JP7634401B2 - Photovoltaic power generation system and method for detecting ground fault in photovoltaic power generation system - Google Patents

Description

The present invention relates to a solar power generation system and a method for detecting a ground fault in a solar power generation system.

A photovoltaic power generation system includes a photovoltaic string in which multiple 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 the desired AC power or DC power. In such a photovoltaic power generation system, a ground fault may occur in the electrical path of the photovoltaic string due to deterioration over time of the covering material of the electrical path of the photovoltaic string.

The self-bias method is known as a method for detecting a ground fault. Patent Document 1 discloses a method for detecting the position of a ground fault in 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 the 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 the voltage to ground across the detection resistor, is obtained. The position of the ground fault is then obtained from the ratio of the absolute values of the first voltage and the second voltage.

Another method for detecting a ground fault is the Voc shift method. Patent Document 2 discloses a method for detecting the location of a ground fault 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 switched to a disconnected state one by one in order to determine the location of the ground fault.

JP 2016-101012 A JP 2017-187344 A

As described above, Patent Documents 1 and 2 aim to detect ground faults in the electrical paths of a solar cell string caused by aging deterioration of the covering material of the electrical paths of the solar cell string. Meanwhile, in recent years, there has been a demand for detecting ground faults inside the solar cell modules of a solar cell string, in other words, for identifying the solar cell module in which a ground fault has occurred. Furthermore, there has been a demand for identifying whether the location of the ground fault is inside the solar cell module or in the electrical path.

Traditionally, 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 accessing each solar cell module and each electrical circuit in sequence. 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 access each solar cell module and each electrical circuit in sequence, making it difficult to identify the location of a ground fault on-site. For this reason, there is a demand for identifying the solar cell module or electrical circuit in which a ground fault has occurred.

The self-bias method may mistakenly detect a normal solar cell module next to the solar cell module where a ground fault has occurred, rather than the solar cell module where a ground fault has occurred. As described above, the self-bias method identifies the location of a ground fault in a solar cell string from the ratio of the voltage to ground on the positive potential side of the solar cell string to the voltage to ground on the negative potential side. However, because there is variation in the output voltage of solar cell modules, if there is a ground fault at the end of the positive potential side or negative potential side of a solar cell module, the self-bias method may mistakenly detect a normal solar cell module next to it.

On the other hand, the Voc shift method only observes the change 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, taking advantage of 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 electrical circuit, it cannot identify whether the ground fault position is inside the solar cell module or in the electrical circuit.

The present invention aims to provide a solar power generation system and a method for detecting a ground fault in a solar power generation system that improves the accuracy of detecting the location of a ground fault.

The solar power generation system according to the present invention is 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 (M is an integer of 2 or more). The solar cell string includes an electric circuit, M power optimizers connected in series via the electric circuit, and the M solar cell 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 the output voltage Voc of the solar cell 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 (m is an integer between 1 and M) 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. In earth fault detection using the self-bias method, the M power optimizers are set to the Voc mode or the low voltage mode, and an earth fault bias is calculated from the calculated m, the output voltage of the power optimizer, and the 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 earth fault bias generated on the input/output common potential side of the power optimizer, 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 (here, the output voltage of the power optimizer is Voc or low voltage), and the location of the earth fault in the solar cell string is identified based on the calculated earth fault bias.

The ground fault detection method for 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 circuit, M power optimizers connected in series via the electric circuit, 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 the 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 method 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 (m is an integer between 1 and M) 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. In earth fault detection using the self-bias method, the M power optimizers are set to the Voc mode or the low voltage mode, and an earth fault bias is calculated from the calculated m, the output voltage of the power optimizer, and the 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 earth fault bias generated on the input/output common potential side of the power optimizer, 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 (here, the output voltage of the power optimizer is Voc or low voltage), and the location of the earth fault in the solar cell string is identified based on the calculated earth fault bias.

The present invention can improve the accuracy of detecting the location of a ground fault in a solar cell string in a solar power generation system.

