JP2014011429A - Conduction failure detection device, conduction failure detection system, and conduction failure detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect conduction failure of a solar cell reliably while ensuring safety.SOLUTION: A conduction failure detection device 5 for detecting conduction failure of a solar cell in power generation state comprises: a constant current circuit 51 for controlling a current, flowing between the negative electrode and positive electrode of a solar cell, to have a specified current value; a voltage measurement unit 52 for measuring an open voltage, i.e., the potential difference between the negative electrode and positive electrode of a solar cell when they are in open state, and a voltage during constant current, i.e., the potential difference between the negative electrode and positive electrode of a solar cell when the current is controlled to have a specified value by the constant current circuit 51; and a control/determination unit 53 for determining conduction failure of a solar cell based on the difference of an open voltage measured by the voltage measurement unit 52 and the voltage during constant current.

Description

  The present invention relates to a conduction failure detection device, a conduction failure detection system, and a conduction failure detection method.

  As a method for diagnosing a failure of a solar cell that generates power using sunlight, for example, a failure diagnosis method described in Patent Document 1 is known. In the failure diagnosis method, the measurement signal waveform is applied to the solar cell, and the response signal waveform is compared with the measurement signal waveform, thereby specifying the failure position and the failure type of the solar cell.

  Moreover, as another method for diagnosing a failure of a solar cell, for example, a diagnostic method described in Patent Document 2 below is known. In the diagnostic method, a charged capacitor is connected to a measurement target portion excluding the blocking diode of the solar cell string and discharged, and the voltage and current of the measurement target portion are measured during discharge. Diagnose the failure of the measurement target part based on the change.

JP 2009-21341 A JP 2011-66320 A

  However, in the fault diagnosis method described in Patent Document 1, it is necessary to measure the response to signal injection at a high speed, which makes accurate measurement difficult, and the accuracy of fault diagnosis sometimes decreases. Moreover, in the diagnostic method described in Patent Document 2, a large current corresponding to the voltage of the capacitor instantaneously flows to the measurement target part when there is no defect in the measurement target part, causing the current measurement device to malfunction. There is a possibility, and it is not preferable in terms of safety during measurement. Although it is conceivable to reduce the capacitance of the capacitor in order to reduce the large current at the measurement target portion, in this case, since the measurement time of the IV characteristic cannot be made long, accurate measurement of the IV characteristic is possible. In some cases, the accuracy of failure diagnosis may be reduced.

  Therefore, the present invention has been made in view of such problems, and a conduction failure detection device and a conduction failure detection system capable of accurately and stably detecting a conduction failure of a solar cell while ensuring safety. It is another object of the present invention to provide a conduction failure detection method.

  In order to solve the above problems, a continuity failure detection device according to one aspect of the present invention is a continuity failure detection device that detects a continuity failure for a solar cell in a power generation state, and includes a negative electrode and a positive electrode of the solar cell. A current source that controls the current flowing between the negative voltage and the positive electrode of the solar cell when the negative electrode and the positive electrode of the solar cell are opened, and an open circuit voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell. A voltage measuring unit that measures a constant current voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell when controlled to a specified current, and an open-circuit voltage and a constant current voltage that are measured by the voltage measuring unit. And a determination unit that determines a continuity failure of the solar cell based on the difference.

  Alternatively, a continuity failure detection method according to another aspect of the present invention is a continuity failure detection method by a continuity failure detection device that detects a continuity failure for a solar cell in a power generation state, and includes a negative electrode and a positive electrode of the solar cell. A first voltage measurement step for measuring an open voltage, which is a potential difference between the negative electrode and the positive electrode of the solar cell when the is opened, and a current flowing between the negative electrode and the positive electrode of the solar cell is defined as a specified current value A second current measuring step for measuring a constant current voltage, which is a potential difference between the negative electrode and the positive electrode of the solar cell when controlled to a specified current by the current supplying step, A determination step of determining a continuity failure of the solar cell based on a difference between the open-circuit voltage measured by the first voltage measurement step and the constant-current voltage measured by the second voltage measurement step.

  According to such a continuity failure detection device or a continuity failure detection method, an open circuit voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell when the negative electrode and the positive electrode of the solar cell are opened. Measured. Further, a constant current voltage, which is a potential difference between the negative electrode and the positive electrode of the solar cell when the negative electrode and the positive electrode are controlled to a predetermined current, is measured. And the poor conduction of a solar cell is determined based on the difference between the measured open circuit voltage and the constant current voltage. Here, in general, when there is a conduction failure location inside the solar cell, when the solar cell generates power, the conduction failure location becomes a resistance, and the voltage drops significantly compared to when there is no conduction failure. Therefore, according to the continuity failure detection device or the continuity failure detection method described above, it is possible to reliably determine the continuity failure of the solar cell by detecting the difference between the open circuit voltage and the constant current voltage. In addition, by measuring the potential difference in a constant current state, there is little risk of flowing a large current through the solar cell, and there is no need to scan the IV characteristics as in the diagnostic method using a capacitor. As a result, it is possible to detect a continuity failure of the solar cell simply and accurately while ensuring safety during inspection.

