Disconnection detection device and disconnection detection method

Abstract

Provided is a disconnection detection device (10) comprising: a measurement circuit (12) that is connected to at least one cable of a pair of cables (6a, 6b) between a solar panel (3) and a power conversion device (4) and that inputs a measurement signal into the at least one cable when the power conversion device (4) is stopped, thereby measuring measurement data relating to disconnection of the pair of cables (6a, 6b) at each optional timing; a storage unit (14) that stores a determination value based on measurement data measured by the measurement circuit (12); and a detection unit (16) that compares the determination value with the measurement data measured by the measurement circuit (12) after the storage unit (14) has stored the determination value and that detects, if the measurement data has changed by a prescribed amount or greater with respect to the determination value, a disconnection of the pair of cables (6a, 6b) and outputs an alarm signal. As a result, a disconnection detection device and a disconnection detection method that can be used to more easily set a determination value can be provided.

Description

Wire break detection device and wire break detection method

[0001] FIELD Embodiments of the present invention relate to a wire break detection device and a wire break detection method.

[0002] There is a photovoltaic power generation system that includes a solar panel and a power converter. The power converter is connected to the solar panel via a pair of cables and to an AC power grid, converts DC power output from the solar panel into AC power that conforms to the grid, and supplies the converted AC power to the grid.

[0003] Cable theft has become a problem in these solar power generation systems. Solar panels stop generating electricity at night. The cables connecting the solar panels and the power conversion equipment do not receive a large amount of power when power generation is stopped at night. For this reason, thefts have occurred in which the cables between the solar panels and the power conversion equipment, which have a low risk of electric shock, are cut and stolen. Such thefts are on the rise due to the increase in solar power generation systems and the rising prices of the metal materials used in the cables.

[0004] To prevent such theft, it has been proposed to use a cable breakage detection device in a solar power generation system that detects cable breakage and outputs an alarm in response to the detection.The cable breakage detection device detects cable breakage by, for example, measuring a change in capacitance between the cable (solar panel) and the ground, or a change in the reflected wave from the cable when a pulsed measurement signal is input to the cable.

[0005] As described above, when measuring changes in capacitance or reflected waves, it is necessary to set a judgment value (threshold value) for detecting a disconnection for the measurement results. However, the setting of the judgment value differs depending on the configuration of the solar power generation system, such as the number of solar panels and the length of the cable. Therefore, the judgment value needs to be set for each solar power generation system.

[0006] Furthermore, the configuration of a photovoltaic power generation system may change during operation. For example, if multiple photovoltaic panels are connected to a power conversion device, the number of photovoltaic panels connected to the power conversion device may change due to a failure of one of the photovoltaic panels. If the determination value is left unchanged when the configuration of the photovoltaic power generation system changes, there is a concern that the disconnection detection device may erroneously detect a cable disconnection. Therefore, whenever the configuration of the photovoltaic power generation system changes, it becomes necessary to reset the determination value.

[0007] As described above, the setting of the judgment value needs to be performed each time a photovoltaic power generation system is installed and each time the configuration is changed, which is time-consuming for the administrator of the photovoltaic power generation system, etc. For this reason, it is desirable to make it possible to set the judgment value more easily in a wire break detection device used in a photovoltaic power generation system.

[0008] Patent No. 6550001 Patent No. 6550002 Patent No. 6642730 JP 2022-158111 A

[0009] The embodiments of the present invention provide a wire breakage detection device and a wire breakage detection method that allow for easier setting of a judgment value.

[0010] According to an embodiment of the present invention, there is provided a wire break detection device for use in a solar power generation system including a solar panel, and a power conversion device connected to the solar panel via a pair of cables and connected to an AC power grid, converting DC power output from the solar panel into AC power according to the power grid, and supplying the converted AC power to the power grid. The wire break detection device includes: a measurement circuit connected to at least one of the pair of cables, and measuring measurement data related to a wire break in the pair of cables at any timing by inputting a measurement signal to the at least one cable when the power conversion device is stopped; a memory unit that stores a judgment value based on the measurement data measured by the measurement circuit; and a detection unit that compares the measurement data measured by the measurement circuit with the judgment value after the memory unit has stored the judgment value, and detects a wire break in the pair of cables if the measurement data changes by a predetermined amount relative to the judgment value and outputs an alarm signal.

[0011] According to the embodiments of the present invention, a disconnection detection device and a disconnection detection method are provided that allow for easier setting of a judgment value.

