided in this application embodiment may include the following steps:

[0171] S201. Obtain the change in current flowing through the series connection of the first and second film capacitors between the first and second time points in each time group in at least one time group, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each time group in at least one time group, and process the change in current corresponding to each time group within the target detection time to obtain the change in current within the target detection time; the time interval between the first and second time points in any time group is an integer multiple of the fundamental period of the grid voltage.

[0172] In some feasible implementations, the current change corresponding to each time group can be the difference between the current value of the first current flowing through the series connection terminal at the first time point and the current value of the second current flowing through the series connection terminal at the second time point in each time group.

[0173] For example, if the first time point T1 of each time group is within [0, π / 3], then the second time point T2 of each time group can be [2kπ, π / 3 + 2kπ], where k is a positive integer. Here, the target detection time can be denoted as t0, and the time group within the target detection time can represent the sampling duration of the first time point T1 and the second time point T2 in each time group. Figure 3 For example, each time group within the target detection time can be represented by the first time point T1 in each time group being within [t1, t1+t0], where [t1, t1+t0] is the sampling interval for the first time point T1 in each time group, and the second time point T2 in each time group being within [t3, t3+t0], where [t3, t3+t0] is the sampling interval for the second time point T2 in each time group. Similarly, taking... Figure 4 For example, each time group within the target detection time can be represented as the first time point T1 in each time group being within [t1', t1'+t0], where [t1', t1'+t0] is the sampling interval of the first time point T1 in each time group, and the second time point T2 in each time group being within [t3', t3'+t0], where [t3', t3'+t0] is the sampling interval of the second time point T2 in each time group.

[0174] like Figure 3 As shown, the first film capacitor C1 did not exhibit leakage current abnormality at time t1, but did at time t3. The positive bus voltage at time t3 was lower than that at time t1, while the negative bus voltage at time t3 was higher than that at time t1. Taking the first and second time points in a time group as an example, where the first time point T1 is time t1 and the second time point T2 is time t3, the positive bus voltage in this time group decreases from time t1 through time t3, and the negative bus voltage increases from time t1 through time t3. However, when the first film capacitor C1 exhibits leakage current abnormality across multiple time groups, it's possible that the positive and negative bus voltages in a certain time group do not conform to the above trend. To reduce the false detection rate, the current changes corresponding to each time group can be processed to obtain the current changes within the target detection time. Thus, based on the current changes within the target detection time and the changes in the positive and negative bus voltages corresponding to each time group, it can be determined whether there is a leakage current abnormality in the film capacitor.

[0175] Similarly, such as Figure 4As shown, the second film capacitor C2 did not exhibit abnormal leakage current at time t1', but it did at time t3'. The positive bus voltage at time t3' decreased compared to the positive bus voltage at time t1', while the negative bus voltage at time t3' increased compared to the negative bus voltage at time t1'. Taking the first and second time points in a time group as an example, where the first time point T1 is time t1' and the second time point T2 is time t3', the positive bus voltage in this time group decreases from time t1' through time t3', while the negative bus voltage increases from time t1 through time t3. However, when the second film capacitor C2 exhibits abnormal leakage current in multiple time groups, it is possible that the positive and negative bus voltages in a certain time group do not meet the above-mentioned trend. In order to reduce the false detection rate, the current change corresponding to each time group can be processed to obtain the current change within the target detection time. In this way, the presence of abnormal leakage current of the film capacitor can be determined based on the current change within the target detection time and the positive and negative bus voltage changes corresponding to each time group.

[0176] For a detailed implementation of S201, please refer to the above. Figures 2 to 5 The implementation method executed by the control unit is not described in detail in the embodiments of this application.

[0177] S202. When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, output a detection result indicating that at least one of the first and second thin-film capacitors has an abnormal leakage current, and / or control the inverter circuit to stop working.