1 is a diagram showing a configuration of a solar power generation system according to a first embodiment. 2 is a diagram showing a configuration of a power optimizer in the solar power generation system shown in FIG. 1 . FIG. 2 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 1 . FIG. 2 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 1 . FIG. 1 is a diagram showing a conventional solar cell string. 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 by the Voc shift method (verification 1: one-point ground fault). FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground V _PG and the negative potential side voltage to ground V _NG of a solar cell string by a self-bias method (verification 1: one-point ground fault). 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 by the Voc shift method (verification 2: two-point ground fault). FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground V _PG and the negative potential side voltage to ground V _NG of a solar cell string by a self-bias method (verification 2: two-point ground fault). FIG. 13 is a diagram showing the measurement results of the positive potential side voltage to ground V _PG and the negative potential side voltage to ground V _NG of a solar cell string by a self-bias method (verification 2: two-point ground fault). FIG. 11 is a diagram showing a configuration of a solar power generation system according to a second embodiment. 12 is a diagram showing a configuration of a power optimizer in the solar power generation system shown in FIG. 11 . FIG. 12 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 11 . FIG. 12 is a diagram showing a solar cell string in the solar power generation system shown in FIG. 11 .

Below, an example of an embodiment of the present invention will be described with reference to the attached drawings. Note that the same reference numerals will be used to refer to the same or equivalent parts in each drawing. Also, for convenience, hatching and component reference numerals may be omitted, in which case other drawings shall be referred to.

[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).

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.

The electrical circuit 16 is a component that connects adjacent solar cell modules 12, and includes not only wiring components but also wiring components leading from the solar cell modules 12, such as the terminal boxes of the solar cell modules 12.

Figure 2 is a diagram showing the configuration of a power optimizer in the solar power generation system shown in Figure 1. As shown in Figure 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 (e.g., 1 V).

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.

Referring again to FIG. 1, the power conditioner 30 converts the DC power from the solar cell string 10 into the desired AC power or DC power. The power conditioner 30 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 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 to this, and it may be located in one of the power optimizers 20 or mounted in another part of the solar power generation system 1.

The ground fault detection device 32 detects a ground fault in the solar cell string 10. The ground fault detection device 32 also identifies the location of a ground fault in the solar cell string 10 using a ground fault detection method that combines ground fault detection using the Voc shift method and ground fault detection using the 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.

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).

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 calculation processor described above. The memory also stores in advance or temporarily various parameters required for the calculation for ground fault detection, which will be described later.

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

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

<Voc Shift Method>
First, all of the M power optimizers 20 are set to low voltage mode (e.g., 1 V). Next, the M power optimizers 20 are switched to Voc mode (e.g., 50 V) one by one in ascending order from the positive potential side of the solar cell string 10. Since the power optimizers to be set to Voc mode are shifted in this manner, this method is referred to as a Voc shift method in this application. At this time, the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

Since _VPG and _VNG change significantly before and after the power optimizer 20 in the Voc mode crosses the ground fault position, the m-th solar cell module 12 and its electric circuit 16 including the ground fault position are narrowed down based on the changes in _VPG and _VNG . In the first embodiment, the input/output common potential of the power optimizer 20 is on the negative potential side, and the power optimizers 20 are switched to the Voc mode in ascending order from the positive potential side of the solar cell string 10, so when _VPG and _VNG change 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 position.

"That electrical path" refers to the electrical path from the changeover switch in the mth power optimizer 20 (see FIG. 2) to the changeover switch in the m+1th power optimizer 20 (see FIG. 2).

3, when the fourth power optimizer 20 is switched to the Voc mode, _VPG and _VNG change by Voc as follows. This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the ground fault location. _VG is a ground fault bias generated 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

4, even if a ground fault occurs near the positive potential side terminal of the third solar cell module 12, _VPG and _VNG change by Voc when the fourth power optimizer 20 is switched to the Voc mode as follows. 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

4, even if a ground fault occurs near the negative potential side terminal of the second solar cell module 12, _VPG and _VNG change by Voc when the third power optimizer 20 is switched to the Voc mode as follows. 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
_VPG =1V+Voc- _VG
V _NG =-1V-1V-1V-1V-V _G
m=3
_VPG =1V+1V- _VG
V _NG =-1V-1V-1V-Voc-V _G

As a result, even if the ground fault is near the end of the solar cell module, the Voc shift method can accurately identify the mth solar cell module and its electrical 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 is located relative to the mth solar cell module and its electrical circuit. Therefore, the self-bias method is combined as follows.

<Self-bias method>
Next, all of the M power optimizers 20 are set to the low voltage mode (e.g., 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 (e.g., 50 V). Alternatively, as in the verification described below, 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 voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

The ground fault bias V _G occurring on the input/output common potential side of the power optimizer 20 is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG .
V _PG = m x Vdc - V _G
V _NG = (M-m)×-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)).

