JP6310948B2 - Solar cell inspection system and solar cell inspection method - Google Patents

Description

  The present invention relates to a technology for photovoltaic power generation, and more particularly to a technology effective when applied to a solar cell inspection system and a solar cell inspection method for detecting a failure of a solar cell module or a string.

  In recent years, with the introduction of FIT (Feed-in Tariffs), the market for large-scale photovoltaic power generation systems such as so-called mega solar with an output of 1 megawatt or more has expanded. In the mega solar system, several hundred to several tens of thousands of 100 W to 200 W class solar cell modules are arranged at one power generation site.

  As a method for detecting the failure of the solar cell module, for example, in addition to a method for inspecting cell deterioration visually, a method for detecting the presence or absence of abnormal heat generation of the cell with a thermometer, etc. A technique for inspecting electrical characteristics such as current-voltage characteristics of a solar cell string to be configured is employed. However, since the data measured outdoors where the solar cell module is installed is affected by changes in parameters such as the amount of solar radiation and temperature, it may be difficult to determine whether the inspection result is normal.

  As a technique related to this, for example, Japanese Patent No. 5162737 (Patent Document 1) discloses a measurement unit that measures a current-voltage characteristic of a solar cell and the current-voltage characteristic measured by the measurement unit. Each of the conversion unit for converting to the reference state, a memory for storing a plurality of reference characteristics, the current-voltage characteristic converted to the reference state, and each of the reference characteristics read from the storage unit, A solar cell characteristic evaluation apparatus including a determination unit that determines which of the reference characteristics the current-voltage characteristic is closest to is described.

Japanese Patent No. 5162737

In the technique described in Patent Document 1, the measured current-voltage characteristics are calculated based on JIS-C8913 by using R _s (series resistance [Ω]), K (curve correction factor), α (current temperature coefficient [A / ° C]), β (voltage temperature coefficient [V / ° C]), using constants such as solar radiation of 1.0 kW / m ² and temperature of 25 ° C in standard condition (STC) Evaluate with. Thereby, even if conditions, such as the amount of solar radiation at the time of measurement and temperature, differ, determination by comparison with a standard characteristic is enabled.

Here, each constant used for conversion to the reference state is a value determined in a normal state (standard state), and is not a value obtained in consideration of the loss in a state where a loss is actually generated. Therefore, when there is a loss due to failure, deterioration, etc. (which may be a measurement error) at a solar radiation amount and temperature different from the reference state, a 25 ° C. correction is made based on the formula of JIS-C8913, Even if 1.0 kW / m ² is given and converted to the reference state, the loss cannot be grasped as a correct value unless converted using values of R _s and K that take into account the loss that has actually occurred. May be wrong.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solar cell inspection system that can appropriately evaluate the occurrence of a loss based on the electrical characteristics of the solar cell string and inspects the presence or absence of a failure or deterioration of the solar cell system. And a solar cell inspection method.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.

  A solar cell inspection system according to a representative embodiment of the present invention is a solar cell inspection system that inspects for the presence or absence of abnormality of a solar cell string composed of one or a plurality of solar cell modules connected in series. A current-voltage characteristic measurement unit that measures a first current-voltage characteristic of the battery string; and an inspection unit that determines whether the solar cell string is abnormal based on the first current-voltage characteristic.

  The inspection unit calculates an operating temperature of the solar cell string based on the first current-voltage characteristic, and a second current-voltage in a normal state of the solar cell string based on the operating temperature. Calculating a reference gradient to be treated as a value related to the slope in the diode region of the characteristic; calculating a measurement gradient that is a value related to the slope in the diode region of the first current-voltage characteristic; The presence or absence of abnormality of the solar cell string is determined based on the comparison.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  That is, according to the representative embodiment of the present invention, based on the electrical characteristics of the solar cell string, it is possible to appropriately evaluate the loss when it occurs, such as failure or deterioration of the solar cell system. The presence or absence can be inspected.