  In the continuity failure detection device described above, the determination unit is configured such that the difference between the open-circuit voltage and the constant-current voltage measured when the current flowing through the solar cell is controlled to a specified current value is greater than the first threshold value. It is preferable to determine the continuity failure of the solar cell. By doing so, it is possible to detect a continuity failure of the solar cell with a simple process or circuit configuration by performing a binary determination of comparing the measured difference with a threshold value.

  In addition, the determination unit determines that the resistance value calculated from the difference between the open-circuit voltage and the constant-current voltage measured when the current flowing through the solar cell is controlled to a specified current value and the specified current value is a reference resistance value. It is also preferable to determine the poor continuity of the solar cell when it is larger than. In this case, since the resistance value is calculated to determine the continuity failure, the continuity failure of the solar cell can be detected in consideration of the secular change of the parasitic resistance in the solar cell.

  The determination unit determines whether the solar cell is in a power generation state based on a comparison result between a short-circuit current value measured when the solar cell is short-circuited and a specified value, and the solar cell is in a power generation state. It is also preferable to start the determination of poor continuity of the solar cell when it is determined as being. In general, when the solar cell is not generating enough power, the fluctuation of the open circuit voltage is large, while when the short circuit current value is sufficiently generating near the rated current value, regardless of some fluctuations in solar radiation, The open circuit voltage shows a relatively stable value. Therefore, with the above configuration, the detection process can be executed in a stable open-circuit voltage state, and the conduction failure of the solar cell can be detected more reliably.

  Alternatively, a conduction failure detection system according to another aspect of the present invention includes a solar cell string configured by connecting a plurality of solar cell modules in series and a load device connected to the solar cell string. A continuity failure detection system for detecting a continuity failure in a solar cell string in a power generation state for a switching unit that switches a connection between the solar cell string and a load device to a disconnected state, and a switching unit Using a solar cell string switched to the column state as a detection target string, a current source that controls the current flowing between the negative electrode and the positive electrode of the detection target string to a specified current value, and the negative electrode and the positive electrode of the detection target string are in an open state The open circuit voltage, which is the potential difference between the negative and positive electrodes of the detection target string, and the current source A voltage measurement unit that measures a constant current voltage that is a potential difference between the negative electrode and the positive electrode of the detection target string when controlled to a constant current, and an open-circuit voltage and a constant current voltage that are measured by the voltage measurement unit And a determination unit that determines a continuity failure in the detection target string based on the difference between.

  Alternatively, a conduction failure detection method according to another aspect of the present invention includes a solar cell string including a plurality of solar cell modules connected in series and a load device connected to the solar cell string. A continuity failure detection method by a continuity failure detection system for detecting a continuity failure in a solar cell string that is in a power generation state, and a step of switching a connection between the solar cell string and a load device to a disconnected state; An open circuit voltage that is a potential difference between the negative electrode and the positive electrode of the detection target string when the negative electrode and the positive electrode of the detection target string are opened using the solar cell string switched to the disconnected state by the switching step as the detection target string. A first voltage measurement step for measuring the negative electrode and the positive electrode of the string to be detected A current supply step for controlling the current flowing through the current to a specified current value, and a constant current voltage that is a potential difference between the negative electrode and the positive electrode of the detection target string when the current supply step is controlled to the specified current. A conduction failure in the detection target string is determined based on a difference between the second voltage measurement step and the open-circuit voltage measured by the first voltage measurement step and the constant current voltage measured by the second voltage measurement step. And a determination step.

  According to the continuity failure detection system or the continuity failure detection method, the potential difference between the negative electrode and the positive electrode of the solar cell string when the negative electrode and the positive electrode of the solar cell string are opened with respect to the solar cell string. The open circuit voltage is measured. Furthermore, a constant current voltage, which is a potential difference between the negative electrode and the positive electrode of the solar cell string when the negative electrode and the positive electrode are controlled to a predetermined current, is measured. Then, the poor conduction of the solar cell string is determined based on the difference between the measured open circuit voltage and the constant current voltage. Here, in general, when there is a poor conduction point in the solar cell string, when the solar cell string generates power, the poor conduction point becomes a resistance, and the voltage drops significantly compared to the case where there is no poor conduction. To do. Therefore, according to the continuity failure detection device or the continuity failure detection method described above, it is possible to reliably determine the continuity failure of the solar cell string by detecting the difference between the open circuit voltage and the constant current voltage. In addition, by measuring the potential difference in the constant current state, there is little risk of flowing a large current through the solar cell string, and there is no need to scan the IV characteristics as in the diagnostic method using a capacitor. Thereby, it is possible to detect a conduction failure of the solar cell string simply and accurately while ensuring safety at the time of inspection.

  According to the present invention, it is possible to reliably detect poor conduction of solar cells while ensuring safety.