[0012] Fig. 1 is a block diagram schematically showing a solar power generation system and a wire-break detection device according to an embodiment; Fig. 2 is a flowchart schematically showing an example of the operation of the wire-break detection device according to an embodiment; Fig. 3 is a block diagram schematically showing a modified example of the solar power generation system and the wire-break detection device according to an embodiment; Fig. 4 is a block diagram schematically showing a modified example of the solar power generation system and the wire-break detection device according to an embodiment; Fig. 5 is a block diagram schematically showing a modified example of the solar power generation system and the wire-break detection device according to an embodiment;

[0013] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc., are not necessarily the same as those in reality. Even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In this specification and each drawing, elements similar to those previously described with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0014] Fig. 1 is a block diagram schematically illustrating a solar power generation system and a line break detection device according to an embodiment. As illustrated in Fig. 1, a solar power generation system 2 includes a solar panel 3, a power conversion device 4, and a line break detection device 10. The solar power generation system 2 includes, for example, a plurality of solar panels 3 and further includes a current collection box 5. The current collection box 5 aggregates the outputs of the plurality of solar panels 3 by connecting the plurality of solar panels 3 in series, parallel, or series-parallel.

[0015] The power conversion device 4 is connected to the solar panel 3 via a pair of cables 6a, 6b. The power conversion device 4 is connected to a plurality of solar panels 3, for example, via the pair of cables 6a, 6b and a current collection box 5. As a result, the power conversion device 4 receives input of DC power output from the plurality of solar panels 3. The cable 6a is, for example, a cable on the high potential side of the DC power output from the plurality of solar panels 3. The cable 6b is, for example, a cable on the low potential side of the DC power output from the plurality of solar panels 3.

[0016] However, the number of solar panels 3 provided in the solar power generation system 2 may be one. The power conversion device 4 may be connected to one solar panel 3 via a pair of cables 6a, 6b and receive input of DC power output from one solar panel 3. The solar power generation system 2 may have any configuration that has at least one solar panel 3 and can supply DC power output from the at least one solar panel 3 to the power conversion device 4. The current collection box 5 is provided as needed and can be omitted.

[0017] The power conversion device 4 is connected to the solar panel 3 via a pair of cables 6a, 6b, and also connected to the AC power grid PS. The power conversion device 4 converts the DC power output from the solar panel 3 into AC power that conforms to the power grid PS, and supplies the converted AC power to the power grid PS. The power conversion device 4 may supply the converted AC power to the power grid PS, or may supply it to a load connected to the power grid PS. In other words, the solar power generation system 2 may be a system that performs reverse power flow (selling power) to the power grid PS, or may be a self-consumption system.

[0018] The power conversion device 4 includes, for example, a converter 4a, a control unit 4b, and a housing 4c. The converter 4a is connected to the solar panel 3 via a pair of cables 6a, 6b, and is also connected to an AC power grid PS. The converter 4a is connected to the power grid PS via, for example, a transformer, a switch, etc. (not shown). The power conversion device 4 may further include a transformer, a switch, etc. The converter 4a converts DC power output from the solar panel 3 into AC power according to the power grid PS, and supplies the converted AC power to the power grid PS.

[0019] The control unit 4b is connected to the converter 4a and controls the power conversion operation of the converter 4a. The control unit 4b communicates with, for example, a higher-level controller (not shown) and controls the operation of the converter 4a based on commands from the higher-level controller.

[0020] The housing 4c accommodates the converter 4a and the control unit 4b inside. The housing 4c (power conversion device 4) is installed outdoors, for example, together with the solar panel 3. The housing 4c protects the converter 4a and the control unit 4b from rain, dust, and the like when installed outdoors. The housing 4c is sometimes called, for example, an enclosure. However, the power conversion device 4 is not limited to being installed outdoors, and may be installed indoors, such as in a dedicated building. When the power conversion device 4 is installed indoors, the housing 4c may be omitted.

[0021] The wire break detection device 10 is used in the solar power generation system 2 and detects a break in the pair of cables 6 a, 6 b between the solar panel 3 and the power conversion device 4. In this way, the wire break detection device 10 can prevent the pair of cables 6 a, 6 b, which pose a low risk of electric shock, from being cut and taken away, for example, at night when the solar panel 3 stops generating power. In other words, the wire break detection device 10 is a theft prevention device for preventing the theft of the pair of cables 6 a, 6 b.