It is the figure which showed the outline | summary about the example of the method of determining the presence or absence of a failure from the electric current-voltage characteristic of the solar cell string in Embodiment 1 of this invention. It is the flowchart which showed the outline | summary about the example of the method of determining abnormality of the solar cell string in Embodiment 1 of this invention. It is the flowchart which showed the outline | summary about the example of the solar radiation amount and temperature calculation process in Embodiment 1 of this invention. It is the figure which showed the outline | summary about the example which calculates the inclination between two points | pieces in the diode area | region in Embodiment 1 of this invention. It is the flowchart which showed the outline | summary about the example of the method of determining abnormality of the solar cell string in Embodiment 2 of this invention. It is the flowchart which showed the outline | summary about the example of the series resistance calculation process in Embodiment 2 of this invention. It is the figure which showed the outline | summary about the example in case the disconnection has arisen in the solar cell string in Embodiment 3 of this invention. It is the flowchart which showed the outline | summary about the example of the method of determining abnormality of the solar cell string in Embodiment 3 of this invention. It is the flowchart which showed the outline | summary about the example of the method of determining abnormality of the solar cell string in Embodiment 4 of this invention. It is the figure which showed the outline | summary about the example which calculates shunt resistance from the measurement characteristic in Embodiment 4 of this invention. It is the figure which showed the outline | summary about the structural example of the general photovoltaic power generation system. It is the figure which showed the outline | summary about the structural example of the general solar cell string. It is the figure which showed the outline | summary about the example of the mechanism which detects the failure of each solar cell string in a common solar power generation system. It is the figure which showed the outline | summary about the structural example of the general solar cell test | inspection system. (A)-(c) is the figure which showed the outline | summary about the example of the method of determining the presence or absence of a failure from the current-voltage characteristic of the solar cell string in a prior art. (A)-(c) is the figure which showed the outline | summary about the other example of the method of determining the presence or absence of a failure from the current-voltage characteristic of the solar cell string in a prior art.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  In the following, in order to make the features of the present invention easier to understand, the description will be made in comparison with the prior art.

<Overview>
FIG. 11 is a diagram showing an outline of a configuration example of a general photovoltaic power generation system. In the photovoltaic power generation system 1, one or more solar cell strings 11 in which a plurality of solar cell modules 110 are connected in series are connected in parallel via connection in the connection box 20, and are further aggregated to obtain DC / It has a configuration connected to the power system 33 via a DC converter 31 and an inverter 32, or a PCS (Power Conditioning System) (not shown) including these. Thereby, the electric power generated by each solar cell string 11 can be output to the electric power system 33. A plurality of solar cell strings 11 connected in parallel may be arranged side by side to form a solar cell array 10, and a connection box 20 may be provided for each solar cell array 10. In addition, in order to prevent the backflow of the electric current produced | generated by each solar cell string 11 in the connection box 20, the backflow prevention diode 21 is connected.

  FIG. 12 is a diagram showing an outline of a configuration example of a general solar cell string 11. The solar cell string 11 shown in the drawing on the right side has a configuration in which a plurality of solar cell modules 110 are connected in series as described above. Each solar cell module 110 has a configuration in which a plurality of solar cells 111 are connected in series as shown in the center diagram, and further, a bypass diode 112 for failure or the like is connected in parallel therewith. Each solar cell 111 is composed of a semiconductor element or the like that converts sunlight into electric power, and is represented by an equivalent circuit as shown in the left figure as a so-called PV (PhotoVoltaic) cell model.

  FIG. 13 is a diagram showing an outline of an example of a mechanism for detecting a failure of each solar cell string 11 in a general photovoltaic power generation system 1. In the example of FIG. 13, a current-voltage characteristic measuring instrument (curve tracer) 40 is connected to a terminal corresponding to the solar cell string 11 to be inspected in the connection box 20, and the current-voltage characteristic for each solar cell string 11. The structure which measures is shown. The current-voltage characteristic measuring instrument 40 has, for example, a configuration including an equivalent circuit including an electronic load, an ammeter, and a voltmeter as illustrated. As described above, the conventional technique employs a mechanism in which a current-voltage characteristic is obtained by measuring a current and a voltage for the solar cell string 11 to be inspected, and a failure is detected based on a deviation state from a normal state. . The other solar cell strings 11 are inspected by sequentially switching the connection destinations of the inspection terminals of the current-voltage characteristic measuring instrument 40.

  FIG. 14 is a diagram showing an outline of a configuration example of a general solar cell inspection system. The solar cell inspection system 2 includes a current-voltage characteristic measuring device 40 and an inspection device 43 including an information processing terminal such as a PC (Personal Computer). As the current-voltage characteristic measuring instrument 40, for example, a generally available portable device can be used, and an output current and a voltage are measured and a current-voltage characteristic (IV curve) is output. In order to acquire parameters such as the amount of solar radiation and temperature necessary for evaluating the deviation state between the measured current-voltage characteristics and the current-voltage characteristics under normal conditions, for example, the current-voltage characteristics measuring instrument 40 includes A temperature sensor such as a total 41 or a thermocouple 42 may be connected. The current-voltage characteristic measuring instrument 40 and the inspection device 43 may be configured as independent devices as in the example of FIG. 14, or may be configured as the same device or device.

  On the other hand, in the connection box 20 of the solar power generation system 1, a backflow prevention diode 21 and a DC (disconnector) 22 are installed in the wiring from each solar cell string 11. An MCCB (circuit breaker for wiring) 23 for the solar cell array 10 is also installed. In order to inspect the abnormality of the solar cell string 11, in the junction box 20, the DC 22 corresponding to the solar cell string 11 to be inspected is turned off, and for example, as shown in the drawing, current-voltage characteristics are applied to terminals and wiring portions. The measuring device 40 is connected. Information such as the current-voltage characteristics of the solar cell string 11, the amount of solar radiation, and the temperature measured and acquired by the current-voltage characteristic measuring instrument 40 is output to the inspection device 43. The presence / absence of an abnormality due to failure, deterioration, or the like is determined on the basis of the deviation from the normal state.