It is a block diagram which shows the solar energy power generation system containing the conduction failure detection system which concerns on 1st Embodiment of this invention. It is a figure which shows the detailed structure of the solar cell string contained in the solar energy power generation system of FIG. It is a figure which shows the equivalent circuit of the photovoltaic cell of FIG. It is a graph which shows the current-voltage characteristic of the solar cell module of FIG. It is a graph which shows the current-voltage characteristic of the solar cell string of FIG. It is a graph which shows the current-voltage characteristic of the solar cell array of FIG. It is a block diagram which shows the solar power generation system containing the conduction | electrical_connection defect detection system which concerns on the modification of this invention.

  Hereinafter, embodiments of a conduction failure detection device, a conduction failure detection system, and a conduction failure detection method according to the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram of a solar power generation system according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a detailed configuration of a solar cell string included in the solar power generation system of FIG. A solar power generation system 1 shown in FIG. 1 is a power generation system that uses solar energy to generate power. For example, the solar power generation system 1 is installed in a high place such as a roof and has a grid connection type having an output voltage of 200 V or more. Has been. The solar power generation system 1 includes a solar cell array 100 and a power conditioner 110. Note that it is not necessary to limit to a grid-connected system, and an independent system independent (independent) from the power system may be used.

  The solar cell array 100 converts solar energy into electric energy and supplies it to the power conditioner 110 as a DC output. As shown in FIG. 2, the solar cell array 100 includes at least one solar cell string 130 in which a plurality of solar cell modules 120 are connected in series. Here, the solar cell array 100 is configured by connecting three solar cell strings 130 to each other in parallel. These solar cell strings 130 are connected to the power conditioner 110 via a switch of the continuity failure detection system 2 described later.

  The power conditioner 110 converts the direct current output supplied from the solar cell array 100 into an alternating current output, and supplies the alternating current output to an electric power system (for example, a commercial electric power system) connected to the load device at the subsequent stage. The power conditioner 110 has an operating voltage control function for controlling the operating voltage of the solar cell array 100 so that the maximum output of the solar cell array 100 can be obtained, and the system is safely stopped when an abnormality in the power system is detected. System protection function. The power conditioner 110 may be a transformer insulation type having an insulation transformer or a transformerless (non-insulation) type.

  The solar cell module 120 is configured in a panel shape, and includes a plurality (six in this case) of solar cells 140 connected in series with each other as shown in FIG. Moreover, the solar cell module 120 includes a bypass diode 150 connected in parallel to the plurality of solar cells 140 connected in series. That is, the anode terminal of the bypass diode 150 is connected to the negative electrode side of the solar cell module 120, and the cathode terminal of the bypass diode is connected to the positive electrode side of the solar cell module. A combination of a plurality of solar battery cells 140 connected in series to each other and a bypass diode 150 connected in parallel to the solar battery 140 group is referred to as a solar battery cluster. In the present embodiment, the solar cell module 120 is described as being configured from one solar cell cluster, but is not limited thereto, and may be configured to have a plurality of solar cell clusters connected in series with each other. good.

  The plurality of solar cells 140 generate power using sunlight, and are fixed to the aluminum frame in a state of being arranged in a matrix, and the light receiving surface side is covered with tempered glass. As the solar cell 140, for example, a crystalline solar cell having an output voltage of 0.5V is used.

  The bypass diode 150 is connected to the plurality of solar cells 140 in parallel. As the bypass diode 150, for example, a Schottky barrier diode is used in order to reduce the forward voltage and shorten the reverse recovery time. The bypass diode 150 is provided such that a current flows when a reverse voltage is applied to the solar cell module 120, and its forward direction is the forward direction of the equivalent parasitic diode of the solar cell 140 in the solar cell module 120. On the other hand, it is the opposite direction. Specifically, the cathode side of the bypass diode 150 is connected to the positive electrode side of the solar cell module 120 on the electric circuit connecting the solar cell modules 120 in series. The anode side of the bypass diode 150 is connected to the negative electrode side of the solar cell module 120 on the electric circuit.

  FIG. 3 shows an equivalent circuit diagram of the solar battery cell 140. As shown in the figure, the solar cell 140 can be considered equivalent to a parallel circuit of a current source 141, a parasitic diode 142, and a shunt resistor 143. That is, the solar battery cell 140 includes a current source 141 that generates a current corresponding to the solar radiation intensity between the negative electrode and the positive electrode inside the cell 140 (for example, from the negative electrode toward the positive electrode), and a positive electrode inside the cell 140. This is equivalent to a parasitic diode 142 having a forward direction from the negative electrode to the negative electrode and a shunt resistor 143 having a resistance value of several hundred to 1 kΩ (ideally infinite Ω). Further, when a current equal to or greater than the current generated by the current source 141 is generated in the solar cell 140 from the negative electrode to the positive electrode, the current flows through the shunt resistor 143.

  Returning to FIG. 1, the configuration of the continuity failure detection system 2 included in the photovoltaic power generation system 1 will be described. The continuity failure detection system 2 is a device group for detecting a continuity failure in the solar cell string 130 for the solar cell string 130 that is switched to a disconnected state with respect to the load device including the power conditioner 110. . Specifically, the continuity failure detection system 2 includes switch groups (switching units) 3 and 4 and a continuity failure detection device 5.