[0022] The disconnection detection device 10 is provided, for example, in the housing 4c together with the converter 4a and the control unit 4b. This protects the disconnection detection device 10 from rain, dust, and the like. It also prevents the disconnection detection device 10 from being damaged by, for example, someone trying to remove the cables 6a, 6b. However, the disconnection detection device 10 may also be installed outside the housing 4c. For example, the disconnection detection device 10 may be located near the cables 6a, 6b, separate from the power conversion device 4. The location where the disconnection detection device 10 is installed is not limited to the above, and may be any location where disconnection detection of the cables 6a, 6b can be properly detected.

[0023] The disconnection detection device 10 includes a measurement circuit 12, a storage unit 14, and a detection unit 16. The measurement circuit 12 is connected to at least one of the pair of cables 6 a, 6 b, and when the power conversion device 4 is stopped, the measurement circuit 12 inputs a measurement signal to at least one of the cables, thereby measuring measurement data related to a disconnection of the pair of cables 6 a, 6 b at any desired timing.

[0024] More specifically, the time when the power conversion device 4 is stopped refers to the time when the power conversion operation by the converter 4a is stopped. In other words, the time when the supply of AC power from the converter 4a to the power grid PS is stopped. The measurement circuit 12 measures the measurement data when the power generated by the solar panel 3 is reduced and the operation of the power conversion device 4 (converter 4a) is stopped, for example, at night.

[0025] The measurement circuit 12 is connected to, for example, the control unit 4b, and determines whether the power conversion device 4 (converter 4a) is stopped by receiving a stop signal from the control unit 4b indicating that the power conversion device 4 (converter 4a) is stopped. The measurement circuit 12 also receives, for example, an operation signal from the control unit 4b indicating the operation of the power conversion device 4 (converter 4a). For example, the measurement circuit 12 measures measurement data when receiving a stop signal from the control unit 4b, and stops measuring the measurement data when receiving an operation signal from the control unit 4b.

[0026] However, the method for determining whether the power conversion device 4 has stopped is not limited to the above. For example, the measurement circuit 12 may be connected to each of the pair of cables 6 a, 6 b, and whether the power conversion device 4 has stopped may be determined based on the magnitude of the DC power supplied from the solar panel 3 to the power conversion device 4. The measurement circuit 12 may determine that the power conversion device 4 has stopped when the magnitude of the DC voltage is equal to or lower than a predetermined value, for example.

[0027] For example, the measurement circuit 12 may be connected to the AC side of the power conversion device 4, and it may be determined whether the power conversion device 4 has stopped based on the magnitude of the AC power output from the power conversion device 4. The measurement circuit 12 may determine that the power conversion device 4 has stopped when, for example, the magnitude of the AC power is equal to or less than a predetermined value.

[0028] The method for determining whether the power conversion device 4 has stopped is not limited to the above, and any method that allows the measurement circuit 12 to appropriately determine whether the power conversion device 4 has stopped may be used.

[0029] In this example, the measurement circuit 12 is connected to each of the pair of cables 6 a and 6 b. The measurement circuit 12, for example, inputs a pulsed measurement signal between the pair of cables 6 a and 6 b and measures the reflected wave of the measurement signal from the pair of cables 6 a and 6 b as measurement data.

[0030] The measurement circuit 12 performs measurements at regular intervals, for example, when the power conversion device 4 is stopped. In other words, the measurement circuit 12 performs measurements periodically when the power conversion device 4 is stopped. However, the measurements by the measurement circuit 12 do not necessarily have to be performed at regular intervals. The measurement intervals of the measurement circuit 12 may be changed based on, for example, a predetermined setting. The measurement intervals of the measurement circuit 12 may be any interval that allows the measurement circuit 12 to repeatedly perform measurements when the power conversion device 4 is stopped.

[0031] The memory unit 14 stores a judgment value based on the measurement data measured by the measurement circuit 12. As described above, when the measurement circuit 12 measures a reflected wave as measurement data, the memory unit 14 stores, as judgment values, for example, the magnitude (amplitude) of the reflected wave and the reflection time from the input of the measurement signal to the measurement of the reflected wave.

[0032] The storage unit 14 stores, for example, a judgment value based on the initial measurement data. More specifically, the initial measurement data is measurement data measured for the first time by the measurement circuit 12 when the disconnection detection device 10 is introduced into the solar power generation system 2 and operated for the first time. The storage unit 14 stores, for example, the magnitude and reflection time of the reflected wave based on the initial measurement data as the judgment value.