FIG. 15 is a diagram showing an outline of an example of a method for determining the presence / absence of a failure from the current-voltage characteristics of the solar cell string 11 in the related art. FIG. 15 shows an example of loss when the series resistance R _s is increased due to a failure or the like in the equivalent circuit of the solar battery cell 111 shown in the left diagram of FIG.

  Note that the mark (P100, P101, P110, P111, P101 ') on each current-voltage characteristic curve shown in FIG. 15 indicates the maximum power point. The power loss at the time of failure compared with the normal time can be obtained from the difference in power value at each maximum power point. In the following description, the power loss at the time of failure is expressed as “P100-P101”, for example.

In FIG. 15 (a), the dotted current-voltage characteristic curve shows the normal characteristic in a reference state with an amount of solar radiation of 1.0 kW / m ² and a temperature of 25 ° C. A solid line current-voltage characteristic curve indicates a characteristic at the time of failure when measured in a reference state. FIG. 15 (b) shows current-voltage characteristic curves under normal conditions and failures in a solar radiation amount of 0.5 kW / m ² and a temperature of 25 ° C., respectively.

FIG. 15 (c) shows a voltage-current characteristic curve measured at an amount of solar radiation of 0.5 kW / m ² and this in a standard state of an amount of solar radiation of 1.0 kW / m ² and a temperature of 25 ° C. according to the formula of JIS-C8913. The characteristic curve when converted into the value of 1 and the characteristic curve in the normal state in the reference state are respectively shown. The power loss (P100-P101 ′) converted to the reference state is smaller than the power loss at the time of failure (P100-P101) directly measured in the reference state of FIG. In this case, the actual loss may be underestimated and the failure may not be properly grasped.

Similarly, FIG. 16 is a diagram showing an outline of another example of a method for determining the presence / absence of a failure from the current-voltage characteristics of the solar cell string 11 in the conventional technology. FIG. 16 shows an example of loss when the shunt resistance R _sh is reduced due to a failure or the like in the equivalent circuit of the solar battery cell 111 shown in the left diagram of FIG.

  In addition, the mark (P200, P201, P210, P211, P201 ') on each current-voltage characteristic curve shown in FIG. 16 indicates the maximum power point. The power loss at the time of failure compared with the normal time can be obtained from the difference in power value at each maximum power point. In the following description, the power loss at the time of failure is expressed as “P200-P201”, for example.

In FIG. 16 (a), the dotted current-voltage characteristic curve indicates the normal characteristic in a reference state with an amount of solar radiation of 1.0 kW / m ² and a temperature of 25 ° C. A solid line current-voltage characteristic curve indicates a characteristic at the time of failure when measured in a reference state. FIG. 16B shows current-voltage characteristic curves at normal time and failure in a state where the solar radiation amount is 0.4 kW / m ² and the temperature is 25 ° C.

FIG. 16 (c), the voltage measured at insolation 0.4kW / ^{m 2} - current characteristic curve, which solar radiation amount 1.0 kW / ^{m 2} by the equation of JIS-C8913, with a reference state of a temperature 25 ° C. The characteristic curve when converted into the value of 1 and the characteristic curve in the normal state in the reference state are respectively shown. The power loss (P200-P201 ′) converted into the reference state is larger than the power loss at the time of failure (P200-P201) directly measured in the reference state of FIG. In this case, contrary to the case of FIG. 15, the actual loss is overestimated, and for example, a case where a failure such as a measurement error is not a failure may be determined.

As described above, these results are based on the JIS-C8913 formula, and parameters such as R _s and K used in the conversion use values determined in a normal standard state, and are affected by a failure or the like. This is because the value considering the actual loss due to is not used.

<Embodiment 1>
In order to solve the above-described problem, the solar cell inspection system according to Embodiment 1 of the present invention is based on the measured current-voltage characteristic curve, and is described as a region where the diode characteristics are effective (hereinafter referred to as “diode region”). In this case, it is possible to determine an abnormality such as a failure or deterioration of the solar cell string 11 by calculating a normal inclination in the case of the solar cell string 11 and comparing it with an actual inclination in the measured current-voltage characteristic curve. is there. Thus, without using parameters such as R _s and K in a standard state that does not consider actual loss, it is necessary to appropriately grasp and evaluate the loss based on comparison with current-voltage characteristics at normal time. Is possible.

FIG. 1 is a diagram schematically showing an example of a method for determining the presence or absence of a failure from the current-voltage characteristics of the solar cell string 11 according to Embodiment 1 of the present invention. In the current-voltage characteristic curve of FIG. 1, the solid line indicates the current-voltage characteristic curve of the solar cell string 11 actually measured by the current-voltage characteristic measuring device 40 with the configuration shown in FIG. May be described as “measurement characteristics”). Here, the output voltage is zero, that is, the output current when the output is short-circuited is the short-circuit current I _sc , and the output current is zero, that is, the output voltage when the output is open is the open-circuit voltage V _oc .