  The switch group 3 is provided to switch the connection between the three solar cell strings 130 and the power conditioner 110 to the disconnected state at the time of the continuity failure inspection, and has six switching elements 31A and 31B corresponding to the number of the solar cell strings 130. , 32A, 32B, 33A, 33B. The switching elements 31 </ b> A, 31 </ b> B, 32 </ b> A, 32 </ b> B, 33 </ b> A, 33 </ b> B are switches that control the electrical connection between the solar cell string 130 and the power conditioner 110. As the switching elements 31A, 31B, 32A, 32B, 33A, and 33B, any configuration can be used as long as the current is interrupted. For example, an FET (Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), or the like. An electromagnetic switch such as a semiconductor switch or a mechanical relay can be used. The switching elements 31A, 31B, 32A, 32B, 33A, and 33B are closed during normal time (during power generation), and connect the solar cell string 130 and the power conditioner 110 to each other, while being open during continuity check. And let them be disconnected from each other.

  Specifically, the switching elements 31A, 32A, and 33A are provided on an electric circuit that connects between the positive electrode of each solar cell string 130 and one input terminal of the power conditioner 110, and the switching elements 31B, 32B, and 33B. Is provided on an electric circuit that connects between the negative electrode of each solar cell string 130 and the other input terminal of the power conditioner 110. In addition, although the switch group 3 is provided on both electric circuits connected to the positive electrode and the negative electrode of the solar cell string 130, it may be provided only on one of the electric circuits. For example, the switch group 3 may be composed of only the switching elements 31A, 32A, and 33A. Even with such a configuration, the solar cell string 130 and the power conditioner 110 can be disconnected from each other during the continuity failure inspection.

  The switch group 4 is provided to electrically connect the three solar cell strings 130 and the continuity failure detection device 5 at the time of the continuity failure inspection, and includes six switching elements corresponding to the number of the solar cell strings 130. 41A, 41B, 42A, 42B, 43A, 43B. The switching elements 41A, 41B, 42A, 42B, 43A, and 43B are switches that control the electrical connection between the solar cell string 130 and the continuity failure detection device 5, and are the same semiconductor switches and electromagnetic switches as the switch group 3 Etc. can be adopted. The switching elements 41A, 41B, 42A, 42B, 43A, and 43B are normally opened (during power generation), and the continuity failure detection device 5 is electrically disconnected from the solar cell string 130, while the continuity failure is present. At the time of inspection, they are closed and are connected to each other.

  Specifically, the switching elements 41A, 42A, 43A are provided on an electric circuit that connects between the positive electrode of each solar cell string 130 and one connection terminal of the continuity failure detection device 5, and the switching elements 41B, 42B, 43B is provided on an electric circuit that connects between the negative electrode of each solar cell string 130 and the other connection terminal of the continuity failure detection device 5. In addition, although the switch group 4 is provided on both the electric circuits connected to the positive electrode and the negative electrode of the solar cell string 130, it may be provided only on one of the electric circuits. For example, the switch group 4 may be configured only from the switching elements 41A, 42A, and 43A. Even with such a configuration, the solar cell string 130 and the continuity failure detection device 5 can be disconnected from each other at normal times.

  A backflow prevention diode (not shown) that prevents a reverse current from flowing through the solar cell string 130 is provided between the solar cell string 130 and the power conditioner 110. (Both poles) are connected in series on the electric circuit. The backflow prevention diode may be configured to be located in the electric circuit to be measured by the continuity failure detection device 5, or may be configured to be located outside the electric circuit to be measured. In other words, regardless of the position of the switch group 3 or the position of the connection point 6 with the continuity failure detection device 5, it can be located anywhere on the electric circuit connecting the positive electrode (or negative electrode) of the solar cell string and the power conditioner 110. Good (however, it is necessary to be located closer to the solar cell string 130 than the parallel connection point with other solar cell strings 130).

  The continuity failure detection device 5 includes a constant current circuit 51, a voltage measurement unit 52, a control / determination unit 53, and a switch 54. The constant current circuit 51 is a circuit that controls the current flowing in the detection target string 130 to a specified constant current value by changing the resistance (or internal resistance) regardless of the power generation state of the connected solar cell string 130. These terminals are connectable to the positive and negative electrodes of the three solar cell strings 130 via the switching elements 41A, 42A, 43A and the switching elements 41B, 42B, 43B, respectively. As the constant current circuit 51, any configuration can be used as long as the current is controlled to a constant current. For example, the constant current circuit 51 can be configured by an electric circuit using an operational amplifier, a transistor, a constant current diode, or the like. . Here, the current value of the current generated by the constant current circuit 51 can be adjusted according to an instruction signal from the control / determination unit 53. With such a constant current circuit 51, the current flowing between the negative electrode and the positive electrode (for example, from the negative electrode to the positive electrode) is controlled to a specified current value for any of the three solar cell strings 130.

