Photovoltaic power generation system and method for detecting ground fault in photovoltaic power generation system

Abstract

To provide a photovoltaic power generation system with improved detection accuracy of a ground fault location.SOLUTION: A photovoltaic power generation system comprises a device for detecting a ground fault of a photovoltaic (PV) string 10 in which photovoltaic (PV) modules 12 are connected with each other via respective power optimizers (PO) 20, and the ground fault detection device combines a Voc Shift method and a self-bias method. In the Voc shift method, all the POs 20 are brought into a low voltage mode, the POs 20 are switched into a Voc mode sequentially one by one, and an m-th PV module 12 including a ground fault location and a cable way 16 thereof are narrowed based on changes of VPG and VNG of the PV string 10. In the self-bias method, the POs 20 are brought into the Voc mode or the low voltage mode and VG is calculated from calculation formulas of VPG and VNG based on the calculated m, an output voltage of the PO 20 and a ground fault bias VG and measurements of VPG and VNG, and then, the ground fault location of the PV string 10 is determined based on the calculated VG.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a photovoltaic power generation system and a method for detecting a ground fault in a photovoltaic power generation system. [Background technology]

[0002] A photovoltaic power generation system includes a photovoltaic string in which a plurality of photovoltaic modules are connected in series, and a power conditioner (also called a power conditioning system: PCS) that converts DC power from the photovoltaic string into desired AC power or DC power. In such a photovoltaic power generation system, a ground fault may occur in the electric circuit of the photovoltaic string due to aging deterioration of the covering material of the electric circuit of the photovoltaic string, etc.

[0003] A self-bias method is known as a method for detecting a ground fault. Patent Document 1 discloses a method for detecting a ground fault position of a solar cell string using the self-bias method. Specifically, the positive electrode (P terminal) of the solar cell string is grounded via a detection resistor, and a first voltage, which is a voltage to ground across the detection resistor, is obtained. In addition, the negative electrode (N terminal) of the solar cell string is grounded via a detection resistor, and a second voltage, which is a voltage to ground across the detection resistor, is obtained. Then, the ground fault position is obtained from the ratio of the absolute values ​​of the first voltage and the second voltage.

[0004] Another method for detecting a ground fault is the Voc shift method. Patent Document 2 discloses a method for detecting a ground fault position in a solar cell string using the Voc shift method. Specifically, in a solar cell string in which solar cell modules are connected in series via optimizers (switches), all optimizers are connected. Then, the optimizers are sequentially switched to a disconnected state one by one to determine the ground fault position. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-101012 A [Patent Document 2] JP 2017-187344 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, Patent Documents 1 and 2 aim to detect a ground fault in the electric circuit of a solar cell string caused by aging deterioration of a covering member of the electric circuit of the solar cell string. Meanwhile, in recent years, there has been a demand for detecting a ground fault inside a solar cell module of a solar cell string, in other words, for identifying a solar cell module in which a ground fault has occurred. Furthermore, there has been a demand for identifying whether the ground fault is located inside the solar cell module or in the electric circuit.

[0007] Conventionally, photovoltaic power generation systems are often installed on flat ground, slopes, or roofs of houses or buildings. In such locations, the location of a ground fault can be identified on-site by sequentially accessing each solar cell module and each electrical circuit. However, in recent years, photovoltaic power generation systems are sometimes installed in locations where maintenance is difficult, such as on the walls of buildings or on water. In such locations, it is difficult to sequentially access each solar cell module and each electrical circuit, and it is difficult to identify the location of a ground fault on-site. Therefore, there is a demand for identifying the solar cell module or electrical circuit in which a ground fault has occurred.

[0008] In the self-bias method, the solar cell module with a ground fault may be mistakenly detected as a normal solar cell module adjacent to the solar cell module with a ground fault. As described above, in the self-bias method, the position of the ground fault in the solar cell string is identified from the ratio of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string. However, since the output voltage of the solar cell module varies, if a ground fault occurs at the end of the positive potential side or the negative potential side of the solar cell module, the self-bias method may mistakenly detect the normal solar cell module adjacent to the solar cell module.

[0009] On the other hand, the Voc shift method only observes the changes in the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string when switching the power optimizers one by one in sequence, utilizing the fact that the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change before and after crossing the ground fault position. Therefore, while the Voc shift method can narrow down the ground fault position to one solar cell module and its electric circuit, it cannot identify whether the ground fault position is inside the solar cell module or in the electric circuit.

[0010] An object of the present invention is to provide a photovoltaic power generation system and a method for detecting a ground fault in a photovoltaic power generation system that improves the accuracy of detecting a ground fault position. [Means for solving the problem]

[0011] The photovoltaic power generation system according to the present invention is a photovoltaic power generation system including a photovoltaic string in which M photovoltaic modules are connected in series, and a ground fault detection device that detects a ground fault in the photovoltaic string (M is an integer of 2 or more). The photovoltaic string includes an electric path, M power optimizers connected in series via the electric path, and the M photovoltaic modules that correspond one-to-one to the M power optimizers and are connected in series via the corresponding power optimizers. The power optimizer has a switching function between a Voc mode that outputs an output voltage Voc of the photovoltaic module and a low voltage mode that outputs a predetermined low voltage, and has a common potential at the input and output. The ground fault detection device combines ground fault detection using a Voc shift method and ground fault detection using a self-bias method. In ground fault detection using the Voc shift method, all of the M power optimizers are set to the low voltage mode, and the M power optimizers are switched to the Voc mode one by one in sequence, and the mth solar cell module including the ground fault location and its electrical circuit are narrowed down based on changes in the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string and the polarity of the input / output common potential of the power optimizers (m is an integer between 1 and M). In earth fault detection using the self-bias method, the M power optimizers are set in the Voc mode or the low voltage mode, and an earth fault bias is calculated from a calculation formula for the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string based on the calculated m, the output voltage of the power optimizer, and the earth fault bias generated on the input / output common potential side of the power optimizer, and from the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string (here, the output voltage of the power optimizer is Voc or low voltage), and the position of the earth fault of the solar cell string is identified based on the calculated earth fault bias.