  In the present embodiment, the short-circuit current and the open-circuit voltage are acquired from the measurement characteristics, and based on these, the current-voltage characteristic curve at normal time indicated by the dotted curve in FIG. The slope in the diode region (which may be described as “normal characteristics” in some cases) (hereinafter sometimes referred to as “reference gradient”) is calculated. In the diode region, the characteristic curve is substantially linear and can be treated as having a certain slope. The abnormality of the solar cell string 11 is determined by comparing the reference gradient with the gradient in the diode region in the measurement characteristics (hereinafter sometimes referred to as “measurement gradient”). These processes are performed by the inspection apparatus 43 by a process such as a software program based on the measurement characteristic data acquired by the current-voltage characteristic measuring instrument 40, for example.

  FIG. 2 is a flowchart showing an outline of an example of a method for determining an abnormality of the solar cell string 11 in the present embodiment. First, the current-voltage characteristic measuring device 40 measures the current-voltage characteristic of the solar cell string 11 to be inspected to obtain the measurement characteristic (S01). This process may be performed manually by operating the current-voltage characteristic measuring instrument 40, or may be automatically performed by an instruction or control from a software program on the inspection apparatus 43. Thereafter, the current-voltage characteristic measuring instrument 40 or the inspection device 43 acquires the values of the short-circuit current and the open-circuit voltage from the measurement characteristic data (S02).

Thereafter, the inspection device 43 executes a solar radiation amount / temperature calculation process for calculating the solar radiation amount and the temperature in the solar cell string 11 from the values of the short-circuit current and the open-circuit voltage in the measurement characteristics (S03). FIG. 3 is a flowchart showing an outline of an example of the solar radiation amount / temperature calculation process. Here, first, the solar radiation amount p [kW / m ² ] is calculated based on the value of the short-circuit current obtained in step S02 of FIG. 2 (S11). The amount of solar radiation p is represented by the following equation, where I _sc1 [A] is the short-circuit current value in the measurement characteristics and I _sc0 [A] is the short-circuit current value in the reference state (STC).

Note that the value of I _sc0 is a constant obtained as the specification of the solar cell module 110 and can be held or set in advance in the inspection device 43.

Next, the test | inspection apparatus 43 correct | amends the value of the open circuit voltage in 25 degreeC based on the value of the solar radiation amount p obtained by step S11 (S12). _Assuming that the open-circuit voltage value in the reference state is V _oc0 [V] and the reverse saturation current in the solar battery cell 111 is I _s [A], the following equation is established. Thus, V _oc0 is _changed to V ′ _oc0 . It can be corrected.

N _cell is the total number of solar cells 111 included in the solar cell string 11, and n _f , k, and q are constants such as a junction constant, a Boltzmann constant, and a load amount, respectively. The value of V _oc0 is a constant that can be obtained as the specification of the solar cell module 110. These constants can also be held or set in the inspection apparatus 43 in advance. V ′ _oc0 obtained by the correction is newly handled as V _oc0 .

Next, based on the open circuit voltage value obtained in step S02 in FIG. 2 and the corrected open circuit voltage value at 25 ° C. obtained in step S12, the inspection device 43 performs the following operation. The operating temperature T [K] is calculated (S13). When the open circuit voltage value in the measurement characteristics is V _oc1 [V], the operating temperature T is expressed by the following equation.

  Β [V / K] is a temperature characteristic coefficient of the open circuit voltage in the reference state, and is a constant that can be obtained as a specification of the solar cell module 110 and can be held or set in advance in the inspection device 43. .

  Next, the inspection device 43 recalculates the solar radiation amount p obtained in step S11 based on the value of the operating temperature T obtained in step S13 (S14). The solar radiation amount p corrected by the operating temperature T is expressed by the following equation.

  Α [A / K] is a temperature characteristic coefficient of the short-circuit current in the reference state, and is a constant that can be obtained as the specification of the solar cell module 110 and can be held or set in advance in the inspection device 43. .

  Thereafter, the inspection device 43 determines whether or not the recalculated value of the solar radiation amount p has converged (S15), and if it has converged, the solar radiation amount / temperature calculation process is terminated. If not converged, the process returns to step S12 and the calculation process of the operating temperature T and the solar radiation amount p is repeated again. Determination of whether it has converged can be performed by, for example, whether or not the amount of change in the amount of solar radiation p before and after the recalculation in step S14 is less than a predetermined threshold. Alternatively, the calculation process of the operating temperature T and the solar radiation amount p may be performed depending on whether or not the calculation process is repeated a predetermined number of times (for example, three times). As shown in the configuration example of FIG. 14, when the solar radiation meter 41 and the thermocouple 42 are provided and the solar radiation amount p and / or the operating temperature T can be directly measured, the measured values are directly used. be able to.

