Method for detecting insulation failures in solar power generation systems

Abstract

To provide an insulation failure detection method that can estimate the location of insulation failures. [Solution] An insulation failure detection method for a photovoltaic power generation system, which estimates the location of an insulation failure between a top cell connector and a bottom cell connector based on the voltage between the first top terminal and the second top terminal, the voltage between the first bottom terminal and the second bottom terminal, the voltage between the first top terminal and the first bottom terminal, and the voltage between the second top terminal and the second bottom terminal in an electrically floating state of the unit circuit, and in a state where the first top terminal and the first bottom terminal are connected and a variable resistor is connected in parallel with the top cell connector and the bottom cell connector whose potential difference does not rise when the first top terminal and the first bottom terminal are connected from the electrically floating state, and the resistance value of the variable resistor is adjusted so that no current flows between the first top terminal and the first bottom terminal, and the voltage between the first bottom terminal and the second bottom terminal.

Description

Technical Field

[0001] The present invention relates to an insulation failure detection method for a photovoltaic power generation system.

Background Art

[0002] In a photovoltaic power generation system including a large number of solar cells, the performance of some solar cells may deteriorate, and it is desired to identify the solar cells with deteriorated performance for replacement or disconnection from the system. For example, Patent Document 1 discloses a technique for identifying a deteriorated solar cell module based on an I-V characteristic obtained when the solar cell module is not shielded from light and an I-V characteristic obtained when the solar cell module is shielded from light, in a photovoltaic power generation system including a plurality of solar cell strings each formed by connecting a plurality of solar cell modules in series. A technique for identifying a deteriorated solar cell module based on the I-V characteristic in a state where the solar cell module is shielded from light has been proposed.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] If only the performance of one solar cell simply deteriorates, identification thereof is relatively easy, but various failures such as a short circuit between solar cells may occur. In order to improve photoelectric conversion efficiency, a top cell and a bottom cell having different absorption wavelengths are stacked, and in a tandem solar cell module, insulation failure (leakage) may occur between the top cell and the bottom cell. In a photovoltaic power generation system using a 4-terminal tandem solar cell module configured to output power independently from the top cell and the bottom cell respectively, it may be desired to identify the position where insulation failure between the top cell and the bottom cell has occurred. Therefore, an object of the present invention is to provide an insulation failure detection method for a photovoltaic power generation system that can estimate the position of an insulation failure between a top cell and a bottom cell. [Means for solving the problem]

[0005] (1) An insulation failure detection method for a photovoltaic power generation system according to one aspect of the present invention is an insulation failure detection method for detecting an insulation failure between a top cell connector and a bottom cell connector in a photovoltaic power generation system including a unit circuit comprising: a top cell connector having a plurality of top cells connected in series and a first top terminal and a second top terminal connected to the outside; and a bottom cell connector having a plurality of bottom cells connected in series and a first bottom terminal and a second bottom terminal connected to the outside, wherein the method detects an insulation failure between a top cell connector and a bottom cell connector in an electrical float state of the unit circuit, the measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, and the voltage between the first top terminal and the first bottom terminal Based on the measured values ​​of the first top terminal and the first bottom terminal, the measured voltage between the second top terminal and the second bottom terminal, and the measured voltage between the first top terminal and the second top terminal and between the first bottom terminal and the second bottom terminal to which the variable resistor is connected, with the first top terminal and the first bottom terminal connected and a variable resistor connected in parallel to the top cell connector and the bottom cell connector that does not cause a potential difference to rise when the first top terminal and the first bottom terminal are connected from an electrically floating state, and with the resistance value of the variable resistor adjusted so that no current flows between the first top terminal and the first bottom terminal, the location of the insulation failure between the top cell connector and the bottom cell connector is estimated.

[0006] (2) In the method for detecting insulation defects in a photovoltaic power generation system of (1), the resistance value between the top cell connector and the bottom cell connector may be further estimated based on the measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, and the measured current between the first top terminal and the first bottom terminal, when the first top terminal and the first bottom terminal are connected and the second top terminal and the second bottom terminal are open.