[0033] The storage unit 14 may store, for example, a judgment value based on the average value of multiple pieces of measurement data acquired by several measurements by the measurement circuit 12. The storage unit 14 stores, for example, a judgment value based on the average value of multiple pieces of measurement data acquired by several consecutive measurements starting from the first measurement. The storage unit 14 stores, for example, the average value of the magnitude of the reflected wave of the multiple pieces of measurement data and the average value of the reflection time of the multiple pieces of measurement data as the judgment value.

[0034] In this way, when the judgment value is set based on the average value of multiple measurement data, the influence of measurement defects and the like can be suppressed and the judgment value can be set more appropriately than when the judgment value is set based on a single measurement data. However, the method for setting the judgment value is not limited to the above, and any method that can appropriately set the judgment value based on measurement data can be used.

[0035] Furthermore, the storage unit 14 resets the judgment value each time the operation of the power conversion device 4 stops, based on the initial measurement data measured by the measurement circuit 12 after the power conversion device 4 stops the supply of AC power to the power grid PS. In this case as well, the storage unit 14 may reset the judgment value each time the operation of the power conversion device 4 stops, based on the average value of multiple measurement data obtained by several consecutive measurements taken by the measurement circuit 12 from the initial measurement after the power conversion device 4 stops the supply of AC power to the power grid PS.

[0036] The detection unit 16 compares the measurement data measured by the measurement circuit 12 with the judgment value after the memory unit 14 has stored the judgment value, and detects a break in the pair of cables 6a, 6b if the measurement data changes by a predetermined amount or more relative to the judgment value.

[0037] When the measurement circuit 12 measures the reflected waves as measurement data, if the pair of cables 6 a, 6 b is broken, changes occur such as a decrease in the magnitude of the reflected waves (the reflected waves disappear) or a shortening or lengthening of the reflection time of the reflected waves. Therefore, the detection unit 16 detects a break in the pair of cables 6 a, 6 b, for example, when at least one of the magnitude and reflection time of the reflected waves changes by a predetermined amount or more.

[0038] When the detector 16 detects a break in the pair of cables 6a, 6b, it outputs an alarm signal in response to the detection of the break.

[0039] The disconnection detection device 10 further includes an alarm 18 that outputs at least one of light and sound as an alarm. The alarm 18 is disposed, for example, near the pair of cables 6a, 6b.

[0040] The detection unit 16 is connected to, for example, an alarm device 18, and outputs an alarm signal to the alarm device 18, thereby causing the alarm device 18 to issue an alarm when a disconnection of the pair of cables 6 a, 6 b is detected. Note that the alarm device 18 may be provided in the solar power generation system 2, for example, separately from the disconnection detection device 10. The disconnection detection device 10 does not necessarily have to include the alarm device 18.

[0041] 2 is a flowchart showing an example of the operation of the disconnection detection device according to the embodiment. When a solar power generation system 2 is newly installed or when the disconnection detection device 10 is newly installed in an existing solar power generation system 2, the wiring of each part is performed as shown in FIG. 1, and then the power conversion device 4 is stopped and the disconnection detection device 10 is operated.

[0042] When the measurement circuit 12 starts operation with the power conversion device 4 stopped, the measurement circuit 12 starts measuring the measurement data (step S101 in FIG. 2). After starting to measure the measurement data, the measurement circuit 12 measures the measurement data at any timing. For example, the measurement circuit 12 measures the measurement data periodically.

[0043] The storage unit 14 stores a judgment value based on the initial measurement data measured by the measurement circuit 12 (step S102 in FIG. 2).

[0044] In this way, in the disconnection detection device 10, the judgment value is automatically stored in the storage unit 14 based on the measurement data when the pair of cables 6 a, 6 b are connected. This makes it possible to appropriately set the judgment value according to the configuration of the solar power generation system 2. Therefore, even when a solar power generation system 2 or a disconnection detection device 10 is newly installed, for example, the administrator of the solar power generation system 2 does not need to set the judgment value, which reduces the workload of the administrator of the solar power generation system 2.

[0045] As mentioned above, the judgment value may be set based on the average value of multiple measurement data obtained by several measurements by the measurement circuit 12. In this case, the influence of a measurement error in a single measurement can be suppressed, and the judgment value can be set more appropriately.