  Note that a switch 54 is connected in series to the constant current circuit 51, and the constant current circuit 51 can be connected to or disconnected from the solar cell string 130 connected for inspection. That is, the constant current circuit 51 is disconnected from the detection target string 130 by opening the switch 54 so that the open voltage can be measured, and the constant current circuit 51 is detected by setting the switch 54 closed. Connect to a constant current.

  The voltage measuring unit 52 is a circuit unit for measuring a potential difference between the negative electrode and the positive electrode of the solar cell string 130, and both terminals thereof are respectively switching elements 41A, 42A, 43A and switching elements 41B, 42B, It is possible to connect to the positive and negative electrodes of the three solar cell strings 130 via 43B. Here, the measurement timing of the potential difference by the voltage measurement unit 52 can be controlled by the control / determination unit 53, and a signal indicating the potential difference measured by the voltage measurement unit 52 can be acquired by the control / determination unit 53. Has been. Such a voltage measurement unit 52 measures the potential difference in any of the three solar cell strings 130. Specifically, the voltage measuring unit 52 measures an open voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell string 130 when the negative electrode and the positive electrode of the solar cell string 130 are opened. Further, the voltage measuring unit 52 specifically measures a constant current voltage which is a potential difference between the negative electrode and the positive electrode of the solar cell string 130 when the current is controlled to a specified value by the constant current circuit 51.

  The control / determination unit 53 performs control so as to switch the open / close state of the switch groups 3 and 4 during the continuity failure inspection, and a voltage change that is a difference between the open-circuit voltage measured by the voltage measurement unit 52 and the constant-current voltage. Get the value. Then, the control / determination unit 53 detects a conduction failure in any of the solar cell strings 130 based on the acquired voltage change value, and outputs a detection result. Such a control / determination unit 53 may be configured by a circuit unit such as an analog circuit or a digital circuit, or may be configured by an information processing apparatus such as a microcomputer.

  Here, before describing the details of the function of the control / determination unit 53, current-voltage characteristics (hereinafter referred to as “IV characteristics”) when the solar cell module 120 and the solar cell string 130 are normal and defective in conduction. Will be described.

  FIG. 4 is a graph showing the IV characteristics of the solar cell module 120 (that is, one solar cell cluster) during the daytime (during power generation). In the same figure, L1 shows the IV characteristic of the solar cell module 120 with no poor conduction, and L2 shows the IV characteristic of the solar cell module 120 with poor conduction. In these characteristics, a positive voltage (V> 0) is indicated when the potential of the positive electrode of the solar cell module 120 is higher than the potential of the negative electrode, and the current from the negative electrode to the positive electrode is positive in the solar cell module 120. Current (I> 0) is shown.

  During the daytime (during power generation), the open circuit voltage does not change unless there is a complete disconnection even if there is a poor conduction point in the solar cell module 120. However, when current is passed through the solar cell module 120, if the continuity in the solar cell module 120 is normal, the voltage drops according to the characteristics of the normal solar cell as shown in the characteristic L1 of FIG. If there is a conduction failure in the solar cell module 120, the conduction failure portion becomes a resistance, and the voltage is remarkably lowered as shown by the characteristic L2 in FIG. Note that as the current is increased, the voltage of the solar cell module 120 including the conduction failure portion drops to 0V. However, even if the current is increased further, the bypass diode 150 is activated, and therefore, it does not fall below 0 V (more precisely, the voltage drop due to the bypass diode 150).

FIG. 5A is a graph showing the IV characteristics of the solar cell string 130 during the daytime (during power generation). The graph shown in FIG. 5A is obtained by serially synthesizing the IV characteristics of the solar cell modules 120 included in the solar cell string 130. In the same figure, L1 has shown the IV characteristic of the solar cell string 130 when there is no conduction defect. L2 indicates the IV characteristic of the solar cell string 130 when there is a conduction failure inside any of the solar cell clusters included in the solar cell string 130 (for example, the position 300 shown in FIG. 2). As shown in FIG. 5A, during the daytime (during power generation), the open circuit voltage V _OC does not change unless there is a complete disconnection, regardless of whether or not there is a poor conduction point in the solar cell string 130. However, the solar cell string 130, that which causes a slight current I ₁ as compared to the short-circuit current of the solar cell string 130, if the normal conduction of the solar cell string 130, the characteristics of FIG. 5 (a) L1 As shown in FIG. 5A, the voltage hardly decreases according to the characteristics of a normal solar cell. On the other hand, if there is a conduction failure in the solar cell string 130, the conduction failure location becomes a resistance. Compared with the characteristic L1, the voltage drops significantly (ΔV).

FIG. 5B is an enlarged view of the graph in the vicinity of the open circuit voltage V _{OC in} the graph shown in FIG. As shown in FIG. 5 (b), a voltage at a current _{I 1} in the characteristic L1 _{V 1,} the difference between the open circuit voltage _{V OC} and _{V 1} [Delta] V _1, at a current _{I 1} in the characteristic L2 The voltage is V ₂ , and the difference between the open circuit voltages V _OC and V ₂ is ΔV ₂ . As shown in FIG. 5B, when the current I ₁ is passed through the solar cell string 130, the voltage decreases by ΔV _{1 in} the characteristic L1, whereas the voltage decreases by ΔV ₂ that is much larger than ΔV _{1 in the} characteristic L2. To do.