[0007] (3) In the method for detecting insulation failures in a photovoltaic power generation system according to (2), the unit circuit further includes a reverse current prevention diode between the plurality of top cells and the second top terminal or between the plurality of bottom cells and the second bottom terminal, whichever of the top cell connector and the bottom cell connector does not cause a potential difference to rise when the first top terminal and the first bottom terminal are connected from an electrically floating state, and the voltage between the first top terminal and the second top terminal or the voltage between the first bottom terminal and the second bottom terminal when the first top terminal and the first bottom terminal are connected is considered an equivalent voltage. Alternatively, the voltage between the first top terminal and the first bottom terminal and the voltage between the first bottom terminal and the second bottom terminal to which the variable resistor is connected may be measured when the first top terminal and the first bottom terminal are connected, the variable resistor is connected to the top cell connector or the bottom cell connector, and the resistance value of the variable resistor is adjusted to a value at which the current flowing between the first top terminal and the first bottom terminal transitions from a constant value to a decreasing value.

[0008] (4) In the method for detecting insulation defects in a photovoltaic power generation system according to (1) and (2), the unit circuit further has reverse current prevention diodes between the plurality of top cells and the second top terminal and between the plurality of bottom cells and the second bottom terminal, and the photovoltaic power generation system includes a plurality of the unit circuits connected in parallel with each other, and with the output terminal of the photovoltaic power generation system open and the first top terminal and first bottom terminal of the unit circuit connected, it may be determined whether or not an insulation defect exists in the unit circuit in question based on the change in current between the first top terminal and the first bottom terminal when a partial shade is formed over the unit circuit in question.

[0009] (5) In the method for detecting insulation defects in a photovoltaic power generation system according to (1) to (2), the photovoltaic power generation system includes a plurality of unit circuits connected in parallel with each other, and with the output terminal of the photovoltaic power generation system open and the first top terminal and first bottom terminal of the unit circuit connected, it may be determined whether or not an insulation defect exists in the unit circuit based on the measured value of the current output from each of the unit circuits.

[0010] (6) An insulation failure detection method for a photovoltaic power generation system according to another aspect of the present invention is an insulation failure detection method for detecting an insulation failure between a top cell connector and a bottom cell connector in a photovoltaic power generation system including a unit circuit comprising: a top cell connector having a plurality of top cells connected in series and a first top terminal and a second top terminal connected to the outside; and a bottom cell connector having a plurality of bottom cells connected in series and a first bottom terminal and a second bottom terminal connected to the outside, wherein the method estimates the resistance value between the top cell connector and the bottom cell connector based on the measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, the measured voltage between the first top terminal and the first bottom terminal, and the measured voltage between the second top terminal and the second bottom terminal in an electrically float state of the unit circuit, and the measured voltage between the first top terminal and the first bottom terminal, the measured voltage between the first bottom terminal and the second bottom terminal, and the measured current between the first top terminal and the first bottom terminal in a state where the first top terminal and the first bottom terminal are connected and the second top terminal and the second bottom terminal are open. [Effects of the Invention]

[0011] According to the present invention, a method for detecting insulation defects in a solar power generation system can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is a circuit diagram showing the configuration of a photovoltaic power generation system to which the insulation failure detection method according to the present invention can be applied. [Figure 2] This is a circuit diagram that models a unit circuit with an insulation defect. [Figure 3] This flowchart shows the procedure for the insulation failure detection method according to the first embodiment of the present invention. [Figure 4] Figure 3 is a circuit diagram illustrating the one-sided connection measurement process of the insulation failure detection method. [Figure 5] Figure 3 is a circuit diagram illustrating the variable resistor adjustment measurement process for the insulation failure detection method. [Figure 6] This is a circuit diagram showing the configuration of a photovoltaic power generation system that has a different unit circuit than Figure 3 to which the insulation failure detection method in Figure 3 is applied. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a circuit diagram showing the configuration of a photovoltaic power generation system 1 to which the insulation failure detection method according to the present invention can be applied. Figure 2 is a circuit diagram modeling a unit circuit 10 in the photovoltaic power generation system 1 where an insulation failure exists. Figure 3 is a flowchart showing the procedure of the insulation failure detection method according to one embodiment of the present invention.

[0014] The photovoltaic power generation system 1 in Figure 1 includes a plurality of 4-terminal tandem-type solar cell modules M, each stacked and sealed so that the top cells Ct and bottom cells Cb independently output power. The photovoltaic power generation system 1 includes a plurality of unit circuits 10 connected in parallel to each other, each comprising a top cell connector St having a plurality of top cells Ct connected in series and a first top terminal Tt1 and a second top terminal Tt2 connected to the outside, and a bottom cell connector Sb having a plurality of bottom cells Cb connected in series and a first bottom terminal Tb1 and a second bottom terminal Tb2 connected to the outside. Note that the insulation failure detection method according to the present invention can also be applied to a photovoltaic power generation system that includes only a single unit circuit 10.