[0046] After the judgment value is stored in the memory unit 14, the detection unit 16 detects a break in the pair of cables 6a, 6b each time a measurement is performed by the measurement circuit 12 (step S103 in FIG. 2). As described above, the detection unit 16 compares the measurement data measured by the measurement circuit 12 after the memory unit 14 stores the judgment value with the judgment value, and detects a break in the pair of cables 6a, 6b when the measurement data has changed by a predetermined amount or more compared to the judgment value.

[0047] When the detector 16 detects a break in the pair of cables 6a, 6b, it outputs an alarm signal in response to the detection of the break (step S104 in FIG. 2).

[0048] The detection unit 16 outputs an alarm signal to the alarm device 18, for example, to cause the alarm device 18 to issue an alarm. This makes it possible to notify, for example, a manager of the solar power generation system 2 that a disconnection has occurred in the pair of cables 6a, 6b. In addition, for example, an alarm can be issued to anyone attempting to steal the cables 6a, 6b, thereby preventing theft of the pair of cables 6a, 6b.

[0049] If the detector 16 does not detect a disconnection in the pair of cables 6 a, 6 b, the measuring circuit 12 determines whether the power converter 4 has started operating (step S105 in FIG. 2 ). The measuring circuit 12 determines whether the power converter 4 has started operating, for example, based on whether an operation signal has been input from the controller 4 b.

[0050] If the measurement circuit 12 determines that the power conversion device 4 has not started operating, it continues to measure the measurement data at any timing. In this case, the process returns to step S103, and the detection unit 16 detects a break in the pair of cables 6 a, 6 b every time the measurement circuit 12 performs a measurement.

[0051] On the other hand, when the measurement circuit 12 determines that the power conversion device 4 has started operating, it stops measuring the measurement data (step S106 in FIG. 2 ). In other words, when the power conversion device 4 starts operating, the disconnection detection device 10 stops operating. If the pair of cables 6 a, 6 b is disconnected while the power conversion device 4 is operating, the input of DC power is suddenly interrupted, so that the power conversion device 4 can detect the disconnection of the pair of cables 6 a, 6 b even if the disconnection detection device 10 has stopped operating.

[0052] After stopping the measurement of the measurement data, the measurement circuit 12 determines whether the power electronics device 4 has stopped (step S107 in FIG. 2). The measurement circuit 12 determines whether the power electronics device 4 has stopped, for example, based on whether a stop signal has been input from the control unit 4 b.

[0053] In response to determining that the power conversion device 4 has stopped, the measurement circuit 12 resumes measuring the measurement data at each arbitrary timing (step S108 in FIG. 2).

[0054] The memory unit 14 resets the judgment value each time the operation of the power conversion device 4 stops, based on the initial measurement data measured by the measurement circuit 12 after the power conversion device 4 stops supplying AC power to the power grid PS (step S109 in Figure 2).

[0055] For example, during operation of the power conversion device 4, some of the solar panels 3 may fail, changing the number of solar panels 3 connected to the power conversion device 4, and the configuration of the solar power generation system 2 may change during operation of the power conversion device 4. If the determination value is left unchanged when the configuration of the solar power generation system 2 changes in this way, the detection unit 16 may erroneously detect a disconnection of the cables 6 a, 6 b.

[0056] As described above, by resetting the judgment value each time the operation of the power conversion device 4 is stopped, it is possible to prevent the detection unit 16 from falsely detecting a break in the cables 6a and 6b, even if the configuration of the solar power generation system 2 changes while the power conversion device 4 is operating.

[0057] After the memory unit 14 resets the judgment value, the processing returns to step S103, and each time a measurement is performed by the measurement circuit 12, the detection unit 16 detects a break in the pair of cables 6a, 6b based on the reset judgment value.

[0058] As described above, in the wire break detection device 10 according to this embodiment, the judgment value is automatically stored in the storage unit 14 based on the measurement data when the pair of cables 6 a, 6 b are connected. Therefore, in the wire break detection device 10 according to this embodiment, the judgment value can be set more easily. For example, even when a solar power generation system 2 or a wire break detection device 10 is newly installed, it is possible to reduce the time and effort required for the administrator of the solar power generation system 2 to set the judgment value.

[0059] Furthermore, in the disconnection detection device 10 according to the present embodiment, the storage unit 14 resets the judgment value each time the operation of the power conversion device 4 stops, based on the initial measurement data measured by the measurement circuit 12 after the power conversion device 4 stops supplying AC power to the power grid PS. This prevents the administrator of the photovoltaic power generation system 2 from having to reset the judgment value, even when the configuration of the photovoltaic power generation system 2 changes while the power conversion device 4 is in operation, for example. This further reduces the workload of the administrator of the photovoltaic power generation system 2 and provides a more convenient disconnection detection device 10.