FIG. 6 is a graph showing the IV characteristics of the solar cell string 130 during the daytime (during power generation). In the same figure, L1 is the IV characteristic of the solar cell string 130 with no conduction failure, and L2 is the sun with conduction failure outside the solar cell cluster included in the solar cell string 130 (for example, the position 301 shown in FIG. 2). The IV characteristic of the battery string 130 is shown. Similar to the case of FIG. 5, when the current I ₁ is passed through the solar cell string 130, the voltage in the characteristic L 2 is significantly reduced compared to the characteristic L 1 (ΔV). Therefore, the continuity failure detection system 2 and the continuity failure detection method using the same also detect the continuity failure in the solar cell string 130 (when there is a continuity failure outside the solar cell cluster included in the solar cell string 130). be able to.

  Using the above-described IV characteristics of the solar cell string, the control / determination unit 53 determines the conduction failure of the solar cell string 130. Specifically, the control / determination unit 53 controls the switch group 3 so that the gap between any one of the solar cell strings 130 to be inspected (hereinafter also referred to as detection target strings) and the power conditioner 110. At the same time as setting the disconnected state, the switch group 4 is controlled to connect the detection target string 130 to the constant current circuit 51 and the voltage measuring unit 52 of the continuity failure detection device 5. For example, the control / determination unit 53 controls the pair of switching elements 31A and 31B, the pair of switching elements 32A and 32B, or the pair of switching elements 33A and 33B to be in an open state, and correspondingly The pair of switching elements 41A and 41B, the pair of switching elements 42A and 42B, or the pair of switching elements 43A and 43B is controlled to be closed.

In this state, the control / determination unit 53 first opens the switch 54 to disconnect the constant current circuit 51 to open the detection target string 130 and then controls the voltage measurement unit 52 to control the detection target string 130. The open circuit voltage V _OC which is a potential difference between the negative electrode and the positive electrode is measured. Next, the control / determination unit 53 closes the switch 54 and connects the constant current circuit 51 to the detection target string 130, and then the constant current circuit 51 causes the current I between the negative electrode and the positive electrode of the detection target string 130. ₁ constant current flows. Then, the control / determination unit 53 controls the voltage measurement unit 52 so that the constant-current voltage is a potential difference between the negative electrode and the positive electrode of the detection target string 130 when the constant current circuit 51 suppresses the current I _1. To measure. Further, the control / determination unit 53 calculates a voltage change value ΔV, which is a difference between the open-circuit voltage V _OC of the detection target string 130 measured by the voltage measurement unit 52 and the constant current voltage, and the voltage change value ΔV is defined. It is determined whether or not the threshold value V _TH0 is greater than the threshold value V _TH0 , and if the voltage change value ΔV is greater than the threshold value V _TH0 , the conduction failure of the detection target string 130 is detected. By such a function of the control / determination unit 53, it is possible to determine whether the IV characteristic of the detection target string 130 is the characteristic L1 or L2 shown in FIG. 5, and the IV characteristic is the characteristic. When it is determined that it is L2, a conduction failure can be detected.

In the present invention, a solar cell string with a good conduction state behaves close to a voltage source near a current of 0, and a slight current change hardly changes the voltage, but a conduction failure occurs and the series resistance Rs increases. The solar cell string utilizes the characteristic that a voltage drop of ΔI × Rs occurs due to a slight current change (ΔI) from around current 0. Therefore, when the current value I ₁ (that is, the increment from the value of the current 0) is set to a value close to the short-circuit current I _SC or the maximum output operating point current I _pm of the detection target string 130, the solar cell having a good conduction state Even a string does not behave like a voltage source and cannot be detected normally. Further, the current value I ₁ is too small, the voltage change value ΔV small, detection is unreliable.

  Next, a continuity failure inspection procedure for the above-described photovoltaic power generation system 1 will be described, and a continuity failure detection method according to the present embodiment will be described in detail.

  First, the switch groups 3 and 4 are controlled by the control / determination unit 53 of the continuity failure detecting device 5 and at the same time the disconnection state is set between any one of the detection target strings 130 and the power conditioner 110. The detection target string 130 and the continuity failure detection device 5 are connected (first switching step). Here, when set to the disconnected state, both poles of the detection target string 130 may be cut, or only the direction pole side of the detection target string 130 may be cut.