[0012] The method for detecting a ground fault in a photovoltaic power generation system according to the present invention is a method for detecting a ground fault in a photovoltaic power generation system including a photovoltaic string in which M photovoltaic modules are connected in series (M is an integer of 2 or more). The photovoltaic string includes an electric path, M power optimizers connected in series via the electric path, and the M photovoltaic modules that correspond one-to-one to the M power optimizers and are connected in series via the corresponding power optimizers. The power optimizer has a switching function between a Voc mode that outputs an output voltage Voc of the photovoltaic module and a low voltage mode that outputs a predetermined low voltage, and has a common potential at the input and output. The method for detecting a ground fault combines ground fault detection using a Voc shift method and ground fault detection using a self-bias method. In ground fault detection using the Voc shift method, all of the M power optimizers are set to the low voltage mode, and the M power optimizers are switched to the Voc mode one by one in sequence, and the mth solar cell module including the ground fault location and its electrical circuit are narrowed down based on changes in the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string and the polarity of the input / output common potential of the power optimizers (m is an integer between 1 and M). In earth fault detection using the self-bias method, the M power optimizers are set in the Voc mode or the low voltage mode, and an earth fault bias is calculated from a calculation formula for the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string based on the calculated m, the output voltage of the power optimizer, and the earth fault bias generated on the input / output common potential side of the power optimizer, and from the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string (here, the output voltage of the power optimizer is Voc or low voltage), and the position of the earth fault of the solar cell string is identified based on the calculated earth fault bias. Effect of the Invention

[0013] According to the present invention, it is possible to improve the accuracy of detecting a ground fault position of a solar cell string in a solar power generation system. [Brief description of the drawings]

[0014] [Figure 1] 1 is a diagram showing a configuration of a solar power generation system according to a first embodiment. [Diagram 2] 2 is a diagram showing a configuration of a power optimizer in the solar power generation system shown in FIG. [Diagram 3] 2 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 1. [Figure 4] 2 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 1. [Diagram 5] FIG. 1 is a diagram showing a conventional solar cell string. [Figure 6] FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground VPG and the negative potential side voltage to ground VNG of a solar cell string using the Voc shift method (verification 1: one-point ground fault). [Figure 7] FIG. 11 is a diagram showing the measurement results of the positive potential side voltage to ground VPG and the negative potential side voltage to ground VNG of a solar cell string using a self-bias method (verification 1: one-point ground fault). [Figure 8] FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground VPG and the negative potential side voltage to ground VNG of a solar cell string using the Voc shift method (verification 2: two-point ground fault). [Figure 9] FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground VPG and the negative potential side voltage to ground VNG of a solar cell string using a self-bias method (verification 2: two-point ground fault). [Figure 10] FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground VPG and the negative potential side voltage to ground VNG of a solar cell string using a self-bias method (verification 2: two-point ground fault). [Figure 11] FIG. 11 is a diagram showing a configuration of a solar power generation system according to a second embodiment. [Figure 12] 12 is a diagram illustrating a configuration of a power optimizer in the solar power generation system shown in FIG. [Figure 13] FIG. 12 is a diagram showing a solar cell string in the solar power generation system shown in FIG. [Figure 14] FIG. 12 is a diagram showing a solar cell string in the solar power generation system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals. For convenience, hatching and reference numerals may be omitted, in which case other drawings shall be referred to.

[0016] [First embodiment] (Photovoltaic power generation system) Fig. 1 is a diagram showing the configuration of a solar power generation system according to the first embodiment. As shown in Fig. 1, the solar power generation system 1 includes a solar cell string 10 in which M solar cell (also referred to as Photovoltaic: PV) modules 12 are connected in series, and a power conditioner (also referred to as Power Conditioning System: PCS) 30 (M is an integer of 2 or more).

[0017] The solar cell string 10 includes M solar cell modules 12, M power optimizers (PO) 20, and an electrical circuit 16. The M solar cell modules 12 and the M power optimizers 20 are in one-to-one correspondence, and the M power optimizers 20 are connected in series via the electrical circuit 16. As a result, the M solar cell modules 12 are connected in series via the corresponding power optimizers 20. The solar cell module 12 includes a plurality of solar cell cells (or solar cell panels) 14 connected in series.

[0018] The electric circuit 16 is a member that connects adjacent solar cell modules 12, and includes not only wiring members but also wiring members leading from the solar cell modules 12, such as terminal boxes of the solar cell modules 12, and the like.

[0019] Fig. 2 is a diagram showing a configuration of a power optimizer in the solar power generation system shown in Fig. 1. As shown in Fig. 2, the power optimizer 20 includes a power conversion unit 22 and a low voltage generation unit 24. The power conversion unit 22 converts DC power from the solar cell module 12 into DC power. The power conversion unit 22 may have a maximum power point tracking (MPPT) function that tracks the optimal operating point (maximum power point) of the output power of the solar cell module 12. The low voltage generation unit 24 generates a predetermined low voltage (for example, 1 V).

[0020] The power optimizer 20 outputs either the output of the power conversion unit 22 or the output of the low voltage generation unit 24. In this way, the power optimizer 20 has a switching function between a Voc mode in which the output voltage Voc (e.g., 50 V) of the solar cell module 12 is output, and a low voltage mode in which a predetermined low voltage (e.g., 1 V) is output. The power optimizer 20 has a communication function such as power line communication or wireless communication, and switches between the Voc mode and the low voltage mode according to a control signal from the ground fault detection device 32 in the power conditioner 30. In the first embodiment, the negative potential side of the input and the negative potential side of the output in the power optimizer 20 are at a common potential.

[0021] 1 again, the power conditioner 30 converts DC power from the solar cell string 10 into desired AC power or DC power. The power conditioner 30 may have a maximum power point tracking (MPPT) function that tracks an optimal operating point (maximum power point) of the output power of the solar cell string 10. The power conditioner 30 includes a ground fault detection device 32. Note that the location of the ground fault detection device 32 is not limited thereto, and it may be located in any one of the power optimizers 20, or may be mounted in another portion of the solar power generation system 1.

[0022] The ground fault detection device 32 detects a ground fault in the solar cell string 10. The ground fault detection device 32 identifies the location of a ground fault in the solar cell string 10 by a ground fault detection method that combines ground fault detection using a Voc shift method and ground fault detection using a self-bias method. The ground fault detection device 32 has a communication function such as power line communication or wireless communication, and controls the power optimizer 20 when detecting a ground fault. The method of detecting a ground fault by the ground fault detection device 32 will be described in detail later.