Then, the location of the ground fault in the solar cell string 10 is identified based on the obtained ground fault bias V _G. Specifically, if the obtained ground fault bias V _G is greater than 0 V and smaller than Voc (for one solar cell module), it is identified that the ground fault exists inside the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method. Furthermore, it is possible to identify which solar cell (or solar cell panel) in the solar cell module 12 has a ground fault from the magnitude of the obtained ground fault bias V _G.

On the other hand, if the determined ground 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.

If the obtained ground fault bias V _G is equal to or greater than Voc (for one solar cell module) or smaller than 0 V, it is determined that the narrowing down of the ground fault detection using the Voc shift method is incorrect, and it is determined that ground faults exist at two or more positions. Details will be explained in the verification section below.

Here, as shown in Fig. 5, in the conventional ground fault detection by the self-bias method of the solar cell string 10X not provided with a power optimizer, the position of the ground fault of the solar cell string 10X is identified from the ratio of the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10X. However, since there is a variation in the output voltage of the solar cell module 12, when a ground fault exists 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.

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.

In this regard, according to the ground fault detection device of the solar power generation system of the first embodiment and the method of detecting a ground fault in a solar cell string by using the ground fault detection device, the detection accuracy of the ground fault position can be improved by combining ground fault detection using the Voc shift method and ground fault detection using the self-bias method. Therefore, the ground fault position of the solar cell string can be identified at the maintenance site without accessing each solar cell module and each electric circuit. This makes it possible to improve the workability of maintenance, such as replacing only the solar cell module or solar cell (solar panel) in which a ground fault has occurred, even in locations where maintenance is difficult, such as on the wall of a building or on water. The above-mentioned effects will be verified below.

(Verification 1)
A solar cell string 10 according to the first embodiment ( FIG. 3 ) was prepared, in which 14 power optimizers 20 were connected in series and 14 solar cell modules 12 were connected in series. In this solar cell string 10, it was previously known that a ground fault existed near the negative potential side of the seventh solar cell module 12.

<Voc Shift Method>
All 14 power optimizers 20 were set to the low voltage mode (1 V), and the power optimizers 20 (m=3 to 12) were switched to the Voc mode (about 50 V) one by one in ascending order from the positive potential side. The results of measuring the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 at this time are shown in FIG. 6.

As shown in FIG. 6 , according to the Voc shift method, when _VPG and _VNG change significantly, it is possible to narrow down the solar cell module 12 corresponding to the power optimizer 20 immediately preceding the switched power optimizer 20 as the seventh solar cell module 12 including the ground fault position.

<Self-bias method>
Focusing on the vicinity of m=7, the power optimizers 20 with m=5 to 10 are in the Voc mode (about 50 V) and the power optimizers 20 with m=1 to 4 and m=11 to 14 are in the 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 voltage of the positive potential-negative potential of the solar cell string 10 is set to 100%, and the voltage (relative value) when the positive potential side is 0% and the negative potential side is 100%. In addition, the positive potential side voltage to ground V PG and the negative potential side voltage to ground V _NG of the solar cell string 10 are calculated based on the ground fault position near the negative potential side of the seventh solar cell module 12, which is known in advance, and the calculated value of V _PG /(V _PG +V _NG ) _, 50.1%, is shown by a dashed line.

At this time, the actual value of V _PG /(V _PG +V _NG ) based on the actual measured values of the positive potential side voltage to ground V _PG and the negative potential side voltage to ground V _NG of the solar cell string 10 was 50.4%, as shown by the solid line, which was in good agreement with the above-mentioned calculated value of 50.1%.

From this, as described above, it is understood that by calculating the ground fault bias V from the measured values of _VPG and _VNG and the following calculation formula of _VPG and _VNG using m=7 obtained by the Voc shift method, it is possible _to identify that a ground fault exists in the vicinity of the negative potential side of the m=7th solar cell module 12.
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G

(Verification 2)
A solar cell string 10 according to the first embodiment ( FIG. 3 ) was prepared in which 14 power optimizers 20 were connected in series and 14 solar cell modules 12 were connected in series. It was previously known that there were ground faults in this solar cell string 10 at two locations, namely, 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.

<Voc Shift Method>
All 14 power optimizers 20 were set to the low voltage mode (1 V), and the power optimizers 20 (m=2 to 13) were switched to the Voc mode (about 50 V) one by one in ascending order from the positive potential side. The results of measuring the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 at this time are shown in FIG.