[0060] 3 is a block diagram schematically illustrating a modified example of a solar power generation system and a wire breakage detection device according to the embodiment. As shown in FIG. 3, in a solar power generation system 2a, a wire breakage detection device 10a further includes a ground terminal 20. Note that components that are substantially the same in function and configuration as those in the above embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0061] The ground terminal 20 is set to a ground potential. For example, the ground terminal 20 is set to a ground potential by being connected to a ground electrode buried in the ground. However, the configuration of the ground terminal 20 is not limited to this, and any configuration that can be set to a ground potential may be used.

[0062] In the disconnection detection device 10a, the measurement circuit 12a is connected to one cable 6b of the pair of cables 6a, 6b and also to the ground terminal 20. The measurement circuit 12a is not limited to being connected to the low-potential cable 6b, but may also be connected to the high-potential cable 6a. For example, a diode for preventing backflow may be provided in one of the cables 6a, 6b. In this case, the measurement circuit 12a is connected to the cable 6a, 6b that is not provided with the diode.

[0063] The measurement circuit 12a measures, as measurement data, the magnitude of the capacitance between one cable 6b of the pair of cables 6a, 6b and the ground terminal 20. The measurement circuit 12a inputs an AC signal (AC voltage) as a measurement signal between the cable 6b and the ground terminal 20. The measurement circuit 12a measures the current flowing between the cable 6b and the ground terminal 20 when the AC signal is input, and the voltage between the cable 6b and the ground terminal 20 when the AC signal is input, and calculates the impedance between the cable 6b and the ground terminal 20 based on the measured current and voltage. The measurement circuit 12a then calculates the magnitude of the capacitance between the cable 6b and the ground terminal 20 from the calculated impedance.

[0064] This allows the measurement circuit 12a to measure, as measurement data, the magnitude of the capacitance between the cable 6b and the ground terminal 20. However, the method for measuring the magnitude of the capacitance by the measurement circuit 12a is not limited to the above, and any method that can appropriately measure the magnitude of the capacitance between one of the pair of cables 6a, 6b and the ground terminal 20 may be used.

[0065] In the disconnection detection device 10a, the memory unit 14 stores the magnitude of the capacitance measured by the measurement circuit 12a as a judgment value. For example, the memory unit 14 may store the average value of the magnitude of the capacitance of a plurality of measurement data as the judgment value.

[0066] When the measurement circuit 12a measures the magnitude of capacitance as measurement data, if one of the pair of cables 6a, 6b is broken, the magnitude of the capacitance between one of the pair of cables 6a, 6b and the ground terminal 20 decreases. Therefore, in the breakage detection device 10a, the detection unit 16 detects a break in the pair of cables 6a, 6b when the magnitude of the capacitance of the measurement data becomes smaller than the determination value by a predetermined amount or more.

[0067] In this way, the measurement circuit 12a may measure, as measurement data, the magnitude of the capacitance between one of the pair of cables 6a, 6b and the ground terminal 20. In this case, too, it is possible to appropriately detect a disconnection in the pair of cables 6a, 6b, as in the above embodiment.

[0068] The measurement circuit 12a may measure, for example, the magnitude of the reflected wave and the capacitance as measurement data, thereby more appropriately detecting a break in the pair of cables 6a, 6b.

[0069] However, the configuration of the measurement circuit 12a is not limited to the above, and may be any configuration that is connected to at least one of the pair of cables 6a, 6b, and that can appropriately measure measurement data related to a break in the pair of cables 6a, 6b by inputting a measurement signal to at least one of the cables when the power conversion device 4 is stopped.

[0070] 4 is a block diagram schematically illustrating a modified example of a solar power generation system and a wire break detection device according to the embodiment. As illustrated in FIG. 4, in a solar power generation system 2b, a detector 16 of a wire break detection device 10b communicates with an external device 30, and outputs an alarm signal to the external device 30 when a wire break in a pair of cables 6a, 6b is detected. The communication between the detector 16 and the external device 30 may be wired or wireless.

[0071] The external device 30 is, for example, a terminal of a manager of the solar power generation system 2b. The manager's terminal may be a personal computer installed in a room or a mobile terminal such as a smartphone owned by the manager. The external device 30 may be, for example, a terminal of a security company entrusted with security for the solar power generation system 2b.