[0023] The ground fault detection device 32 includes an arithmetic processor such as a DSP (Digital Signal Processor) or an FPGA (Field-Programmable Gate Array). The various functions of the ground fault detection device 32 are realized, for example, by executing predetermined software (programs, applications) stored in a storage unit. The various functions of the ground fault detection device 32 may be realized by a combination of hardware and software, or may be realized only by hardware (electronic circuits).

[0024] The ground fault detection device 32 also includes a rewritable memory such as an EEPROM. The memory stores predetermined software (programs, applications) executed by the above-mentioned arithmetic processor. The memory also stores in advance or temporarily various parameters required for the arithmetic for detecting a ground fault, which will be described later.

[0025] (Earth fault detection method) Hereinafter, a method for detecting a ground fault in a solar cell string 10 by a ground fault detection device 32 will be described with reference to Fig. 3 and Fig. 4, which is a method for detecting a ground fault in a solar cell string 10 by a ground fault detection device 32 in a solar cell power generation system according to a first embodiment. Fig. 3 and Fig. 4 are diagrams showing solar cell strings in the solar cell power generation system shown in Fig. 1, and Fig. 3 shows a form in which a ground fault exists inside the third solar cell module from the positive potential side, while Fig. 4 shows a form in which a ground fault exists near the positive potential side of the third solar cell module from the positive potential side, or near the negative potential side of the second solar cell module from the positive potential side.

[0026] In the first embodiment, the m-th power optimizer 20 among the M power optimizers 20 is the m-th in ascending order from the positive potential side of the solar cell string 10 (m is an integer from 1 to M).

[0027] <Voc Shift Method> First, set all of the M power optimizers 20 to the low voltage mode (e.g., 1V). Next, switch the M power optimizers 20 to the Voc mode (e.g., 50V) one by one in ascending order from the positive potential side of the solar cell string 10. Since the power optimizer set to the Voc mode is shifted in this way, it is referred to as the Voc shift method in the present application. At this time, measure the voltage V PG of the positive potential side of the solar cell string 10 with respect to the ground and the voltage V NG of the negative potential side with respect to the ground.

[0028] Before and after the power optimizer 20 set to the Voc mode crosses the grounding position, V PG and V NG change significantly. Therefore, based on the changes in V PG and V NG , narrow down the m-th solar cell module 12 including the grounding position and its circuit 16. In the first embodiment, the common potential of the input and output of the power optimizer 20 is the negative potential side, and since the power optimizers 20 are switched to the Voc mode in ascending order from the positive potential side of the solar cell string 10, when V PG and V NG change significantly, narrow down the solar cell module 12 corresponding to the power optimizer 20 immediately before the switched power optimizer 20 and its circuit 16 as the m-th solar cell module 12 including the grounding position and its circuit 16.

[0029] "Its circuit" refers to the circuit intervening from the switching switch (see FIG. 2) in the m-th power optimizer 20 to the switching switch (see FIG. 2) in the (m + 1)-th power optimizer 20.

[0030] For example, in the example of FIG. 3, when the fourth power optimizer 20 is switched to the Voc mode, V PG and V NG This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the ground fault position. G is a ground fault bias occurring on the input / output common potential side of the power optimizer 20. m=3 V PG =1V+1V+Voc-V G V NG =-1V-1V-1V-V G m=4 V PG =1V+1V+1V-V G V NG =-1V-1V-Voc-V G

[0031] In the example of FIG. 4, even if a ground fault occurs near the positive potential side terminal of the third solar cell module 12, when the fourth power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=3 V PG =1V+1V+Voc-V G V NG =-1V-1V-1V-V G m=4 V PG =1V+1V+1V-V G V NG =-1V-1V-Voc-V G

[0032] In the example of FIG. 4, even if a ground fault occurs near the negative potential side terminal of the second solar cell module 12, when the third power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the second solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=2 V PG =1V+Voc-V G V NG =-1V-1V-1V-1V-V G m=3 V PG =1V+1V-V G V NG =-1V-1V-1V-Voc-V G

[0033] From the above, even if the ground fault is near the end of the solar cell module, the Voc shift method can accurately identify the m-th solar cell module and its electric circuit, including the ground fault location. However, since the Voc shift method only measures the change in voltage, it cannot identify where the ground fault location is in the m-th solar cell module and its electric circuit. Therefore, the self-bias method is combined as follows.

[0034] <Self-bias method> Next, all of the M power optimizers 20 are set to the low voltage mode (for example, 1 V). If the output of the power optimizers 20 is stable, all of the M power optimizers 20 may be set to the Voc mode (for example, 50 V). Alternatively, as will be verified later, some of the power optimizers 20 may be set to the Voc mode and the rest to the low voltage mode. At this time, the positive potential side ground voltage V of the solar cell string 10 is PG and the negative potential side voltage to ground V NG Measure.

[0035] V PG and V NGThe measured values ​​of and V PG and V NG From the following calculation formula, the ground fault bias V generated on the input / output common potential side of the power optimizer 20 is G Request. V PG = m × Vdc-V G V NG = (Mm) × -Vdc -V G Here, m is m obtained by the Voc shift method, and Vdc is the output voltage of the power optimizer 20 (Voc (for example, 50 V) or low voltage mode (for example, 1 V)).

[0036] And the obtained earth fault bias V G Specifically, the ground fault position of the solar cell string 10 is identified based on the obtained ground fault bias V G If the ground-fault bias V is greater than 0 V and smaller than Voc (for one solar cell module), it is determined that a ground fault exists in the m-th solar cell module 12 narrowed down by the ground-fault detection using the Voc shift method. G From the magnitude of the ground fault, it is possible to identify which solar cell (or solar panel) in the solar cell module 12 has a ground fault.

[0037] On the other hand, the obtained earth fault bias V G is 0 V, it is determined that a ground fault occurs in the electric circuit 16 connected to the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method.

[0038] The obtained earth fault bias V G If is greater than or equal to Voc (the voltage of one solar cell module) or less than 0 V, it is determined that the narrowing down of the earth fault detection using the Voc shift method is incorrect, and it is determined that earth faults exist in two or more locations. Details will be explained in the verification section below.