As shown in Fig. 6, according to the Voc shift method, when _VPG and _VNG change significantly, the solar cell module 12 corresponding to the power optimizer 20 immediately preceding the switched power optimizer 20 can be narrowed down as the 12th solar cell module 12 including the ground fault position. However, the sixth solar cell module 12 including the ground fault position cannot be identified. Thus, when there are two or more ground faults, it is possible to accurately narrow down the position of one ground fault, but it is not possible to identify the other ground fault positions.

<Self-bias method>
First, focusing on the vicinity of m=12, if the power optimizers 20 with m=9 to 14 are in the Voc mode (about 50 V) and the power optimizers 20 with m=1 to 8 are in the 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 100%, and the voltage (relative value) when the positive potential side is 0% and the negative potential side is 100%. Also, based on the known ground fault position near the negative potential side of the 12th solar cell module 12, the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are calculated assuming a single point ground fault, and the calculated value of _VPG /( _VPG + _VNG ), 68.9%, is shown by a dashed line.

At this time, the actual value of _VPG /( _VPG + _VNG ) based on the actual measured values of the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 was 26.1%, as shown by the solid line, which differed by more than one Voc from the above-mentioned calculated value of 68.9%.

From this, as described above, when the ground bias V _G is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG using m=12 calculated by the Voc shift method, it is found that the difference is greater than one Voc.
V _PG = m x Vdc - V _G
V _NG =(M-m)×-Vdc-V _G

<Self-bias method>
Next, focusing on the vicinity of m=6, the power optimizers 20 with m=5 to 10 are set to the Voc mode (about 50 V) and the power optimizers 20 with m=1 to 4 and m=11 to 14 are set to the 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 set to 100%, and the voltage (relative value) when the positive potential side is set to 0% and the negative potential side is set to 100%. Also, based on the previously known ground-fault position near the negative potential side of the sixth solar cell module 12, the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are calculated assuming a single-point ground fault, and the calculated value of _VPG /( _VPG + _VNG ), 33.7%, is shown by a dashed line.

At this time, the actual value of _VPG /( _VPG + _VNG ) based on the actual measured values of the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 was 57.4%, as shown by the solid line, which differed from the above-mentioned calculated value of 33.7% by more than one Voc.

From this, as described above, when the ground bias V _G is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG using m=12 calculated by the Voc shift method, it is found that the difference is greater than one Voc.
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G

As described above, since the Voc shift method can accurately pinpoint the location of one of the two ground faults, it is possible to first perform maintenance on the m=12 solar cell modules 12 and their electrical circuits 16 based on the Voc shift method, and then perform the ground fault detection method again that combines the above-mentioned ground fault detection using the Voc shift method and the self-bias method. If two or more ground faults are still detected, it is possible to repeat the above-mentioned method.

(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.

<Voc Shift Method>
First, all of the M power optimizers 20 are set to a low voltage mode (e.g., 1 V). Next, the M power optimizers 20 are switched to a Voc mode (e.g., 50 V) one by one in descending order from the negative potential side of the solar cell string 10. At this time, the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

Since _VPG and _VNG change significantly before and after the power optimizer 20 in the Voc mode crosses the ground fault position, the m-th solar cell module 12 and its electric circuit 16 including the ground fault position are narrowed down based on the changes in _VPG and _VNG . In this modification, the input/output common battery of the power optimizer 20 is on the negative potential side, and the power optimizers 20 are switched to the Voc mode in descending order from the negative potential side of the solar cell string 10, so when _VPG and _VNG change significantly, 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 position.

3, when the third power optimizer 20 is switched to the Voc mode, _VPG and _VNG change by Voc as follows: This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the ground fault location.
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

4, even if a ground fault occurs near the positive potential side terminal of the third solar cell module 12, _VPG and _VNG change by Voc when the third power optimizer 20 is switched to the Voc mode as follows. 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

4, even if a ground fault occurs near the negative potential side terminal of the second solar cell module 12, _VPG and _VNG change by Voc when the second power optimizer 20 is switched to the Voc mode as follows. 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
_VPG =1V+1V- _VG
V _NG =-1V-1V-1V-Voc-V _G
m=2
_VPG =1V+Voc- _VG
V _NG =-1V-1V-1V-1V-V _G

<Self-bias method>
Next, all of the M power optimizers 20 are set to the low voltage mode (e.g., 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 (e.g., 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 voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

The ground fault bias V _G occurring on the input/output common potential side of the power optimizer 20 is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG .
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G

Then, the location of the ground fault in the solar cell string 10 is identified based on the obtained ground fault bias V _G. Specifically, if the obtained ground fault bias V _G is greater than 0 V and smaller than Voc (for one solar cell module), it is identified that the ground fault exists inside the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method. Furthermore, it is possible to identify which solar cell (or solar cell panel) in the solar cell module 12 has a ground fault from the magnitude of the obtained ground fault bias V _G.