Returning to FIG. 2, next, the inspection device 43 extracts two points from the data of the diode region in the measurement characteristics (S04). The extraction method is not particularly limited, and an appropriate method can be used. Thereafter, the inspection device 43 calculates a reference gradient m ₀ that is treated as a gradient in the diode region in a normal state and a measurement gradient m ₁ that is a gradient between the two points extracted in step S04 (S05, S06).

FIG. 4 is a diagram showing an outline of an example of calculating the slope between two points in the diode region. FIG. 4A shows a state in which two points (V ₁ [V], I ₁ [A]) and (V ₂ [V], I ₂ [A]) are extracted from the diode region of the current-voltage characteristic curve. Show. Here, when the short-circuit current is I _sc [A] and the series resistance in the solar battery cell 111 is R _s [Ω], it is known that the following expression is established at each point.

  Here, when the difference between the two equations of Equation 5 is taken, the following equation is obtained.

In a normal state (standard state), since it can be handled that R _s ≈0, Equation 6 is as follows.

Further, the reference gradient m ₀ and the measurement gradient m ₁ can be obtained by transforming Equation 7 as the following equation and setting the left side to m ₀ and the right side to m ₁ .

Here, in the characteristic curve of FIG. 4A, when the vertical axis is converted to LN (short-circuit current × irradiation amount−current), a characteristic curve as shown in FIG. 4B is obtained. The two points (V ₁ , I ₁ ) and (V ₂ , I ₂ ) in the diode region in FIG. 4A are respectively represented by (V ₁ , LN (I _sc1 × p−I ₁ ) in FIG. 4B. ), (V ₂ , LN (I _sc1 × p−I ₂ )), the distance between the two points is almost a straight line as shown in FIG. The measurement gradient m ₁ in FIG. 4 indicates the gradient (the reciprocal according to Equation 8).

This measurement gradient m ₁ is equal to the reference gradient m _{0 as} shown in Equation 8. In the equation of the reference gradient m ₀ , parameters other than the operating temperature T are constants obtained from specifications and the like, so the value of the reference gradient m ₀ is determined by the operating temperature T. Here, Equation 8 assumes a normal state (standard state), and when a loss occurs during an abnormality such as a failure, the reference gradient m ₀ is not changed, but is extracted from the measurement characteristics ( The value of the measurement gradient m ₁ calculated using the values of V ₁ , I ₁ ) and (V ₂ , I ₂ ) as parameters changes. Accordingly, since the value of the measurement gradient m ₁ is not equal to the reference gradient m ₀ and deviates, it is possible to determine an abnormality such as a failure by comparing m ₀ and m ₁ . In this sense, the reference gradient m ₀ can be handled as a reference value for determining and diagnosing abnormality.

Accordingly, the inspection device 43 determines whether or not the difference between m ₀ and m ₁ (value of m ₀ −m ₁ ) is larger than a predetermined threshold (S07). If the difference is larger, the solar cell string 11 is normal. It is determined that there is a certain value (S08), and if it is equal to or less than a predetermined threshold value, it is determined that there is an abnormality (S09), and the process is terminated. The predetermined threshold value can be appropriately set to a value of zero or more. Also, rather than the difference between the m ₀ and m _1, or may be determined based on the ratio.

As described above, according to the solar cell inspection system of Embodiment 1 of the present invention, two points (V ₁ , I ₁ ), (V ₂ , I ₂ ), and the values of the short-circuit current and the open-circuit voltage, the amount of solar radiation p, the operating temperature T obtained therefrom, and the various constants including only those obtained as the specifications of the solar cell module 110, the reference gradient m ₀ and measurement gradient m ₁ are respectively calculated and compared. Thereby, it is possible to determine the presence or absence of abnormality in the solar cell string 11 by appropriately evaluating the loss without using a parameter that needs to consider the influence of the loss.

<Embodiment 2>
In the method of the first embodiment described above, the presence or absence of abnormality in the solar cell string 11 can be determined by comparing the reference gradient m ₀ and the measurement gradient m ₁ . However, it is impossible to determine what cause the abnormality is based on, or which parameter value is detected because it is abnormal. Further, since the series resistance R _s can be regarded as 0 in a normal state, it is handled as such. In particular, the cause of the abnormality is caused by the series resistance R _s in the equivalent circuit of the solar cell 111 in FIG. In some cases, the accuracy of determination may be lowered by handling R _s ≈0.

Therefore, in order to solve the above-described problem, the solar cell inspection system according to the second embodiment of the present invention has a series resistance R _s when comparing the reference gradient m ₀ and the measurement gradient m ₁ in the _first embodiment. The value of the measurement gradient m ₁ is corrected by correcting the values of V ₁ and V ₂ at the two points in the diode region while incrementing the value by a constant amount. As a result, the value of R _s when the difference between m ₀ and m ₁ after correction (value of m ₀ −m ₁ ) is greater than a predetermined threshold is obtained, and based on this, the solar cell string 11 is normal whether, if abnormal makes it possible to determine whether the abnormality caused by the series resistance R _s.