[0015] A unit circuit 10 with an insulation fault can be modeled as shown in Figure 2. In the unit circuit 10, the insulation fault location between the top cell connector St and the bottom cell connector Sb is represented as a circuit with an insulation fault resistance Rs. The sets of top cells Ct before and after the insulation fault location of the top cell connector St are represented as the first top cell group St1 and the second top cell group St2, respectively, and the sets of bottom cells Cb before and after the insulation fault location of the bottom cell connector Sb are represented as the first bottom cell group Sb1 and the second bottom cell group Sb2, respectively. Furthermore, the connection fault point of the top cell connector St is represented as Pts, and the connection fault point of the bottom cell connector Sb is represented as Pbs.

[0016] The insulation failure detection method according to this embodiment, as shown in Figure 3, comprises a unit circuit identification step (step S1), a float measurement step (step S2), a one-sided connection measurement step (step S3), a variable resistance adjustment measurement step (step S4), and an insulation failure location estimation step (step S5). The insulation failure detection method according to the first embodiment of the present invention detects an insulation failure between the top cell connector St and the bottom cell connector Sb in a photovoltaic power generation system 1 and estimates the location where the insulation failure occurred. In cases where an insulation failure in a photovoltaic power generation system containing only a single unit circuit 10 is to be detected, the unit circuit identification step (step S1) can be omitted.

[0017] In step S1, the unit circuit identification step, it is determined whether or not an insulation defect exists in each unit circuit 10. In the unit circuit identification step, the output terminal of the photovoltaic power generation system 1 may be opened, and with the first top terminal Tt1 and the first bottom terminal Tb1 connected, the presence or absence of an insulation defect in each unit circuit 10 may be determined based on the measured value of the current output from each unit circuit 10. Since the absolute value of the current output from a unit circuit 10 with an insulation defect is larger than the absolute value of the current output from a unit circuit 10 without an insulation defect, the presence or absence of an insulation defect can be determined by comparing the output currents from the unit circuits 10. If multiple unit circuits 10 are connected in parallel with a reverse current prevention diode on the second top terminal Tt2 or second bottom terminal Tb2 side, the determination becomes easier because the output current is observed only from the unit circuit with the insulation defect. Note that if the only purpose is to check for the presence or absence of an insulation defect, it is not necessary to measure the exact current value, so the current output from the unit circuit 10 can be measured by clamping the output wiring of the unit circuit 10 in question with a clamp meter. Depending on the physical configuration of the photovoltaic power generation system 1, it may not be easy to directly measure the output current of the target unit circuit 10 with a clamp meter. In this case, the output current of the target unit circuit 10 may be calculated by the difference between the current flowing into the target unit circuit 10 from the upstream side and the current flowing out of the target unit circuit 10 to the downstream side. Furthermore, the current output from the unit circuit 10 may be represented by either the output current of the top cell connector St or the output current of the bottom cell connector Sb.

[0018] In the float measurement step S2, the following voltages are measured in the electrically float state of the unit circuit 10: V0(Tt2-Tt1) between the first top terminal Tt1 and the second top terminal Tt2, V0(Tb2-Tb1) between the first bottom terminal Tb1 and the second bottom terminal Tb2, V0(Tt1-Tb1) between the first top terminal Tt1 and the first bottom terminal Tb1, and V0(Tt2-Tb2) between the second top terminal Tt2 and the second bottom terminal Tb2. Note that if any three of these four voltages are measured, the remaining voltage can be calculated without actually measuring it.

[0019] In the one-side connection measurement step of step S3, as shown in FIG. 4, first, the first top terminal Tt1 and the first bottom terminal Tb1 are connected, and the second top terminal Tt2 and the second bottom terminal Tb2 are opened. Then, in this state, the voltage V1(Tt1-Tt2) between the first top terminal Tt1 and the second top terminal Tt2, the voltage V1(Tb2-Tb2) between the first bottom terminal Tb1 and the second bottom terminal Tb2, and the current Is between the first top terminal Tt1 and the first bottom terminal Tb1 are measured.