Next, the open-circuit voltage V _OC of the detection target string 130 is measured by the voltage measurement unit 52 (first voltage measurement step). Thereafter, the constant current circuit 51 of the continuity failure detection device 5 is controlled so that the current I ₁ flows between the negative electrode and the positive electrode (for example, from the negative electrode to the positive electrode) with respect to the detection target string 130 (current control). Step). At this timing, the voltage measurement unit 52 measures the constant-current voltage of the detection target string 130 and passes the measurement value to the control / determination unit 53 (second voltage measurement step). On the other hand, the voltage change value ΔV, which is the difference between the open-circuit voltage V _OC measured in the first voltage measurement step and the constant current voltage measured in the second voltage measurement step by the control / determination unit 53. Is calculated, and it is determined whether or not the voltage change value ΔV is larger than a prescribed threshold value V _{TH0, and} a conduction failure of the detection target string 130 is detected based on the determination result (determination step). Then, the control / determination unit 53 outputs the detection result to an output device such as a display or an LED (output step). Finally, when a continuity failure is not detected, the control / determination unit 53 controls the switch groups 3 and 4 to release the connection between the detection target string 130 and the continuity failure detection device 5. At the same time, a connection state is set between the detection target string 130 and the power conditioner 110 (second switching step).

According to the continuity failure detection system 2 described above and the continuity failure detection method using the same, the negative electrode of the solar cell string 130 when the negative electrode and the positive electrode of the solar cell string 130 are opened with respect to the solar cell string 130. An open circuit voltage V _OC, which is a potential difference between the positive electrode and the positive electrode, is measured. Further, a constant current voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell string 130 when the current is controlled to a predetermined current value between the negative electrode and the positive electrode (for example, from the negative electrode to the positive electrode). Is measured. Then, based on the difference ΔV between the measured open circuit voltage and constant current voltage, the conduction failure of the solar cell string 130 is determined. Here, in general, when there is a conduction failure location inside the solar cell string 130, when the solar cell string 130 generates power, the conduction failure location becomes a resistance, and the voltage is significantly higher than when there is no conduction failure. Falls. Therefore, according to the conduction failure detection system 2 or the conduction failure detection method described above, the conduction failure of the solar cell string 130 can be reliably determined by detecting the difference between the open circuit voltage and the constant current voltage. . In addition, by measuring the potential difference in the constant current state, there is little possibility of a large current flowing through the solar cell string 130, and there is no need to scan the IV characteristics as in the conventional diagnostic method using a capacitor. Thereby, the conduction | electrical_connection defect of the solar cell string 130 can be detected easily and correctly, ensuring the safety | security at the time of a test | inspection.

In the continuity failure detection system 2 described above, the control / determination unit 53 determines the difference ΔV between the open-circuit voltage V _OC and the constant current voltage measured when the current flowing through the solar cell string 130 is controlled to the specified current I _1. However, the conduction failure of the solar cell string 130 may be determined when it is larger than the threshold value V _TH0 . By doing so, it is possible to detect a conduction failure of the solar cell string 130 with simple processing and circuit configuration by performing a binary determination of comparing the measured difference ΔV with the threshold value V _TH0 .

  In addition, this invention is not limited to embodiment mentioned above.

For example, the control / determination unit 53 has a resistance value calculated from the difference between the open-circuit voltage and the constant-current voltage measured when the current flowing through the solar cell string 130 is set to the specified current I ₁ and the current I _1. When the resistance value is larger than the reference resistance value, the conduction failure of the solar cell string 130 may be determined. In this case, since the resistance value is calculated to determine the continuity failure, the continuity failure of the solar cell can be detected in consideration of the secular change of the parasitic resistance in the solar cell.

The control / determination unit 53 may determine whether or not the detection target string 130 is in the power generation state when determining the start timing of the continuity failure inspection process. FIG. 7 shows a configuration of a continuity failure detection system 202 according to a modification of the present invention in this case. As shown in the figure, the continuity failure detection device 205 of the continuity failure detection system 202 is further provided with a current measurement unit 551 and a switch 552 for measuring a short-circuit current value when the detection target string 130 is short-circuited. ing. The current measurement unit 551 is configured to be connectable to the negative electrode and the positive electrode of the detection target string 130 via the switch group 4. The switch 552 is a switch for short-circuiting the detection target string 130 including the current measuring unit 551, and is open except when the short-circuit current is measured. The control / determination unit 253 closes the switch 552 immediately after the first switching step, acquires the short-circuit current value measured by the current measurement unit 54, and compares the short-circuit current value with a specified value. Thus, it is determined whether or not the detection target string 130 is in the power generation state. If the detection target string 130 is in the power generation state, the conduction failure inspection process for the solar cell string 130 is started. For example, the control / determination unit 253 determines that the detection target string 130 is in the power generation state when the measured short-circuit current value is larger than a specified value. Alternatively, the control / judging unit 253, the detection object string 130 based on the constant current value I ₁ ratio measured short-circuit current value may determine whether the power generating state. For example, if I _SC / I ₁ > α, it may be determined that power is being generated (daytime). The method for determining whether or not the detection target string 130 is generating power is not limited to the configuration illustrated in FIG. 7, and may be configured to determine whether or not the power generation is being performed by detecting illuminance with a pyranometer, It is good also as a structure which incorporates a time measuring function and determines whether it is generating electric power according to time.