On the other hand, if the determined ground 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.

If the obtained ground fault bias V _G is equal to or greater than Voc (for one solar cell module) or smaller than 0 V, it is determined that the narrowing down of the ground fault detection using the Voc shift method is incorrect, and it is determined that ground faults exist at two or more locations.

[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.

Figure 12 is a diagram showing the configuration of a power optimizer in the solar power generation system shown in Figure 11. The power optimizer 20 shown in Figure 12 differs from the power optimizer 20 of the first embodiment shown in Figure 2 in that the input and output common potentials are different. 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. 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 a common potential.

(Earth fault detection method)
Hereinafter, a method for detecting a ground fault in a photovoltaic power generation system according to the second embodiment, which is a method for detecting a ground fault in a photovoltaic string 10 by a ground fault detection device 32, will be described with reference to Fig. 13 and Fig. 14. Fig. 13 and Fig. 14 are diagrams showing a photovoltaic string in the photovoltaic power generation system shown in Fig. 11. Fig. 13 shows a form in which a ground fault exists inside the third photovoltaic module from the negative potential side, and Fig. 14 shows a form in which a ground fault exists near the negative potential side of the third photovoltaic module from the negative potential side, or near the positive potential side of the second PV module from the negative potential side.

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

<Voc Shift Method>
First, all of the M power optimizers 20 are set to a low voltage mode (e.g., 1 V). Next, the M power optimizers 20 are switched to a Voc mode (e.g., 50 V) one by one in ascending order from the negative potential side of the solar cell string 10. At this time, the positive potential side voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

Since _VPG and _VNG change significantly before and after the power optimizer 20 in the Voc mode crosses the ground fault position, the m-th solar cell module 12 and its electric circuit 16 including the ground fault position are narrowed down based on the changes in _VPG and _VNG . In the second embodiment, the input/output common potential of the power optimizer 20 is on 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, so when _VPG and _VNG change 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 position.

13, when the fourth power optimizer 20 is switched to the Voc mode, _VPG and _VNG change by Voc as follows: This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the ground fault location.
m=3
V _PG = 1V + 1V + 1V + V _G
V _NG =-1V-1V-Voc+V _G
m=4
_VPG =1V+1V+Voc+ _VG
V _NG =-1V-1V-1V+V _G

14, even if a ground fault occurs near the negative potential side terminal of the third solar cell module 12, _VPG and _VNG change by Voc when the fourth power optimizer 20 is switched to the Voc mode as follows, so that the third solar cell module 12 and its electric circuit 16, including the ground fault location, can be identified with high accuracy.
m=3
V _PG = 1V + 1V + 1V + V _G
V _NG =-1V-1V-Voc+V _G
m=4
_VPG =1V+1V+Voc+ _VG
V _NG =-1V-1V-1V+V _G

14 , even if a ground fault occurs near the positive potential side terminal of the second solar cell module 12, _VPG and _VNG change by Voc when the third power optimizer 20 is switched to the Voc mode as follows. 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
VNG =-1V-Voc+ _VG
m=3
V _PG = 1V + 1V + 1V + Voc + V _G
V _NG =-1V-1V+V _G

As a result, even if the ground fault is near the end of the solar cell module, the Voc shift method can accurately identify the mth solar cell module and its electrical 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 is located relative to the mth solar cell module and its electrical circuit. Therefore, the self-bias method is combined as follows.

<Self-bias method>
Next, all of the M power optimizers 20 are set to the low voltage mode (e.g., 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 (e.g., 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 voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

The ground fault bias V _G occurring on the input/output common potential side of the power optimizer 20 is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG .
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G

Then, the location of the ground fault in the solar cell string 10 is identified based on the obtained ground fault bias V _G. Specifically, if the obtained ground fault bias V _G is greater than 0 V and smaller than Voc (for one solar cell module), it is identified that the ground fault exists inside the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method. Furthermore, it is possible to identify which solar cell (or solar cell panel) in the solar cell module 12 has a ground fault from the magnitude of the obtained ground fault bias V _G.

On the other hand, if the determined ground 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.

If the obtained ground fault bias V _G is equal to or greater than Voc (for one solar cell module) or smaller than 0 V, it is determined that the narrowing down of the ground fault detection using the Voc shift method is incorrect, and it is determined that ground faults exist at two or more locations.