  FIG. 5 is a flowchart showing an overview of an example of a method for determining an abnormality of the solar cell string 11 in the present embodiment. A series of processing from step S21 to S24 is the same as that from step S01 to S04 in the flowchart of the example of FIG.

If two points (V ₁ , I ₁ ) and (V ₂ , I ₂ ) in the diode region in the measurement characteristics are extracted in step S24, then the inspection device 43 performs a series resistance calculation process for calculating the series resistance R _s. Perform (S25). FIG. 6 is a flowchart outlining an example of the series resistance calculation process. Here, first, similarly to step S05 of FIG. 2 of the first embodiment, the reference gradient m ₀ is calculated based on the above equation (S31). Thereafter, the value of the series resistance R _s is initialized to zero (S32), and the voltages V ₁ and V ₂ at two points in the diode region are corrected by the following formulas based on the value of R _s (S33).

Thereafter, using the corrected values of V ₁ and V ₂ , the measurement gradient m ₁ is calculated based on the above equation (8), similarly to step S 06 in FIG. 2 (S 34).

Thereafter, similarly to step S07 in FIG. 2, it is determined whether or not the difference between m ₀ and m ₁ (value of m ₀ −m ₁ ) is larger than a predetermined threshold (S35). If it is less than or equal to the predetermined threshold value, the value of R _s is incremented by a fixed amount (0.001 [Ω] in the example of FIG. 6) (S36), and the process returns to step S33 to again correct the voltage and measure the gradient m. Repeat the calculation of ₁ . If the difference is larger than the predetermined threshold value in step S35, the value of R _s at this time is estimated as the value of series resistance R _s contributing to the loss, and the process is terminated.

Returning to FIG. 5, next, the inspection device 43 determines whether or not the value of the series resistance R _s calculated in step S25 is larger than a predetermined threshold (S26). If it is larger than the predetermined threshold, it is determined that the abnormality is caused by the series resistance R _s (S27), and the process is terminated. The predetermined threshold value can be appropriately set to a value greater than zero. If the value of R _s is equal to or smaller than the predetermined threshold value in step S26, it is determined that the state is normal (S28), and the process is terminated.

As described above, according to the solar cell inspection system according to the second embodiment of the present invention, when the reference gradient m ₀ and the measurement gradient m ₁ are compared, the value of the series resistance R _s is set to a certain amount. By correcting the values of V ₁ and V ₂ at two points in the diode region while incrementing by the value, and correcting the value of the measurement gradient m ₁ , the value of the series resistance R _{s is} compared with the reference gradient m _0. calculate. By evaluating the value of R _s , it is possible to determine whether the solar cell string 11 is normal or not, and if it is abnormal, whether it is abnormal due to the series resistance R _s and the degree of abnormality. Is possible.

<Embodiment 3>
In the above-described method according to the second embodiment, an abnormality caused by the series resistance R _s can be determined. As another cause of the abnormality, for example, a disconnection may occur in the solar cell string 11. . FIG. 7 is a diagram showing an outline of an example in which a disconnection occurs in the solar cell string 11. The upper diagram shows a part of a plurality of solar cell modules 110 connected in series in the solar cell string 11. Here, when a disconnection occurs due to a failure or the like in any part of the configuration in which a plurality of solar cells 111 in the solar cell module 110 are connected in series, the current in the solar cell module 110 is an arrow in the figure. As shown in FIG.

In this case, since there is no voltage corresponding to the power generation voltage of the solar cell module 110, the measurement characteristic is such that the normal characteristic is translated in the negative direction of the voltage as shown in the lower diagram of FIG. The measurement gradient and the reference gradient are almost the same. Therefore, as in the _first and second embodiments, it is difficult to detect the presence or absence of disconnection by comparing the measurement gradient m ₁ with the reference gradient m ₀ . On the other hand, at the time of disconnection, the operating temperature T obtained by the above equation 3 is calculated higher than the actual temperature.

Therefore, the solar cell inspection system according to Embodiment 3 of the present invention has the maximum power point (V _max ′, I _max ′) in the measurement characteristics shown in the lower diagram of FIG. 7 at the operating temperature T of I _max ′. By calculating the voltage value V _max1 and evaluating the amount of movement of the voltage of the measurement characteristic in the negative direction based on the ratio of this to V _max ′, it is possible to determine the presence or absence of disconnection.

  FIG. 8 is a flowchart showing an outline of an example of a method for determining an abnormality of the solar cell string 11 in the present embodiment. A series of processing from step S41 to S47 is the same as that from step S21 to S27 in the flowchart of the example of FIG.