[0178] Understandably, the positive and negative bus voltages exhibit different trends when the first or second film capacitor has an abnormal leakage current compared to when it does not, and the midpoint current also changes; that is, both the current change and the changes in the positive and negative bus voltages change. Therefore, if the trends of the positive and negative bus voltages match those of the first or second film capacitor with an abnormal leakage current, the presence of an abnormal leakage current in the film capacitor can be determined based on the current change within the target detection time and the corresponding changes in the positive and negative bus voltages for each time group. This allows for timely and rapid detection of abnormal leakage currents and pinpointing the affected film capacitor. It also avoids inaccurate detection due to outliers or missing values, thus improving the accuracy of abnormal leakage current detection.

[0179] In one possible implementation, the above-mentioned processing based on the current change corresponding to each time group within the target detection time to obtain the current change within the target detection time includes: integrating the current change corresponding to each time group within the target detection time to obtain the current change within the target detection time. Here, since the first time point in each time group can be a continuous time point, and the second time point in each time group can also be a continuous time point, then each time group can also be a continuous time group, and the current change corresponding to each time group can also be continuous. Therefore, the current change corresponding to each time group within the target detection time can be integrated to obtain the current change within the target detection time. It is understood that if the current change corresponding to each time group is positive, the current change after integration will also be positive. If the current change corresponding to each time group is negative, the current change after integration will also be negative. Furthermore, because the abnormal current change corresponding to individual time groups has little impact on the result of integrating the current change corresponding to each time group within the target detection time. In summary, leakage current anomaly detection can be performed based on the changes in positive and negative bus voltages corresponding to each time group and the current changes within the target detection time obtained after integration processing. Furthermore, integrating the current changes corresponding to each time group improves data processing accuracy. The integrated current changes and positive and negative bus voltage changes more accurately reflect the self-healing status of the thin-film capacitor, thereby improving the accuracy of leakage current anomaly detection.

[0180] In one possible implementation, the detection result of abnormal leakage current of at least one of the first and second film capacitors is output as follows: when the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, when the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of abnormal leakage current of the first film capacitor is output.

[0181] It is understandable that if the current change corresponding to each time group is the difference between the midpoint current of the first film capacitor when leakage current anomaly occurs and the midpoint current of the first film capacitor when leakage current anomaly does not occur, then the current change corresponding to each time group is positive, and the current change after integration is also positive. If the current change corresponding to each time group is the difference between the midpoint current of the first film capacitor when leakage current anomaly does not occur and the midpoint current of the first film capacitor when leakage current anomaly occurs, then the current change corresponding to each time group is negative, and the current change within the target detection time after integration is also negative. The absolute values ​​of the positive and negative bus voltage changes corresponding to each time group are all greater than 0. In summary, leakage current anomaly detection of the first film capacitor can be performed based on the positive and negative bus voltage changes corresponding to each time group and the current change within the target detection time. By integrating the current changes corresponding to each time group, the accuracy of data processing can be further improved. Based on the current changes and positive and negative bus voltage changes after integration, the self-healing status of the thin film capacitor can be reflected more accurately, thereby improving the accuracy of detecting leakage current anomalies.

[0182] In one possible implementation, the detection result of abnormal leakage current of at least one of the first and second film capacitors is output as follows: when the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, and the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of abnormal leakage current of the second film capacitor is output.

[0183] It is understandable that if the current change corresponding to each time group is the difference between the midpoint current of the second film capacitor when leakage current anomaly occurs and the midpoint current of the second film capacitor when leakage current anomaly does not occur, then the current change corresponding to each time group is negative, and the current change within the target detection time after integration is also negative. If the current change corresponding to each time group is the difference between the midpoint current of the second film capacitor when leakage current anomaly does not occur and the midpoint current of the second film capacitor when leakage current anomaly occurs, then the current change corresponding to each time group is positive, and the current change after integration is also positive. The absolute values ​​of the positive and negative bus voltage changes corresponding to each time group are all greater than 0. By integrating the current changes corresponding to each time group, the data processing accuracy can be further improved. The current change and positive and negative bus voltage changes after integration can more accurately reflect the self-healing status of the film capacitor, thereby improving the accuracy of detecting leakage current anomalies.