The earth fault detection device of the solar power generation system of the second embodiment and the method of detecting an earth fault in a solar cell string using the earth fault detection device can provide the same advantages as the earth fault detection device of the solar power generation system of the first embodiment and the method of detecting an earth fault in a solar cell string using the earth fault detection device.

(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.

<Voc Shift Method>
First, all of the M power optimizers 20 are set to a low voltage mode (e.g., 1 V). Next, the M power optimizers 20 are switched to a Voc mode (e.g., 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 voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

Since _VPG and _VNG change significantly before and after the power optimizer 20 in the Voc mode crosses the ground fault position, the m-th solar cell module 12 and its electric circuit 16 including the ground fault position are narrowed down based on the changes in _VPG and _VNG . 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, so when _VPG and _VNG change significantly, 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 position.

13, when the third power optimizer 20 is switched to the Voc mode, _VPG and _VNG change by Voc as follows: This makes it possible to accurately identify the third solar cell module 12 and its electric circuit 16, including the ground fault location.
m=4
_VPG =1V+1V+Voc+ _VG
V _NG =-1V-1V-1V+V _G
m=3
V _PG = 1V + 1V + 1V + V _G
V _NG =-1V-1V-Voc+V _G

14, even if a ground fault occurs near the negative potential side terminal of the third solar cell module 12, _VPG and _VNG change by Voc when the third power optimizer 20 is switched to the Voc mode as follows, so that the third solar cell module 12 and its electric circuit 16, including the ground fault location, can be identified with high accuracy.
m=4
_VPG =1V+1V+Voc+ _VG
V _NG =-1V-1V-1V+V _G
m=3
V _PG = 1V + 1V + 1V + V _G
V _NG =-1V-1V-Voc+V _G

14, even if a ground fault occurs near the positive potential side terminal of the second solar cell module 12, _VPG and _VNG change by Voc when the second power optimizer 20 is switched to the Voc mode as follows. 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
VNG =-1V-Voc+ _VG

<Self-bias method>
Next, all of the M power optimizers 20 are set to the low voltage mode (e.g., 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 (e.g., 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 voltage to ground _VPG and the negative potential side voltage to ground _VNG of the solar cell string 10 are measured.

The ground fault bias V _G occurring on the input/output common potential side of the power optimizer 20 is calculated from the measured values of V _PG and V _NG and the following calculation formula for V _PG and V _NG .
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G

Then, the location of the ground fault in the solar cell string 10 is identified based on the obtained ground fault bias V _G. Specifically, if the obtained ground fault bias V _G is greater than 0 V and smaller than Voc (for one solar cell module), it is identified that the ground fault exists inside the m-th solar cell module 12 narrowed down by the ground fault detection using the Voc shift method. Furthermore, it is possible to identify which solar cell (or solar cell panel) in the solar cell module 12 has a ground fault from the magnitude of the obtained ground fault bias V _G.

On the other hand, if the determined ground 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.

If the obtained ground fault bias V _G is equal to or greater than Voc (for one solar cell module) or smaller than 0 V, it is determined that the narrowing down of the ground fault detection using the Voc shift method is incorrect, and it is determined that ground faults exist at two or more locations.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment and various modifications and variations are possible.

Reference Signs List 1 Photovoltaic 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 generating unit 30 Power conditioner 32 Earth fault detection device

Claims (14)

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 lines 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. 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 . 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. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The solar power generation system according to any one of claims 1 to 3. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The solar power generation system according to any one of claims 1 to 3. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The solar power generation system according to any one of claims 1 to 3. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Voc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The solar power generation system according to any one of claims 1 to 3. 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 lines and
M power optimizers connected in series via the electric paths;
the M solar cell modules each corresponding to the M power optimizers in one-to-one correspondence 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. 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. 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. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = m x Vdc - V _G
V _NG =(M-m)×-Vdc-V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = m x Vdc - V _G
V _NG = (M-m)×-Vdc-V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Vdc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
The method for detecting a ground fault in a photovoltaic power generation system according to any one of claims 8 to 10. 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 earth fault bias V _{G is calculated from the following calculation formula for the positive potential side voltage to ground V PG} and the negative potential side voltage to ground V _NG of the solar cell string based on the calculated m, the output voltage Voc of the power optimizer, and the earth fault bias V _G occurring 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, where Vdc is Voc or a low voltage:
V _PG = (M-m) x Vdc + V _G
V _NG = m×-Vdc+V _G
Identifying a ground fault position of the solar cell string based on the determined ground fault bias V _G.
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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