[0039] As shown in FIG. 5, in the case of a conventional ground fault detection method using a self-bias method for a solar cell string 10X that does not include a power optimizer, the positive potential side ground voltage V PG and the negative potential side voltage to ground V NG The position of the ground fault in the solar cell string 10X is identified from the ratio of the positive potential side to the negative potential side. However, since there is variation in the output voltage of the solar cell module 12, if there is a ground fault near the end of the positive potential side or the negative potential side of the solar cell module 12, the adjacent normal solar cell module 12 may be erroneously detected. For example, in the example of Fig. 5, a ground fault near the positive potential side of the third solar cell module 12 from the positive potential side may be erroneously detected as a ground fault near the negative potential side of the second solar cell module 12 from the positive potential side.

[0040] On the other hand, in detecting a ground fault using the Voc shift method, as described above, even if the ground fault is located near the end of the solar cell module 12, the m-th solar cell module 12 and its electric circuit 16 including the ground fault location can be accurately identified. However, in the Voc shift method, when the power optimizers 20 are switched one by one in sequence, the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string 10 change before and after crossing the ground fault position. This is utilized to simply observe the changes in the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string 10, so it is not possible to identify where the ground fault position is in the mth solar cell module 12 and its circuit 16.

[0041] Regarding this point, according to the ground fault detection device of the photovoltaic power generation system of the first embodiment and the method for detecting the ground fault of the photovoltaic string by the ground fault detection device, by combining the ground fault detection using the Voc shift method and the ground fault detection using the self-bias method, the detection accuracy of the ground fault position can be improved. Therefore, at the maintenance site, the ground fault position of the photovoltaic string can be specified without accessing each photovoltaic module and each circuit. As a result, even in places where maintenance is difficult, such as the wall surface of a building or on water, the workability of maintenance, such as replacing only the photovoltaic module or photovoltaic cell (photovoltaic panel) where the ground fault has occurred, can be improved. Hereinafter, the above-described effects will be verified.

[0042] (Verification 1) A photovoltaic string of the first embodiment (FIG. 3) in which 14 power optimizers 20 are connected in series and 14 photovoltaic modules 12 are connected in series was prepared. In this photovoltaic string 10, it is previously known that there is a ground fault near the negative potential side of the seventh photovoltaic module 12.

[0043] <Voc shift method> All 14 power optimizers 20 were set to the low voltage mode (1V), and the power optimizers 20 with m = 3 to 12 were switched to the Voc mode (about 50V) one by one in ascending order from the positive potential side. At this time, the positive potential side-to-ground voltage V PG and the negative potential side-to-ground voltage V NG of the photovoltaic string 10 were measured, and the results are shown in FIG. 6.

[0044] As shown in FIG. 6, according to the Voc shift method, when V PG and V NG changed significantly, the photovoltaic module 12 corresponding to the power optimizer 20 immediately before the switched power optimizer 20 could be narrowed down to the seventh photovoltaic module 12 including the ground fault position.

[0045] <Self-bias method> Focusing on the vicinity of m=7, if the power optimizers 20 with m=5 to 10 are in Voc mode (about 50 V) and the power optimizers 20 with m=1 to 4 and m=11 to 14 are in low voltage mode (1 V), the voltage of each power optimizer 20 in the solar cell string 10 is as shown in FIG. 7. In FIG. 7, the vertical axis represents the voltage (relative value) when the positive potential-negative potential voltage of the solar cell string 10 is taken as 100%, that is, the voltage (relative value) when the positive potential side is 0% and the negative potential side is 100%. In addition, based on the previously known ground-fault position near the negative potential side of the seventh solar cell module 12, the positive potential side to ground voltage V PG and the negative potential side voltage to ground V NG Calculate V PG / (V PG +V NG ) is shown by the dashed line.

[0046] At this time, the positive potential side voltage V PG and the negative potential side voltage to ground V NG Based on the measured value of V PG / (V PG +V NG The measured value of ) was 50.4%, as shown by the solid line, which agreed well with the calculated value of 50.1% mentioned above.

[0047] From this, as mentioned above, V PG and V NG The measured value of V and the Voc shift method using m=7 PG and V NG From the following calculation formula, the earth fault bias V G It can be seen that by determining this, it is possible to identify that a ground fault occurs in the vicinity of the negative potential side of the m=7th solar cell module 12. V PG = m × Vdc-V G V NG = (Mm) × -Vdc -V G

[0048] (Verification 2) A solar cell string according to the first embodiment (FIG. 3) was prepared, in which 14 power optimizers 20 were connected in series, and a solar cell string 10 in which 14 solar cell modules 12 were connected in series. In this solar cell string 10, it is known in advance that there are ground faults at two locations, near the negative potential side of the sixth solar cell module 12 and near the negative potential side of the twelfth solar cell module 12.

[0049] <Voc Shift Method> All of the 14 power optimizers 20 were set to the low voltage mode (1V), and the power optimizers 20 with m = 2 to 13 were switched one by one to the Voc mode (about 50V) in ascending order from the positive potential side. At this time, the positive potential side-to-ground voltage V PG and the negative potential side-to-ground voltage V NG of the solar cell string 10 were measured, and the results are shown in FIG. 8.

[0050] As shown in FIG. 6, according to the Voc shift method, when V PG and V NG changed significantly, the solar cell module 12 corresponding to the power optimizer 20 immediately before the switched power optimizer 20 could be narrowed down to the twelfth solar cell module 12 including the ground fault position. However, the sixth solar cell module 12 including the ground fault position could not be identified. Thus, it can be seen that when there are two or more ground faults, one ground fault position can be accurately narrowed down, but the other ground fault positions cannot be identified.

[0051] <Self-Bias Method> First, focusing on the vicinity of m=12, if the power optimizers 20 for m=9 to 14 are in Voc mode (about 50 V) and the power optimizers 20 for m=1 to 8 are in low voltage mode (1 V), the voltage of each power optimizer 20 in the solar cell string 10 is as shown in FIG. 9. In FIG. 9, the vertical axis represents the voltage (relative value) when the voltage of the positive potential-negative potential of the solar cell string 10 is taken as 100%, that is, the voltage (relative value) when the positive potential side is 0% and the negative potential side is 100%. Also, based on the previously known ground-fault position near the negative potential side of the 12th solar cell module 12, the positive potential side to ground voltage V PG and the negative potential side voltage to ground V NG Calculate V PG / (V PG +V NG ) is shown by the dashed line.