When the value of R _s is equal to or smaller than the predetermined threshold value in step S46, in the present embodiment, the inspection apparatus 43 next extracts the maximum power point (V _max ′, I _max ′) from the measurement characteristic data. (S48) Further, the normal voltage value V _max1 at the operating temperature T of I _max ′ is calculated by the following equation (S49).

Here, as shown in FIG. 4A and the like, V ₂ is an actual measurement value in the vicinity of the open circuit voltage V _oc and is a voltage value lower than a normal value. In Formula 10, the voltage at I _max ′ is obtained with reference to V ₂ , V _max is not considering the series resistance, and V _max1 is considering. Since N _cell is multiplied on the basis of V ₂ , the calculated voltage at the time of disconnection is calculated to be lower than the actual voltage.

Thereafter, the inspection apparatus 43 determines whether or not the ratio (V _max1 / V _max ′) between V _max1 and V _max ′ is less than a predetermined threshold (S50). The predetermined threshold value can be appropriately set to a value greater than zero. Further, instead of the ratio between V _max1 and V _max ′, the determination may be based on a difference. When the ratio is less than the predetermined threshold in step S50, it is determined that the disconnection has occurred in the solar cell string 11 on the assumption that the moving amount of the voltage of the measurement characteristic in the negative direction is large (S51), and the process is terminated. . On the other hand, if it is equal to or greater than the predetermined threshold, it is determined that the state is normal (S52), and the process is terminated.

As described above, according to the solar cell inspection system according to Embodiment 3 of the present invention, when the value of series resistance R _s is not zero but is equal to or lower than a predetermined threshold value, the maximum power point (V _max For ', I _max '), calculate the voltage value V _max1 at the operating temperature T of I _max ', and evaluate the amount of movement of the voltage of the measurement characteristic in the negative direction based on the ratio of this to V _max ' Thus, it is possible to determine the presence or absence of disconnection.

<Embodiment 4>
In the methods of the _second and third embodiments described above, the abnormality caused by the series resistance R _s and the disconnection can be determined. As another cause of the abnormality, for example, in the equivalent circuit of the solar battery cell 111 in FIG. This may be caused by a decrease in the value of the shunt resistor R _sh . For example, the shunt resistance R _sh decreases due to deterioration of the pn junction portion in the solar battery cell 111, but may be grasped small due to a measurement error in the current-voltage characteristic. When the shunt resistance R _sh is reduced, as shown in the example of FIG. 16, a large loss occurs even in a low voltage region other than the diode region in the current-voltage characteristics.

Therefore, the solar cell inspection system according to the fourth embodiment of the present invention calculates the shunt resistance R _sh from the measurement characteristics, and determines whether there is an abnormality caused by the shunt resistance R _sh based on the value. Make it possible.

  FIG. 9 is a flowchart showing an outline of an example of a method for determining an abnormality of the solar cell string 11 in the present embodiment. The processing in steps S61 and S62 is the same as steps S01 and S02 in the flowchart of the example of FIG.

In the present embodiment, next, the inspection device 43 calculates the shunt resistance R _sh [Ω] from the measurement characteristic data (S63). FIG. 10 is a diagram showing an outline of an example in which the shunt resistance R _sh is calculated from the measurement characteristics. In order to calculate R _sh , two points (V ₃ [V], I ₃ [A]) and (V ₄ [V], I ₄ [A]) from the low voltage region other than the diode region are obtained from the measurement characteristic data. Are extracted, and R _sh corresponding to the slope between two points is calculated and estimated based on these values.

Returning to FIG. 9, next, the inspection apparatus 43 determines whether or not the value of the shunt resistance R _sh calculated in step S63 is less than a predetermined threshold (S64). The predetermined threshold value can be appropriately set to a value greater than zero. If it is less than the threshold, it is determined whether or not the number of times determined to be less than the threshold is the second time (S65). If it is the first time, there is a possibility of a measurement error in the current-voltage characteristic, so the process returns to step S61 again and the process is repeated from the measurement of the current-voltage characteristic. If it is the second time, it is determined that there is no measurement error, it is determined that the abnormality is caused by the shunt resistance R _sh (S66), and the process is terminated.

On the other hand, if the value of R _sh is greater than or equal to the threshold value in step S64, the process proceeds to step S67. The series of processing from step S67 to step S76 is performed in steps S43 to S43 in the flowchart of the example of FIG. Since it is the same as the series of processes up to step S52, the description thereof will be omitted.

As described above, according to the solar cell inspection system according to a fourth embodiment of the present invention, to calculate the shunt resistance R _sh from the measured characteristics, based on its value, the shunt resistor R _sh also include measurement error It is possible to determine whether or not there is an abnormality caused.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. . Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

  The present invention is applicable to a solar cell inspection system and a solar cell inspection method for detecting a failure of a solar cell module or a string.