[0072] In this way, the detection unit 16 may output an alarm signal to the external device 30. In this case, the disconnection of the pair of cables 6a, 6b can be appropriately notified to a manager or security officer of the photovoltaic power generation system 2b. For example, by sending a manager or security officer to the site, the theft of the pair of cables 6a, 6b can be prevented.

[0073] The detection unit 16 may, for example, output an alarm signal to each of the alarm device 18 and the external device 30. This makes it possible to appropriately notify, for example, a manager or security officer of a break in the pair of cables 6 a, 6 b, and to issue an alarm to anyone attempting to take away the cables 6 a, 6 b.

[0074] The detection unit 16 may output an alarm signal to, for example, the control unit 4b of the power conversion device 4. In this case, for example, before the power conversion device 4 starts operating, the control unit 4b can be notified of the occurrence of an abnormality in the cables 6a, 6b. Also, for example, the alarm signal can be output to an external device 30 or a higher-level controller via the control unit 4b. However, the output destination of the alarm signal is not limited to the above. The output destination of the alarm signal may be any device that needs to output an alarm signal.

[0075] 5 is a block diagram illustrating a modified example of the solar power generation system and the disconnection detection device according to the embodiment. As illustrated in FIG. 5, in the solar power generation system 2c, the disconnection detection device 10c is provided in the control unit 4b of the power conversion device 4.

[0076] In this way, the disconnection detection device 10c is not limited to being provided separately from the power conversion device 4, but may be provided in the control unit 4b of the power conversion device 4. In other words, the power conversion device 4 may include the measurement circuit 12, the memory unit 14, and the detection unit 16, and may detect a disconnection in the pair of cables 6a, 6b.

[0077] In this case, for example, it is possible to determine whether the converter 4a has stopped or not based on the control information inside the control unit 4b, and the processing from the stopping of the converter 4a to the start of detection of a break in the cables 6a, 6b by the break detection device 10c can be realized with a simpler configuration.

[0078] This embodiment includes the following aspects: (Supplementary Note 1) A wire-break detection device used in a photovoltaic power generation system including: a solar panel; and a power conversion device connected to the solar panel via a pair of cables and also connected to an AC power grid, converting DC power output from the solar panel into AC power according to the power grid and supplying the converted AC power to the power grid, the wire-break detection device comprising: a measurement circuit connected to at least one of the pair of cables, and measuring measurement data related to a wire-break in the pair of cables at any desired timing by inputting a measurement signal to the at least one cable when the power conversion device is stopped, a memory unit storing a determination value based on the measurement data measured by the measurement circuit, and a detection unit that, after the memory unit stores the determination value, compares the measurement data measured by the measurement circuit with the determination value, and detects a wire-break in the pair of cables when the measurement data has changed by a predetermined amount compared to the determination value, and outputs an alarm signal.

[0079] (Supplementary Note 2) In the disconnection detection device according to Supplementary Note 1, the storage unit resets the judgment value each time the operation of the power conversion device stops, based on the initial measurement data measured by the measurement circuit after the power conversion device stops supplying the AC power to the power grid.

[0080] (Supplementary Note 3) The disconnection detection device according to Supplementary Note 1 or 2, wherein the storage unit stores the determination value based on an average value of a plurality of pieces of measurement data acquired by performing measurements on the measurement circuit several times.

[0081] (Supplementary Note 4) The disconnection detection device according to any one of Supplementary Notes 1 to 3, wherein the detection unit is connected to an alarm that outputs at least one of light and sound as an alarm, and outputs the alarm signal to the alarm, thereby causing the alarm to issue an alarm when a disconnection of the pair of cables is detected.

[0082] (Supplementary Note 5) The disconnection detection device according to any one of Supplementary Notes 1 to 4, wherein the detection unit communicates with an external device and outputs the alarm signal to the external device.

[0083] (Appendix 6) The disconnection detection device according to any one of Appendices 1 to 5, wherein the measurement circuit is connected to each of the pair of cables, inputs the pulsed measurement signal between the pair of cables, and measures the reflected wave of the measurement signal from the pair of cables as the measurement data.

[0084] (Appendix 7) A disconnection detection device according to any one of Appendices 1 to 6, further comprising a ground terminal set to a ground potential, wherein the measurement circuit is connected to one of the pair of cables and also to the ground terminal, and measures the magnitude of the electrostatic capacitance between the one of the pair of cables and the ground terminal as the measurement data.