[0052] At this time, the positive potential side voltage V PG and the negative potential side voltage to ground V NG Based on the measured value of V PG / (V PG +V NG ) was 26.1%, as shown by the solid line, which differed from the calculated value of 68.9% by more than one Voc.

[0053] From this, as mentioned above, V PG and V NG Measured values ​​of V and V using m=12 obtained by the Voc shift method PG and V NG From the following calculation formula, the earth fault bias V G When we calculate it, we find that it differs by more than one Voc. V PG = m × Vdc-V G V NG = (Mm) × -Vdc -V G

[0054] <Self-bias method> Next, focusing on the vicinity of m=6, if the power optimizers 20 with m=5 to 10 are in Voc mode (about 50 V) and the power optimizers 20 with m=1 to 4 and m=11 to 14 are in low voltage mode (1 V), the voltage of each power optimizer 20 in the solar cell string 10 is as shown in FIG. 10. In FIG. 10, the vertical axis represents the voltage (relative value) when the voltage of the positive potential-negative potential of the solar cell string 10 is taken as 100%, that is, the voltage (relative value) when the positive potential side is 0% and the negative potential side is 100%. Also, based on the previously known ground-fault position near the negative potential side of the sixth solar cell module 12, assuming a single-point ground fault, the positive potential side to ground voltage V PG and the negative potential side voltage to ground V NG Calculate V PG / (V PG +V NG ) is shown by the dashed line.

[0055] At this time, the positive potential side voltage V PG and the negative potential side voltage to ground V NG Based on the measured value of V PG / (V PG +V NG ) was 57.4%, as shown by the solid line, which differed from the calculated value of 33.7% by more than one Voc.

[0056] From this, as mentioned above, V PG and V NG Measured values ​​of V and V using m=12 obtained by the Voc shift method PG and V NG From the following calculation formula, the earth fault bias V G When we calculate it, we find that it differs by more than one Voc. V PG = m × Vdc-V G V NG = (Mm) × -Vdc -V G

[0057] Note that, as described above, in the Voc shift method, since one of the two grounding positions can be accurately identified, first, the solar cell module 12 with m = 12 and its circuit 16 are maintained based on the Voc shift method, and then, it is conceivable to perform again the grounding detection method that combines the grounding detection using the Voc shift method described above and the grounding detection using the self - bias method. Even so, if the presence of two or more ground faults is detected, it is conceivable to repeat the above - mentioned method.

[0058] (Modification of the First Embodiment) In the first embodiment, in the Voc shift method, the M power optimizers 20 are switched to the Voc mode one by one in ascending order from the positive potential side of the solar cell string 10. However, in the Voc shift method, the M power optimizers 20 may be switched to the Voc mode one by one in descending order from the negative potential side of the solar cell string 10.

[0059] <Voc Shift Method> First, all of the M power optimizers 20 are set to the low - voltage mode (for example, 1V). Next, the M power optimizers 20 are switched to the Voc mode (for example, 50V) one by one in descending order from the negative potential side of the solar cell string 10. At this time, the positive - potential - side - to - ground voltage V PG and the negative - potential - side - to - ground voltage V NG are measured.

[0060] Before and after the power optimizer 20 set to the Voc mode straddles the grounding position, V PG and V NG change significantly. Therefore, based on the changes in V PG and V NG the m - th solar cell module 12 including the grounding position and its circuit 16 are narrowed down. In this modification, the input - output common battery of the power optimizer 20 is on the negative potential side, and since the power optimizers 20 are switched to the Voc mode in descending order from the negative potential side of the solar cell string 10, V PG and V NGIf there is a large change, the solar cell module 12 and its electric circuit 16 corresponding to the switched power optimizer 20 are narrowed down to the m-th solar cell module 12 and its electric circuit 16 including the ground fault location.

[0061] For example, in the example of FIG. 3, when the third power optimizer 20 is switched to the Voc mode, V PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=4 V PG =1V+1V+1V-V G V NG =-1V-1V-Voc-V G m=3 V PG =1V+1V+Voc-V G V NG =-1V-1V-1V-V G

[0062] In the example of FIG. 4, even if a ground fault occurs near the positive potential side terminal of the third solar cell module 12, when the third power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=4 V PG =1V+1V+1V-V G V NG =-1V-1V-Voc-V G m=3 V PG =1V+1V+Voc-V G V NG =-1V-1V-1V-V G

[0063] In the example of FIG. 4, even if a ground fault occurs near the negative potential side terminal of the second solar cell module 12, when the second power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the second solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=3 V PG =1V+1V-V G V NG =-1V-1V-1V-Voc-V G m=2 V PG =1V+Voc-V G V NG =-1V-1V-1V-1V-V G

[0064] <Self-bias method> Next, all of the M power optimizers 20 are set to the low voltage mode (for example, 1 V). If the output of the power optimizers 20 is stable, all of the M power optimizers 20 may be set to the Voc mode (for example, 50 V). Alternatively, as in the above-mentioned verification, some of the power optimizers 20 may be set to the Voc mode and the rest may be set to the low voltage mode. At this time, the positive potential side ground voltage V of the solar cell string 10 is PG and the negative potential side voltage to ground V NG Measure.

[0065] V PG and V NG The measured values ​​of and V PG and V NG From the following calculation formula, the ground fault bias V generated on the input / output common potential side of the power optimizer 20 is G Request. V PG = m × Vdc-V G V NG = (Mm) × -Vdc -V G

[0066] And the obtained earth fault bias V G Specifically, the ground fault position of the solar cell string 10 is identified based on the obtained ground fault bias V G If the ground-fault bias V is greater than 0 V and smaller than Voc (for one solar cell module), it is determined that a ground fault exists in the m-th solar cell module 12 narrowed down by the ground-fault detection using the Voc shift method. G From the magnitude of the ground fault, it is possible to identify which solar cell (or solar panel) in the solar cell module 12 has a ground fault.

[0067] On the other hand, the obtained earth fault bias V G is 0 V, it is determined that a ground fault occurs in the electric circuit 16 connected to the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method.