  In the above embodiment, the case where the failure detection device 5 is a stationary type, the detection target string is extracted according to the control of the control / determination unit 53, and the continuity failure detection is performed has been described. Only the detection device 5 may be prepared as an independent portable device, and connected to a solar cell string, a solar cell module, or a solar cell cluster to be individually inspected.

  DESCRIPTION OF SYMBOLS 1 ... Solar power generation system (solar cell system), 2,202 ... Conduction failure detection system, 3 ... Switch group (switching part), 5,205 ... Conduction failure detection apparatus, 51 ... Constant current circuit, 52 ... Voltage measurement part 53, 253 ... control / determination unit, 54 ... switch, 61-66 ... connection point, 100 ... solar cell array, 110 ... power conditioner (load device), 120 ... solar cell module, 140 ... solar cell, 150 ... Bypass diode, 300, 301 ... Location of poor conduction, 551 ... Current measuring unit, 552 ... Switch.

Claims (7)

A continuity failure detection device that detects a continuity failure for a solar cell in a power generation state,
A current source for controlling the current flowing between the negative electrode and the positive electrode of the solar cell to a specified current value;
An open circuit voltage that is a potential difference between the negative electrode and the positive electrode of the solar cell when the negative electrode and the positive electrode of the solar cell are opened, and a negative electrode of the solar cell when the current source is controlled to a specified current A voltage measuring unit that measures a constant current voltage that is a potential difference between the positive electrode and the positive electrode;
A determination unit for determining a conduction failure of the solar cell based on a difference between the open-circuit voltage and the constant-current voltage measured by the voltage measurement unit;
A continuity failure detection device comprising: When the difference between the open-circuit voltage and the constant-current voltage measured when the current flowing in the solar cell is controlled to the specified current value is greater than a first threshold, the determination unit To determine the continuity of
The continuity failure detection device according to claim 1. The determination unit has a resistance value calculated from the difference between the open-circuit voltage and the constant-current voltage measured when the current flowing through the solar cell is controlled to the specified current value, and the specified current value. Determining a poor conduction of the solar cell when greater than a reference resistance value,
The continuity failure detection device according to claim 1. The determination unit determines whether the solar cell is in a power generation state based on a comparison result between a short-circuit current value measured when the solar cell is short-circuited and a specified value. When it is determined that the power generation state, the determination of the continuity failure of the solar cell,
The continuity failure detection device according to any one of claims 1 to 3. A solar cell system comprising a solar cell string configured by connecting a plurality of solar cell modules in series, and a load device connected to the solar cell string, in the solar cell string in a power generation state A continuity failure detection system for detecting a continuity failure,
A switching unit that switches the connection between the solar cell string and the load device to a disconnected state;
A current source that controls the current flowing between the negative electrode and the positive electrode of the detection target string to a specified current value using the solar cell string switched to the disconnected state by the switching unit as a detection target string,
Open circuit voltage that is a potential difference between the negative electrode and the positive electrode of the detection target string when the negative electrode and the positive electrode of the detection target string are opened, and the detection target when the current source is controlled to a specified current A voltage measurement unit that measures a constant current voltage that is a potential difference between the negative electrode and the positive electrode of the string;
A determination unit that determines a conduction failure in the detection target string based on a difference between the open circuit voltage measured by the voltage measurement unit and the constant current voltage;
A continuity failure detection system comprising: A continuity failure detection method by a continuity failure detection device that detects a continuity failure for a solar cell in a power generation state,
A first voltage measurement step of measuring an open voltage, which is a potential difference between the negative electrode and the positive electrode of the solar cell when the negative electrode and the positive electrode of the solar cell are in an open state;
A current supply step for controlling a current flowing between the negative electrode and the positive electrode of the solar cell to a specified current value;
A second voltage measuring step for measuring a constant current voltage which is a potential difference between the negative electrode and the positive electrode of the solar cell when controlled to a specified current by the current supply step;
A determination step of determining a conduction failure of the solar cell based on a difference between the open-circuit voltage measured by the first voltage measurement step and the constant-current voltage measured by the second voltage measurement step;
A continuity failure detection method comprising: A solar cell system comprising a solar cell string configured by connecting a plurality of solar cell modules in series, and a load device connected to the solar cell string, in the solar cell string in a power generation state A conduction failure detection method by a conduction failure detection system for detecting a conduction failure,
A switching step of switching the connection between the solar cell string and the load device to a disconnected state;
With the solar cell string switched to the disconnected state by the switching step as a detection target string, the potential difference between the negative electrode and the positive electrode of the detection target string when the negative electrode and the positive electrode of the detection target string are opened. A first voltage measuring step for measuring a certain open circuit voltage;
A current supply step of controlling a current flowing between the negative electrode and the positive electrode of the detection target string to a specified current value;
A second voltage measuring step for measuring a constant current voltage which is a potential difference between the negative electrode and the positive electrode of the detection target string when the current supply step is controlled to a specified current;
A determination step of determining a continuity failure in the detection target string based on a difference between the open circuit voltage measured in the first voltage measurement step and the constant current voltage measured in the second voltage measurement step. When,
A continuity failure detection method comprising:

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