[0184] In summary, when the first film capacitor does not exhibit leakage current abnormality, the voltage difference between the positive and negative bus voltages is zero because the positive and negative bus voltages are equal, and the midpoint current remains constant. When the first film capacitor exhibits leakage current abnormality, the positive bus voltage decreases compared to when it does not, while the negative bus voltage increases. Similarly, when the second film capacitor does not exhibit leakage current abnormality, the voltage difference between the positive and negative bus voltages is zero, and the midpoint current remains constant. However, when the first film capacitor exhibits leakage current abnormality, the positive bus voltage increases compared to when it does not, while the negative bus voltage decreases. Therefore, the changes in positive and negative bus voltages and current can reflect the changes in the positive and negative bus voltages and the midpoint current in real time, and thus indicate whether leakage current abnormality exists in the first or second film capacitor. It is evident that by analyzing the trends in positive and negative bus voltages, as well as the changes in both voltage and current, the self-healing status of the thin-film capacitor can be reflected in real time. This approach offers advantages such as high accuracy, high efficiency, and low cost. Furthermore, the changes in positive and negative bus voltages and current can effectively detect any abnormal leakage current during the self-healing process. Upon detecting abnormal leakage current, timely protection strategies, such as transient blocking, can be implemented to prevent excessive leakage current from causing capacitor failure and ultimately leading to photovoltaic system malfunctions, thus ensuring the stability of the photovoltaic power generation system.

Claims

1. A power conversion device, characterized in that, The power conversion device includes a control unit, a positive DC bus, a negative DC bus, a first thin-film capacitor, a second thin-film capacitor, and an inverter circuit. The first thin-film capacitor and the second thin-film capacitor are connected in series between the positive DC bus and the negative DC bus. The inverter circuit is connected between the positive DC bus and the negative DC bus, and the series connection terminal of the first thin-film capacitor and the second thin-film capacitor is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit is used to connect to the power grid. In at least one time group, if the positive bus voltage of each time group decreases from a first time point through a second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit is configured to output a detection result indicating abnormal leakage current in at least one of the first and second film capacitors when the absolute value of the change in current flowing through the series connection terminal of the first film capacitor and the second film capacitor is greater than or equal to a first change, and the absolute value of the change in positive and negative bus voltage between the first time point and the second time point in each time group is greater than or equal to the target bus voltage change, and / or control the inverter circuit to stop operating; the time interval between the first time point and the second time point in any time group is an integer multiple of the fundamental period of the grid voltage.

2. The power conversion device according to claim 1, characterized in that, When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit is further configured to output a detection result of abnormal leakage current in the first thin film capacitor when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change.

3. The power conversion device according to claim 1, characterized in that, When the positive bus voltage in each of the time groups increases from the first time point through the second time point, and the negative bus voltage in each of the time groups decreases from the first time point through the second time point, the control unit is further configured to output a detection result of abnormal leakage current in the second thin-film capacitor when the absolute value of the current change corresponding to each of the time groups is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each of the time groups is greater than or equal to the target bus voltage change.

4. The power conversion device according to claim 1, characterized in that, When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit is configured to output a detection result indicating abnormal leakage current in at least one of the first and second thin-film capacitors when the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, and / or control the inverter circuit to stop operating.

5. The power conversion device according to claim 4, characterized in that, When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit is further configured to output a detection result of abnormal leakage current in the first thin film capacitor when the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

6. The power conversion device according to claim 4, characterized in that, When the positive bus voltage in each of the time groups increases from the first time point through the second time point, and the negative bus voltage in each of the time groups decreases from the first time point through the second time point, the control unit is further configured to output a detection result indicating that the second thin-film capacitor has an abnormal leakage current when the absolute value of the current change corresponding to each of the time groups is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each of the time groups is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period.

7. The power conversion device according to any one of claims 1 to 6, characterized in that, The inverter circuit is connected to the DC input unit via a DC disconnectable switch, and the inverter circuit is connected to the power grid via a grid-connected relay; During the process of the inverter circuit stopping operation, the control unit is further configured to control the DC disconnectable switch and the grid-connected relay to disconnect when the absolute value of the positive and negative bus voltage changes corresponding to at least one of the time groups increases to be greater than or equal to a preset voltage change, so as to control the inverter circuit to disconnect from the DC input unit and the power grid; the preset voltage change is greater than the target bus voltage change.