1 ... Solar power generation system, 2 ... Solar cell inspection system,
10 ... solar cell array, 11 ... solar cell string,
20 ... Junction box, 21 ... Backflow prevention diode, 22 ... DC (disconnector), 23 ... MCCB (breaker for wiring),
31 ... DC / DC converter, 32 ... inverter, 33 ... power system,
40 ... Current-voltage characteristic measuring instrument, 41 ... Pyrometer, 42 ... Thermocouple, 43 ... Inspection device,
110 ... solar cell module, 111 ... solar cell, 112 ... bypass diode.

Claims (8)

A solar cell inspection system for inspecting the presence or absence of abnormality of a solar cell string composed of one or a plurality of solar cell modules connected in series,
A current-voltage characteristic measuring unit for measuring a first current-voltage characteristic of the solar cell string;
An inspection unit that determines the presence or absence of abnormality of the solar cell string based on the first current-voltage characteristic,
The inspection unit
Extracting a first short-circuit current and a first open-circuit voltage in the first current-voltage characteristic;
Calculating an operating temperature of the solar cell string based on the first open-circuit voltage and the second open-circuit voltage in a reference state;
Based on the first short-circuit current, the second short-circuit current in the reference state, and the operating temperature, calculate the solar radiation amount in the solar cell string,
Two points are extracted from the diode region of the first current-voltage characteristic, and for each point, the voltage value is taken as one axis, and the current value is subtracted from the value obtained by multiplying the short-circuit current and the amount of solar radiation. Calculating a measurement gradient that is a value related to the slope between the points when the logarithmized value is taken as the other axis,
Determining whether the solar cell string is abnormal based on a comparison between a reference gradient obtained by multiplying the operating temperature by a predetermined constant and the measured gradient;
Solar cell inspection system. The solar cell inspection system according to claim 1,
The inspection unit estimates a series resistance value in a solar battery cell in the solar battery module based on a comparison between the reference slope and the measurement slope, and based on the estimated series resistance value, the series resistance To determine whether there is an abnormality caused by
Solar cell inspection system. The solar cell inspection system according to claim 1,
The inspection unit extracts a value of a first current and a first voltage at a maximum power point in the first current-voltage characteristic, and corresponds to the first current at a normal time at the operating temperature. The second voltage of the first current-voltage characteristic is calculated based on the comparison between the second voltage and the first voltage, and the amount of movement of the voltage from the normal state in the negative direction is calculated based on the comparison between the second voltage and the first voltage. Evaluate and determine the presence or absence of abnormality due to disconnection in the solar cell module,
Solar cell inspection system. The solar cell inspection system according to claim 1,
The inspection unit estimates a shunt resistance value in a solar battery cell in the solar battery module based on a slope of the first current-voltage characteristic other than a diode region, and based on the shunt resistance value, Determining the presence or absence of an abnormality due to the shunt resistance;
Solar cell inspection system. A solar cell inspection method for inspecting the presence or absence of abnormality of a solar cell string composed of one or a plurality of solar cell modules connected in series,
Measuring a first current-voltage characteristic of the solar cell string;
Extracting a first short-circuit current and a first open-circuit voltage in the first current-voltage characteristic;
Calculating an operating temperature of the solar cell string based on the first open-circuit voltage and the second open-circuit voltage in a reference state;
Calculating the amount of solar radiation in the solar cell string based on the first short-circuit current, the second short-circuit current in a reference state, and the operating temperature;
Two points are extracted from the diode region of the first current-voltage characteristic, and for each point, the voltage value is taken as one axis, and the current value is subtracted from the value obtained by multiplying the short-circuit current and the amount of solar radiation. Calculating a measurement gradient that is a value related to the slope between the points when the logarithmically converted value is taken as the other axis;
Multiplying the operating temperature by a predetermined constant to calculate a reference gradient;
Determining whether the solar cell string is abnormal based on a comparison between the reference gradient and the measurement gradient,
Solar cell inspection method. In the solar cell inspection method according to claim 5 ,
Further, estimating a series resistance value in the solar cells in the solar cell module based on the comparison between the reference gradient and the measurement gradient;
Determining the presence or absence of abnormality due to the series resistance based on the estimated value of the series resistance,
Solar cell inspection method. In the solar cell inspection method according to claim 5 ,
Further, a value of the first current and the first voltage at the maximum power point in the first current-voltage characteristic is extracted, and a second value at normal time at the operating temperature corresponding to the first current is extracted. Calculating the voltage of
Based on the comparison between the second voltage and the first voltage, the amount of movement of the first current-voltage characteristic in the negative direction of the voltage from the normal state is evaluated. Determining whether there is an abnormality due to disconnection of
Solar cell inspection method. In the solar cell inspection method according to claim 5 ,
Furthermore, based on the slope of the first current-voltage characteristics other than the diode region, estimating a shunt resistance value in the solar battery cell in the solar battery module;
Determining whether there is an abnormality caused by the shunt resistance based on the value of the shunt resistance,
Solar cell inspection method.