[0068] The obtained earth fault bias V G If is greater than or equal to Voc (the voltage of one solar cell module) or less than 0 V, it is determined that the narrowing down of the earth fault detection using the Voc shift method is incorrect, and it is determined that earth faults exist at two or more locations.

[0069] [Second embodiment] (Photovoltaic power generation system) Fig. 11 is a diagram showing the configuration of a solar power generation system according to the second embodiment. The solar power generation system 1 shown in Fig. 11 differs from the solar power generation system 1 of the first embodiment shown in Fig. 1 in the configuration of the power optimizer 20 and the function and operation of the ground fault detection device 32.

[0070] FIG. 12 is a diagram showing the configuration of the power optimizer in the photovoltaic power generation system shown in FIG. 11. The power optimizer 20 shown in FIG. 12 is different from the power optimizer 20 of the first embodiment shown in FIG. 2 in terms of the input / output common potential. In the first embodiment, the negative potential side of the input and the negative potential side of the output in the power optimizer 20 were at the common potential. In the second embodiment, the positive potential side of the input and the positive potential side of the output in the power optimizer 20 are at the common potential.

[0071] (Ground fault detection method) Hereinafter, with reference to FIGS. 13 and 14, a ground fault detection method for a photovoltaic power generation system according to the second embodiment, which is a ground fault detection method for the solar cell string 10 by the ground fault detection device 32, will be described. FIGS. 13 and 14 are diagrams showing the solar cell string in the photovoltaic power generation system shown in FIG. 11. In FIG. 1 3, a form in which there is a ground fault inside the third solar cell module from the negative potential side is shown. In FIG. 1 4, a form in which there is a ground fault near the negative potential side of the third solar cell module from the negative potential side, or near the positive potential side of the second PV module from the negative potential side is shown.

[0072] In the first embodiment, the m-th power optimizer 20 among the M power optimizers 20 was the m-th in ascending order from the positive potential side of the solar cell string 10. In the second embodiment, the m-th power optimizer 20 among the M power optimizers 20 is the m-th in ascending order from the negative potential side of the solar cell string 10.

[0073] <Voc shift method> First, set all of the M power optimizers 20 to the low voltage mode (for example, 1V). Next, switch the M power optimizers 20 to the Voc mode (for example, 50V) one by one in ascending order from the negative potential side of the solar cell string 10. At this time, measure the positive potential side-to-ground voltage V PG and the negative potential side-to-ground voltage V NG of the solar cell string 10.

[0074] The power optimizer 20 in Voc mode changes V before and after crossing the ground fault position. PG and V NG changes significantly, so V PG and V NG Based on the change in V, the m-th solar cell module 12 and its electric circuit 16 including the ground fault location are narrowed down. In the second embodiment, the input / output common potential of the power optimizer 20 is the positive potential side, and the power optimizers 20 are switched to the Voc mode in ascending order from the negative potential side of the solar cell string 10. PG and V NG has changed significantly, the solar cell module 12 and its electric circuit 16 corresponding to the power optimizer 20 immediately preceding the switched power optimizer 20 are narrowed down as the m-th solar cell module 12 and its electric circuit 16 including the ground fault location.

[0075] For example, in the example of FIG. 13, when the fourth power optimizer 20 is switched to the Voc mode, V PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=3 V PG =1V+1V+1V+V G V NG =-1V-1V-Voc+V G m=4 V PG =1V+1V+Voc+V G V NG =-1V-1V-1V+V G

[0076] In the example of FIG. 14, even if a ground fault occurs near the negative potential side terminal of the third solar cell module 12, when the fourth power optimizer 20 is switched to the Voc mode, PG and V NGchanges by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=3 V PG =1V+1V+1V+V G V NG =-1V-1V-Voc+V G m=4 V PG =1V+1V+Voc+V G V NG =-1V-1V-1V+V G

[0077] Also, Fig. 1 In the example of 4, even if a ground fault occurs near the positive potential side terminal of the second solar cell module 12, when the third power optimizer 20 is switched to the Voc mode as follows, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the second solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=2 V PG =1V+1V+1V+1V+V G V NG =-1V-Voc+V G m=3 V PG =1V+1V+1V+Voc+V G V NG =-1V-1V+V G

[0078] From the above, even if the ground fault is near the end of the solar cell module, the Voc shift method can accurately identify the m-th solar cell module and its electric circuit, including the ground fault location. However, since the Voc shift method only measures the change in voltage, it cannot identify where the ground fault location is in the m-th solar cell module and its electric circuit. Therefore, the self-bias method is combined as follows.

[0079] <Self-bias method> Next, all of the M power optimizers 20 are set to the low voltage mode (for example, 1 V). If the output of the power optimizers 20 is stable, all of the M power optimizers 20 may be set to the Voc mode (for example, 50 V). Alternatively, as in the above-mentioned verification, some of the power optimizers 20 may be set to the Voc mode and the rest may be set to the low voltage mode. At this time, the positive potential side ground voltage V of the solar cell string 10 is PG and the negative potential side voltage to ground V NG Measure.

[0080] V PG and V NG The measured values ​​of and V PG and V NG From the following calculation formula, the ground fault bias V generated on the input / output common potential side of the power optimizer 20 is G Request. V PG = (Mm) × Vdc + V G V NG =m × -Vdc + V G

[0081] And the obtained earth fault bias V G Specifically, the ground fault position of the solar cell string 10 is identified based on the obtained ground fault bias V G If the ground-fault bias V is greater than 0 V and smaller than Voc (for one solar cell module), it is determined that a ground fault exists in the m-th solar cell module 12 narrowed down by the ground-fault detection using the Voc shift method. G From the magnitude of the ground fault, it is possible to identify which solar cell (or solar panel) in the solar cell module 12 has a ground fault.

[0082] On the other hand, the obtained earth fault bias V G is 0 V, it is determined that a ground fault occurs in the electric circuit 16 connected to the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method.

[0083] In addition, when the obtained ground connection bias V G is equal to or greater than Voc (for one solar cell module) or less than 0 V, it is determined that the narrowing down of the ground connection detection using the Voc shift method is incorrect, and it is specified that there are ground connections at two or more positions.

[0084] Also, in the ground connection detection device of the photovoltaic power generation system of this second embodiment and the ground connection detection method of the solar cell string by the ground connection detection device, the same advantages as those of the ground connection detection device of the photovoltaic power generation system of the first embodiment and the ground connection detection method of the solar cell string by the ground connection detection device can be obtained.