[0085] (Supplementary Note 8) A wire break detection method used in a photovoltaic power generation system including: a solar panel; and a power conversion device connected to the solar panel via a pair of cables and also connected to an AC power grid, converting DC power output from the solar panel into AC power according to the power grid and supplying the converted AC power to the power grid, the wire break detection method comprising the steps of: connecting a measurement circuit to at least one of the pair of cables, and inputting a measurement signal from the measurement circuit to the at least one cable when the power conversion device is stopped, thereby measuring measurement data related to a wire break in the pair of cables at any timing; storing a determination value based on the measurement data measured by the measurement circuit in a memory unit; comparing the measurement data measured by the measurement circuit with the determination value after the memory unit has stored the determination value, and causing the detection unit to detect a wire break in the pair of cables when the measurement data has changed by a predetermined amount compared to the determination value; and outputting an alarm signal from the detection unit in response to detection of a wire break in the pair of cables.

[0086] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0087] DESCRIPTION OF SYMBOLS 2, 2a to 2c... Photovoltaic power generation system, 3... Solar panel, 4... Power conversion device, 4a... Converter, 4b... Control unit, 4c... Housing, 5... Current collection box, 6a, 6b... Cable, 10, 10a to 10c... Disconnection detection device, 12, 12a... Measuring circuit, 14... Memory unit, 16... Detection unit, 18... Alarm, 20... Ground terminal, 30... External device, PS... Power system

Claims

1. A wire break detection device used in a photovoltaic power generation system comprising: a solar panel; and a power conversion device connected to the solar panel via a pair of cables and also connected to an AC power grid, converting DC power output from the solar panel into AC power according to the power grid and supplying the converted AC power to the power grid; the wire break detection device comprising: a measurement circuit connected to at least one of the pair of cables, and measuring measurement data related to a wire break in the pair of cables at any timing by inputting a measurement signal to the at least one cable when the power conversion device is stopped; a memory unit that stores a judgment value based on the measurement data measured by the measurement circuit; and a detection unit that compares the measurement data measured by the measurement circuit with the judgment value after the memory unit has stored the judgment value, and detects a wire break in the pair of cables when the measurement data has changed by a predetermined amount compared to the judgment value, and outputs an alarm signal.

2. The disconnection detection device according to claim 1, wherein the memory unit resets the judgment value each time the operation of the power conversion device is stopped based on the initial measurement data measured by the measurement circuit after the power conversion device has stopped supplying AC power to the power grid.

3. The disconnection detection device according to claim 1, wherein the storage unit stores the judgment value based on the average value of a plurality of pieces of measurement data obtained by performing measurements on the measurement circuit several times.

4. A disconnection detection device as described in claim 1, wherein the detection unit is connected to an alarm that outputs at least one of light and sound as an alarm, and outputs the alarm signal to the alarm, causing the alarm to sound when a disconnection of the pair of cables is detected.

5. The disconnection detection device according to claim 1, wherein the detection unit communicates with an external device and outputs the alarm signal to the external device.

6. A disconnection detection device according to claim 1, wherein the measurement circuit is connected to each of the pair of cables, inputs a pulsed measurement signal between the pair of cables, and measures the reflected wave of the measurement signal from the pair of cables as the measurement data.

7. A wire break detection device as described in claim 1, further comprising a ground terminal set to ground potential, wherein the measurement circuit is connected to one of the pair of cables and also to the ground terminal, and measures the magnitude of the electrostatic capacitance between the one of the pair of cables and the ground terminal as the measurement data.

8. A wire break detection method used in a photovoltaic power generation system including: a solar panel; and a power conversion device connected to the solar panel via a pair of cables and also connected to an AC power grid, converting DC power output from the solar panel into AC power according to the power grid, and supplying the converted AC power to the power grid, the wire break detection method comprising the steps of: connecting a measurement circuit to at least one of the pair of cables, and inputting a measurement signal from the measurement circuit to the at least one cable when the power conversion device is stopped, thereby measuring measurement data related to a wire break in the pair of cables at any timing; storing a judgment value based on the measurement data measured by the measurement circuit in a memory unit; comparing the measurement data measured by the measurement circuit with the judgment value after the memory unit has stored the judgment value, and causing the detection unit to detect a wire break in the pair of cables when the measurement data has changed by a predetermined amount compared to the judgment value; and outputting an alarm signal from the detection unit in response to detection of a wire break in the pair of cables.

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