[0020] In the variable resistance adjustment measurement step of step S4, as shown in FIG. 5, first, the first top terminal Tt1 and the first bottom terminal Tb1 are connected, and a variable resistor Rv is connected in parallel with the one of the top cell connection body St and the bottom cell connection body Sb that does not have an increased potential difference when connecting the first top terminal Tt1 and the first bottom terminal Tb1 from an electrically floating state (the top cell connection body St in FIG. 5). Then, in a state where the resistance value of the variable resistor is adjusted such that no current flows between the first top terminal Tt1 and the first bottom terminal Tb1, the voltage V2(Tt2-Tt1) between the first top terminal Tt1 and the second top terminal Tt2, and the voltage V2(Tb2-Tb1) between the first bottom terminal Tb1 and the second bottom terminal Tb2 are measured.

[0021] In the insulation defect position estimation step of step S5, the position of an insulation defect between the top cell connection body St and the bottom cell connection body Sb is estimated based on the measured values obtained in the floating measurement step, the one-side connection measurement step, and the variable resistance adjustment measurement step. The estimation of the insulation defect position is described below.

[0022] When the measured value from the floating measurement step is decomposed into partial voltages, since Pts and Pbs are at the same potential in the floating state, it can be expressed as follows. V0(Tt2-Tt1)=V0(Tt2-Pts)+V0(Pts-Tt1)···(1) V0(Tb2-Tb1)=V0(Tb2-Pbs)+V0(Pbs-Tb1)···(2) V0(Tt1-Tb1)=V0(Pbs-Tb1)-V0(Pts-Tt1)...(3) V0(Tt2-Tb2)=V0(Tb2-Pbs)-V0(Tt2-Pts)...(4)

[0023] The following equation holds true for the measurement values ​​in the one-sided connection measurement process. Note that the voltages of the second top cell group St2 and the second bottom cell group Sb2, where no current flows, are the same as in the float measurement process, so substitute the voltages from the float measurement process. Is*Rs=V1(Pts-Tt1)-V1(Pbs-Tb1)...(5) V1(Tt2-Tt1)=V1(Pts-Tt1)+V0(Tt2-Pts)...(6) V1(Tb2-Tb1)=V1(Pbs-Tb1)+V0(Tb2-Pbs)...(7) V1(Pts-Pbs)=V1(Pts-Tt1)-V1(Pbs-Tb1)=V1(Tt2-Tt1)-V1(Tb2-Tb1)-V0(Tt2-Tb2)...(8)

[0024] In equation (8), V1(Tt2-Tt1), V1(Tb2-Tb1), and V0(Tt2-Tb2) are all measured voltages. Therefore, the value of the insulation failure resistance Rs at the insulation failure location can be calculated from equation (5), and the degree of insulation failure can be determined.

[0025] For the measured values ​​in the variable resistance adjustment measurement process, the following equation holds true using the ratio k of the operating voltage during measurement to the open-circuit voltage of the top cell connector St. Note that since no current flows between the first top terminal Tt1 and the first bottom terminal Tb1, no current flows through the insulation failure resistance Rs at the insulation failure location and the second bottom cell group Sb2, so the voltage of the second bottom cell group Sb2 is the same as in the float measurement process. V2(Pts-Tt1)=k*V0(Pts-Tt1)=V0(Pbs-Tb1)...(9)

[0026] From equations (3) and (9), V0(Pts-Tt1) and V0(Pbs-Tb1) can be calculated. Since the relationship between the position of the fault point Pts inside the top cell connector St in the floating state and the voltage is considered to be proportional, the position of the fault point Pts can be expressed as V0(Pts-Tt1) / V0(Tt2-Tt1), and similarly the position of the fault point Pbs in the bottom cell connector Sb can be expressed as V0(Pbs-Tb1) / V0(Tb2-Tb1). For this reason, the positions of the fault points Pts and Pbs can be estimated with high accuracy.

[0027] Furthermore, the insulation failure detection method according to the present invention can also be applied to a photovoltaic power generation system 1A, which has multiple unit circuits 10A as shown in Figure 6, and in which a unit circuit 10A cannot be easily isolated from other unit circuits 10A to be in a floating state. Each unit circuit 10A of the photovoltaic power generation system 1A further has reverse current prevention diodes Dt and Db between the top cell connector St and the second top terminal Tt2, and between the bottom cell connector Sb and the second bottom terminal Tb2. In the photovoltaic power generation system 1A, the multiple top cell connectors St and the multiple bottom cell connectors Sb are connected in parallel. Note that the polarity of the top cell connector St, the bottom cell connector Sb, and the reverse current prevention diode Db is not limited to the example shown, and the terminal adjacent to the reverse current prevention diodes Dt and Db is understood to be the second top terminal Tt2 or the second bottom terminal Tb2. In such a circuit configuration, if the unit circuit 10A for which the location of the insulation failure is to be estimated cannot be isolated from other unit circuits 10A, the location of the insulation failure can be estimated by using the method described below.