[0085] (Modification of the second embodiment) In the second embodiment, in the Voc shift method, the M power optimizers 20 are switched to the Voc mode one by one in ascending order from the negative potential side of the solar cell string 10. However, in the Voc shift method, the M power optimizers 20 may be switched to the Voc mode one by one in descending order from the positive potential side of the solar cell string 10.

[0086] <Voc shift method> First, set all of the M power optimizers 20 to the low voltage mode (for example, 1 V). Next, switch the M power optimizers 20 to the Voc mode (for example, Voc) one by one in descending order from the positive potential side of the solar cell string 10. At this time, the positive potential side-to-ground voltage V PG and the negative potential side-to-ground voltage V NG of the solar cell string 10 are measured.

[0087] Before and after the power optimizer 20 set to the Voc mode straddles the ground connection position, V PG and V NG change significantly. Therefore, V PG and V NGBased on the change in V, the m-th solar cell module 12 and its electric circuit 16 including the ground fault location are narrowed down. In this modification, the input / output common battery of the power optimizer 20 is on the positive potential side, and the power optimizers 20 are switched to the Voc mode in descending order from the positive potential side of the solar cell string 10. PG and V NG If there is a large change, the solar cell module 12 and its electric circuit 16 corresponding to the switched power optimizer 20 are narrowed down to the m-th solar cell module 12 and its electric circuit 16 including the ground fault location.

[0088] For example, in the example of FIG. 13, when the third power optimizer 20 is switched to the Voc mode, V PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=4 V PG =1V+1V+Voc+V G V NG =-1V-1V-1V+V G m=3 V PG =1V+1V+1V+V G V NG =-1V-1V-Voc+V G

[0089] In the example of FIG. 14, even if a ground fault occurs near the negative potential side terminal of the third solar cell module 12, when the third power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=4 V PG =1V+1V+Voc+V G V NG =-1V-1V-1V+VG m=3 V PG =1V+1V+1V+V G V NG =-1V-1V-Voc+V G

[0090] In the example of FIG. 14, even if a ground fault occurs near the positive potential side terminal of the second solar cell module 12, when the second power optimizer 20 is switched to the Voc mode, PG and V NG changes by an amount equal to Voc. This makes it possible to accurately identify the second solar cell module 12 and its electric circuit 16, including the location of the ground fault. m=3 V PG =1V+1V+1V+Voc+V G V NG =-1V-1V+V G m=2 V PG =1V+1V+1V+1V+V G V NG =-1V-Voc+V G

[0091] <Self-bias method> Next, all of the M power optimizers 20 are set to the low voltage mode (for example, 1 V). If the output of the power optimizers 20 is stable, all of the M power optimizers 20 may be set to the Voc mode (for example, 50 V). Alternatively, as in the above-mentioned verification, some of the power optimizers 20 may be set to the Voc mode and the rest may be set to the low voltage mode. At this time, the positive potential side ground voltage V of the solar cell string 10 is PG and the negative potential side voltage to ground V NG Measure.

[0092] V PG and V NG The measured values ​​of and V PG and V NGFrom the following calculation formula, the ground fault bias V generated on the input / output common potential side of the power optimizer 20 is G Request. V PG = (Mm) × Vdc + V G V NG =m × -Vdc + V G

[0093] And the obtained earth fault bias V G Specifically, the ground fault position of the solar cell string 10 is identified based on the obtained ground fault bias V G If the ground-fault bias V is greater than 0 V and smaller than Voc (for one solar cell module), it is determined that a ground fault exists in the m-th solar cell module 12 narrowed down by the ground-fault detection using the Voc shift method. G From the magnitude of the ground fault, it is possible to identify which solar cell (or solar panel) in the solar cell module 12 has a ground fault.

[0094] On the other hand, the obtained earth fault bias V G is 0 V, it is determined that a ground fault occurs in the electric circuit 16 connected to the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method.

[0095] The obtained earth fault bias V G If is greater than or equal to Voc (the voltage of one solar cell module) or less than 0 V, it is determined that the narrowing down of the earth fault detection using the Voc shift method is incorrect, and it is determined that earth faults exist at two or more locations.

[0096] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various changes and modifications are possible. [Explanation of symbols]

[0097] 1. Solar power generation system 10 Solar cell string 12 Solar cell module 14 Solar Cell 16 Electric circuit 20 Power Optimizer 22 Power conversion unit, 24 Low voltage generation unit 30 Power Conditioner 32 Earth fault detection device

Claims

1. A solar power generation system including a solar cell string in which M solar cell modules are connected in series, and a ground fault detection device that detects a ground fault in the solar cell string, wherein M is an integer of 2 or more, The solar cell string comprises: Electric circuit and M power optimizers connected in series via the electric paths; the M solar cell modules each corresponding to one of the M power optimizers and connected in series via the corresponding power optimizers; Including, The power optimizer comprises: a Voc mode for outputting an output voltage Voc of the solar cell module and a low voltage mode for outputting a predetermined low voltage; having a common potential at the input and output, The ground fault detection device combines ground fault detection using a Voc shift method and ground fault detection using a self-bias method, In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in sequence to the Voc mode; narrowing down an m-th solar cell module including a ground fault location and its electric circuit based on a change in a positive potential side voltage to ground and a negative potential side voltage to ground of the solar cell string and a polarity of an input / output common potential of the power optimizer, where m is an integer between 1 and M; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; a ground fault bias is calculated from a calculation formula for the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string based on the calculated m, the output voltage of the power optimizer, and a ground fault bias occurring on an input / output common potential side of the power optimizer, and from measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, where the output voltage of the power optimizer is Voc or a low voltage; Identifying a ground fault location of the solar cell string based on the determined ground fault bias. Photovoltaic power generation system.

2. In the ground fault detection using the self-bias method, the ground fault detection device If the determined earth fault bias is greater than 0 V and smaller than Voc, it is determined that an earth fault exists in the m-th solar cell module narrowed down by the earth fault detection using the Voc shift method; If the determined earth fault bias is 0 V, it is determined that an earth fault exists in the electric circuit connected to the m-th solar cell module narrowed down by the earth fault detection using the Voc shift method. The solar power generation system according to claim 1 .