8. The power conversion device according to any one of claims 1 to 6, characterized in that, The control unit is also configured to control the inverter circuit to operate in derating mode to reduce the output power of the inverter circuit when the number of times the leakage current abnormality of the thin film capacitor in the power conversion device is detected to reach the target abnormality number within a preset detection time.

9. The power conversion device according to any one of claims 1 to 6, characterized in that, The control unit is also configured to control the power conversion device to stop working when the total number of times an abnormal leakage current of a thin-film capacitor in the power conversion device is detected reaches a preset number of abnormalities.

10. A power conversion device, characterized in that, The power conversion device includes a control unit, a positive DC bus, a negative DC bus, a first thin-film capacitor, a second thin-film capacitor, and an inverter circuit. The first thin-film capacitor and the second thin-film capacitor are connected in series between the positive DC bus and the negative DC bus. The inverter circuit is connected between the positive DC bus and the negative DC bus, and the series connection terminal of the first thin-film capacitor and the second thin-film capacitor is connected to the input terminal of the inverter circuit. The output terminal of the inverter circuit is used to connect to the power grid. In at least one time group, if the positive bus voltage of each time group decreases from a first time point through a second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or if the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, the control unit is configured to determine the current flowing through the series connection of the first thin-film capacitor and the second thin-film capacitor between the first time point and the second time point in each time group within the target detection time. The change is processed to obtain the current change within the target detection time. When the absolute value of the current change within the target detection time is greater than or equal to the second change, and the absolute value of the positive and negative bus voltage changes between the first time point and the second time point in each time group is greater than or equal to the target bus voltage change, a detection result indicating that at least one of the first and second film capacitors has abnormal leakage current is output, and / or the inverter circuit is controlled to stop working; the time interval between the first time point and the second time point in any time group is an integer multiple of the fundamental period of the grid voltage.

11. The power conversion device according to claim 10, wherein the control unit is further configured to perform integral processing on the current change amount corresponding to each time group within the target detection time to obtain the current change amount within the target detection time.

12. The power conversion device according to claim 11, characterized in that, When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, the control unit is further configured to output a detection result indicating that the first thin-film capacitor has an abnormal leakage current when the absolute value of the change within the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage.

13. The power conversion device according to claim 11, characterized in that, When the positive bus voltage in each of the time groups increases from the first time point through the second time point, and the negative bus voltage in each of the time groups decreases from the first time point through the second time point, the control unit is further configured to output a detection result indicating abnormal leakage current in the second thin-film capacitor when the absolute value of the change within the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each of the time groups is greater than or equal to the change in the target bus voltage.

14. A method for detecting leakage current in a power conversion device, the method being applied to the power conversion device, the power conversion device comprising a control unit, a positive DC bus, a negative DC bus, a first thin-film capacitor, a second thin-film capacitor, and an inverter circuit, wherein the first thin-film capacitor and the second thin-film capacitor are connected in series between the positive DC bus and the negative DC bus, the inverter circuit is connected between the positive DC bus and the negative DC bus, and the series connection terminal of the first thin-film capacitor and the second thin-film capacitor is connected to the input terminal of the inverter circuit, the output terminal of the inverter circuit being used to connect to the power grid, the method comprising: Obtain the absolute value of the change in current flowing through the series connection of the first thin-film capacitor and the second thin-film capacitor between a first time point and a second time point in each of at least one time group, and the absolute value of the change in positive and negative bus voltage between the first time point and the second time point in each of at least one time group; the time interval between the first time point and the second time point in any time group is an integer multiple of the fundamental period of the grid voltage; When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, output a detection result indicating that at least one of the first and second film capacitors has an abnormal leakage current, and / or control the inverter circuit to stop working.

15. The method according to claim 14, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the detection result of the first thin film capacitor having abnormal leakage current is output.

16. The method according to claim 14, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the detection result of leakage current abnormality in the second thin film capacitor is output.