[0028] For the photovoltaic power generation system 1A shown in Figure 6, in the one-sided connection measurement step S3 in Figure 3, even if the unit circuit 10A cannot be physically disconnected, it is sufficient to create a state where the system is not affected by the unit circuit 10A connected in parallel, and measure V1(Tt1-Tt2), V1(Tb2-Tb2), and Is). Specifically, the voltage V1(Tt1-Tt2) between the first top terminal Tt1 and the second top terminal Tt2, the voltage V1(Tb2-Tb2) between the first bottom terminal Tb1 and the second bottom terminal Tb2, and the current Is between the first top terminal Tt1 and the first bottom terminal Tb1 are measured as voltage and current when the first top terminal Tt1 and the first bottom terminal Tb1 are connected, and a variable resistor Rv is connected to either the top cell connector St or the bottom cell connector Sb, whichever does not cause the potential difference to rise when the first top terminal Tt1 and the first bottom terminal Tb1 are connected from an electrically floating state, and the resistance value of the variable resistor Rv is adjusted to a value at which the current flowing between the first top terminal Tt1 and the first bottom terminal Tb1 transitions from a constant value to a decreasing value. By doing so, the output of the parallel-connected top cell connector St does not affect the value of the current flowing between the first top terminal Tt1 and the first bottom terminal Tb1, and the voltage across the reverse current prevention diode Db can be made virtually zero, allowing for accurate measurement of voltage and current in a one-sided connection state.

[0029] Thus, the insulation failure detection method according to the present invention can estimate the location of an insulation failure even in a photovoltaic power generation system 1A that has a reverse current prevention diode Db.

[0030] In the photovoltaic power generation system 1A, in the unit circuit identification step S1 of Figure 3, the output terminal of the photovoltaic power generation system 1 is opened, and with the first top terminal Tt1 and the first bottom terminal Tb1 of the unit circuit 10 connected via an ammeter, it may be determined whether or not an insulation fault exists in the target unit circuit 10 based on the change in current between the first top terminal Tt1 and the first bottom terminal Tb1 when a partial shade is formed over the target unit circuit 10. If there is no insulation fault, no current will flow when the output terminal of the photovoltaic power generation system 1 is opened, simply by connecting the first top terminal Tt1 and the first bottom terminal Tb1. If an insulation fault exists, a small current will flow, but even if a shade is formed over a unit circuit 10 that does not have an insulation fault, the state of the unit circuit 10 that has an insulation fault does not change due to the effect of the reverse current prevention diode Db, and the current between the first top terminal Tt1 and the first bottom terminal Tb1 changes only when a shade is formed over a unit circuit that has an insulation fault. In other words, when the current between the first top terminal Tt1 and the first bottom terminal Tb1 changes, it can be determined that there is an insulation fault in the unit circuit 10 where a shadow is formed. In order to confirm the change in current between the first top terminal Tt1 and the first bottom terminal Tb1, the shadow that is formed is such that it clearly changes the output of the unit circuit 10. Note that it is not necessary to connect the first top terminal Tt1 and the first bottom terminal Tb1 for each unit circuit 10; it is sufficient to connect the wiring that connects the first top terminal Tt1 and the wiring that connects the first bottom terminal Tb1 of multiple unit circuits 10.

[0031] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. For example, in the insulation failure detection method for a photovoltaic power generation system according to the present invention, the one-sided connection measurement step or the variable resistance adjustment measurement step may be omitted. Also, in the present invention, the entire unit circuit may constitute a single solar cell module, and in a photovoltaic power generation system having a plurality of unit circuits, at least one of the plurality of top cell connectors and the plurality of bottom cell connectors may be connected in series. [Explanation of symbols]

[0032] 1.1A Solar Power Generation System 10,10A unit circuit Cb bottom cell Ct Top Cell M 4-terminal tandem type solar cell module Sb bottom cell connector Sb1 First bottom cell group Sb2 Second Bottom Cell Group St top cell connector St1 First Top Cell Group St2 Second Top Cell Group Tb1 First bottom terminal Tb2 Second bottom terminal Tt1 First top terminal Tt2 Second top terminal Pts top cell connector connection failure point Pbs bottom cell connection fault points Rs (Insulation failure resistance) Rv variable resistor