3. In the ground fault detection using the self-bias method, the ground fault detection device if the determined ground fault bias is equal to or greater than Voc or less than 0 V, determining that a ground fault exists at two or more locations; The solar power generation system according to claim 1 or 2.

4. When the input / output common potential of the power optimizer is on the negative potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the positive potential side of the solar cell string, and In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in ascending order from the positive potential side of the solar cell string to the Voc mode; when the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down a solar cell module and its electric circuit corresponding to a power optimizer immediately before the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =m×Vdc-V Ｇ V ＮＧ =(M-m)×-Vdc-V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The solar power generation system according to any one of claims 1 to 3.

5. When the input / output common potential of the power optimizer is on the negative potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the positive potential side of the solar cell string, and In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in descending order from the negative potential side of the solar cell string to the Voc mode; When the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down the solar cell module and its electric circuit corresponding to the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =m×Vdc-V Ｇ V ＮＧ =(M-m)×-Vdc-V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The solar power generation system according to any one of claims 1 to 3.

6. When the input / output common potential of the power optimizers is on the positive potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the negative potential side of the solar cell string, where In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in ascending order from the negative potential side of the solar cell string to the Voc mode; when the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down a solar cell module and its electric circuit corresponding to a power optimizer immediately before the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =(M-M)×Vf+V Ｇ V ＮＧ =m×-Vdc+V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The solar power generation system according to any one of claims 1 to 3.

7. When a common potential of input / output of the power optimizers is on the positive potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the negative potential side of the solar cell string, as follows: In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in descending order from the positive potential side of the solar cell string to the Voc mode; When the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down the solar cell module and its electric circuit corresponding to the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Voc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =(M-M)×Vf+V Ｇ V ＮＧ =m×-Vdc+V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The solar power generation system according to any one of claims 1 to 3.

8. A method for detecting a ground fault in a solar cell string in a solar power generation system including M solar cell modules connected in series, the method comprising: detecting a ground fault in the solar cell string, wherein M is an integer of 2 or more; The solar cell string comprises: Electric circuit and M power optimizers connected in series via the electric paths; the M solar cell modules each corresponding to one of the M power optimizers and connected in series via the corresponding power optimizers; Including, The power optimizer comprises: a Voc mode for outputting an output voltage Voc of the solar cell module and a low voltage mode for outputting a predetermined low voltage; having a common potential at the input and output, The ground fault detection method combines ground fault detection using a Voc shift method and ground fault detection using a self-bias method, In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in sequence to the Voc mode; narrowing down an m-th solar cell module including a ground fault location and its electric circuit based on a change in a positive potential side voltage to ground and a negative potential side voltage to ground of the solar cell string and a polarity of an input / output common potential of the power optimizer, where m is an integer between 1 and M; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; a ground fault bias is calculated from a calculation formula for the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string based on the calculated m, the output voltage of the power optimizer, and a ground fault bias occurring on an input / output common potential side of the power optimizer, and from measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, where the output voltage of the power optimizer is Voc or a low voltage; Identifying a ground fault location of the solar cell string based on the determined ground fault bias. A method for detecting a ground fault in a photovoltaic power generation system.

9. In the earth fault detection using the self-bias method, If the determined earth fault bias is greater than 0 V and smaller than Voc, it is determined that an earth fault exists in the m-th solar cell module narrowed down by the earth fault detection using the Voc shift method; If the determined earth fault bias is 0 V, it is determined that an earth fault exists in the electric circuit connected to the m-th solar cell module narrowed down by the earth fault detection using the Voc shift method. The method for detecting a ground fault in a photovoltaic power generation system according to claim 8.

10. In the earth fault detection using the self-bias method, if the determined ground fault bias is equal to or greater than Voc or less than 0 V, determining that a ground fault exists at two or more locations; The method for detecting a ground fault in a photovoltaic power generation system according to claim 8 or 9.

11. When the input / output common potential of the power optimizer is on the negative potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the positive potential side of the solar cell string, and In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in ascending order from the positive potential side of the solar cell string to the Voc mode; when the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down a solar cell module and its electric circuit corresponding to a power optimizer immediately before the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =m×Vdc-V Ｇ V ＮＧ =(M-m)×-Vdc-V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10.

12. When the input / output common potential of the power optimizer is on the negative potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the positive potential side of the solar cell string, and In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in descending order from the negative potential side of the solar cell string to the Voc mode; When the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down the solar cell module and its electric circuit corresponding to the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =m×Vdc-V Ｇ V ＮＧ =(M-m)×-Vdc-V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10.

13. When the input / output common potential of the power optimizers is on the positive potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the negative potential side of the solar cell string, where In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in ascending order from the negative potential side of the solar cell string to the Voc mode; when the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down a solar cell module and its electric circuit corresponding to a power optimizer immediately before the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Vdc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =(M-M)×Vf+V Ｇ V ＮＧ =m×-Vdc+V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10.

14. When a common potential of input / output of the power optimizers is on the positive potential side of the solar cell string, an m-th power optimizer among the M power optimizers is the m-th power optimizer in ascending order from the negative potential side of the solar cell string, as follows: In the earth fault detection using the Voc shift method, placing all of the M power optimizers in the low voltage mode, and switching the M power optimizers one by one in descending order from the positive potential side of the solar cell string to the Voc mode; When the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string change, narrowing down the solar cell module and its electric circuit corresponding to the switched power optimizer to an m-th solar cell module and its electric circuit including a ground fault location; In the earth fault detection using the self-bias method, placing the M power optimizers in the Voc mode or the low voltage mode; The obtained m, the output voltage Voc of the power optimizer, and the ground fault bias V generated on the input / output common potential side of the power optimizer Ｇ The positive potential side voltage V of the solar cell string based on ＰＧ and the negative potential side voltage to ground V ＮＧ From the following calculation formula and the measured values ​​of the positive potential side voltage to ground and the negative potential side voltage to ground of the solar cell string, the earth fault bias V Ｇ where Vdc is Voc or the low voltage; V ＰＧ =(M-M)×Vf+V Ｇ V ＮＧ =m×-Vdc+V Ｇ Calculated earth fault bias V Ｇ and identifying a ground fault location of the solar cell string based on the The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10.

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