17. The method according to claim 14, characterized in that, The method further includes: When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result indicating that at least one of the first and second thin-film capacitors has abnormal leakage current is output, and / or the inverter circuit is controlled to stop working.

18. The method according to claim 16, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of the first thin film capacitor having abnormal leakage current is output.

19. The method according to claim 17, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group is greater than or equal to the first change, the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, and the target detection time is greater than the fundamental period, the detection result of the second thin film capacitor having abnormal leakage current is output.

20. The method according to any one of claims 14 to 19, characterized in that, The inverter circuit is connected to the DC input unit via a DC disconnectable switch, and the inverter circuit is connected to the power grid via a grid-connected relay. The method further includes: During the process of the inverter circuit stopping operation, when the absolute value of the positive and negative bus voltage changes corresponding to at least one of the time groups increases to be greater than or equal to a preset voltage change, the DC disconnectable switch and the grid-connected relay are controlled to disconnect the inverter circuit from the DC input unit and the power grid; the preset voltage change is greater than the target bus voltage change.

21. The method according to any one of claims 14 to 19, characterized in that, The method further includes: When the number of times the leakage current abnormality of the thin film capacitor in the power conversion device is detected within the preset detection time reaches the target abnormality number, the inverter circuit is controlled to operate in derating mode to reduce the output power of the inverter circuit.

22. The method according to any one of claims 14 to 19, characterized in that, The method further includes: When the total number of times that leakage current abnormality of the thin film capacitor in the power conversion device is detected reaches a preset number of abnormalities, the power conversion device is controlled to stop working.

23. A method for detecting leakage current in a power conversion device, the method being applied to the power conversion device, the power conversion device comprising a control unit, a positive DC bus, a negative DC bus, a first thin-film capacitor, a second thin-film capacitor, and an inverter circuit, wherein the first thin-film capacitor and the second thin-film capacitor are connected in series between the positive DC bus and the negative DC bus, the inverter circuit is connected between the positive DC bus and the negative DC bus, and the series connection terminal of the first thin-film capacitor and the second thin-film capacitor is connected to the input terminal of the inverter circuit, the output terminal of the inverter circuit being used to connect to the power grid, the method comprising: The method acquires the change in current flowing through the series connection of the first and second film capacitors between a first time point and a second time point in each of at least one time group, and the absolute value of the change in positive and negative bus voltage between the first and second time points in each of at least one time group. The method then processes the current change based on the current change corresponding to each of the time groups within a target detection time to obtain the current change within the target detection time. The time interval between the first and second time points in any one of the time groups is an integer multiple of the fundamental period of the grid voltage. When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, or when the positive bus voltage of each time group increases from the first time point through the second time point, and the negative bus voltage of each time group decreases from the first time point through the second time point, if the absolute value of the current change corresponding to each time group within the target detection time is greater than or equal to the first change, and the absolute value of the positive and negative bus voltage changes corresponding to each time group is greater than or equal to the target bus voltage change, the detection result indicating abnormal leakage current of at least one of the first and second film capacitors is output, and / or the inverter circuit is controlled to stop working.

24. The method according to claim 23, wherein processing based on the current change amount corresponding to each time group within the target detection time to obtain the current change amount within the target detection time includes: The current change corresponding to each time group within the target detection time is integrated to obtain the current change within the target detection time.

25. The method according to claim 24, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage of each time group decreases from the first time point through the second time point, and the negative bus voltage of each time group increases from the first time point through the second time point, when the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of the first thin film capacitor having abnormal leakage current is output.

26. The method according to claim 24, characterized in that, The detection result of abnormal leakage current in at least one of the first and second film capacitors includes: When the positive bus voltage in each time group increases from the first time point through the second time point, and the negative bus voltage in each time group decreases from the first time point through the second time point, if the absolute value of the change in the target detection time is greater than or equal to the second change, and the absolute value of the change in the positive and negative bus voltages corresponding to each time group is greater than or equal to the change in the target bus voltage, the detection result of abnormal leakage current in the second thin film capacitor is output.

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