Claims

1. An insulation failure detection method for detecting an insulation failure between a top cell connector and a bottom cell connector in a photovoltaic power generation system, the system comprising a unit circuit including a top cell connector having a plurality of top cells connected in series and a first top terminal and a second top terminal connected to the outside, and a bottom cell connector having a plurality of bottom cells connected in series and a first bottom terminal and a second bottom terminal connected to the outside, wherein the system detects an insulation failure between the top cell connector and the bottom cell connector. The measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, the measured voltage between the first top terminal and the first bottom terminal, and the measured voltage between the second top terminal and the second bottom terminal in the electrically floating state of the unit circuit, With the first top terminal and the first bottom terminal connected, and with a variable resistor connected in parallel to the top cell connector and the bottom cell connector that does not cause a potential difference to rise when the first top terminal and the first bottom terminal are connected from an electrically floating state, and with the resistance value of the variable resistor adjusted so that no current flows between the first top terminal and the first bottom terminal, the measured voltage between the first top terminal and the second top terminal and between the first bottom terminal and the second bottom terminal to which the variable resistor is connected, A method for detecting insulation failures in a photovoltaic power generation system, which estimates the location of the insulation failure between the top cell connector and the bottom cell connector based on the above.

2. An insulation failure detection method for a photovoltaic power generation system according to claim 1, further estimating the resistance value between the top cell connector and the bottom cell connector based on the measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, and the measured current between the first top terminal and the first bottom terminal, while the first top terminal and the first bottom terminal are connected and the second top terminal and the second bottom terminal are open.

3. The unit circuit further includes a reverse current prevention diode between the plurality of top cells and the second top terminal or between the plurality of bottom cells and the second bottom terminal, whichever of the top cell connector and the bottom cell connector does not cause a potential difference to rise when the first top terminal and the first bottom terminal are connected from an electrically floating state. A method for detecting insulation defects in a photovoltaic power generation system according to claim 2, wherein the voltage between the first top terminal and the second top terminal or the voltage between the first bottom terminal and the second bottom terminal in a state where the second top terminal and the second bottom terminal are open is measured, and the voltage between the first top terminal and the second top terminal or the voltage between the first bottom terminal and the second bottom terminal to which the variable resistor is connected is measured in a state where the first top terminal and the first bottom terminal are connected, the variable resistor is connected to the top cell connector or the bottom cell connector, and the resistance value of the variable resistor is adjusted to a value in which the current flowing between the first top terminal and the first bottom terminal transitions from a constant value to a decreasing value.

4. The photovoltaic power generation system includes a plurality of the unit circuits connected in parallel to each other, The unit circuit further includes reverse current prevention diodes between the plurality of top cells and the second top terminal, and between the plurality of bottom cells and the second bottom terminal, A method for detecting insulation defects in a solar power generation system according to claim 1 or 2, wherein the output terminal of the solar power generation system is opened, and the first top terminal and the first bottom terminal of the unit circuit are connected, and a partial shadow is formed on the unit circuit to be targeted, and it is determined whether or not an insulation defect exists in the unit circuit to be targeted based on the change in current between the first top terminal and the first bottom terminal.

5. The photovoltaic power generation system includes a plurality of the unit circuits connected in parallel to each other, A method for detecting insulation defects in a solar power generation system according to claim 1 or 2, wherein the output terminal of the solar power generation system is opened, and the first top terminal and the first bottom terminal of the unit circuit are connected, and it is determined whether or not an insulation defect exists in the unit circuit based on the measured value of the current output from each of the unit circuits.

6. An insulation failure detection method for detecting an insulation failure between a top cell connector and a bottom cell connector in a photovoltaic power generation system, the system comprising a unit circuit including a top cell connector having a plurality of top cells connected in series and a first top terminal and a second top terminal connected to the outside, and a bottom cell connector having a plurality of bottom cells connected in series and a first bottom terminal and a second bottom terminal connected to the outside, wherein the system detects an insulation failure between the top cell connector and the bottom cell connector. The measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, the measured voltage between the first top terminal and the first bottom terminal, and the measured voltage between the second top terminal and the second bottom terminal in the electrically floating state of the unit circuit, With the first top terminal and the first bottom terminal connected and the second top terminal and the second bottom terminal open, the measured voltage between the first top terminal and the second top terminal, the measured voltage between the first bottom terminal and the second bottom terminal, and the measured current between the first top terminal and the first bottom terminal, A method for detecting insulation failure in a photovoltaic power generation system, which estimates the resistance value between the top cell connector and the bottom cell connector based on the above.

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