JP2004287787A - Failure detection device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a failure of a solar battery not by relative comparison but with an absolute measurement value. <P>SOLUTION: It is determined whether or not the output of a solar battery string is connected to a load (S1-S2). When the output of the solar battery string is not connected to the load, voltage is applied to the solar battery string to measure the resistance value (S3-S9), and the failure of a group is determined based on the measured resistance value (S10-S12). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
FIELD OF THE INVENTION
The present invention relates to a failure detection device and a method thereof, and for example, relates to a device and a method for measuring a shunt resistance value of a solar cell and detecting a failure of the solar cell.
[0002]
[Prior art]
There are various methods for detecting solar cell failure. FIG. 1 shows a configuration of a general solar cell failure detection device 906.
[0003]
The output powers of the plurality of solar cell strings 902 are respectively guided to the connection box 907, and are connected in parallel after passing through the DC breaker 903, the surge absorber 904 and the backflow prevention diode 905 in the connection box 907. After that, the output power of the solar cell is supplied to the power conditioner 908.
[0004]
The current measuring device 909 of the failure detection device 906 measures the current flowing between each solar cell string 902 and the power conditioner 908, and inputs the measurement result to the control circuit 910. The control circuit 910 always integrates the current value of each solar cell string 903 to calculate an average current per unit time. Then, when the ratio of the average current value of each string to the average current value of the string having the maximum average current becomes equal to or less than the set value, control circuit 910 counts up the internal counter. Further, when the counted number exceeds a predetermined value, the control circuit 910 determines that the output is lower than expected and issues an alarm.
[0005]
A solar cell failure detection device having such a configuration is disclosed in, for example, JP-A-2000-214938.
[0006]
The above solar cell failure detection method has the following problems.
(1) Since the judgment is made by comparing the strings, it is possible to cope with a catastrophic failure in which only one solar cell string causes a decrease in output, but the output of the entire solar cell array is decreased. It cannot be used for such a failure or for estimating the life of a solar cell.
(2) For example, when some strings are shaded for ten and several days due to construction of a neighboring house, or when some strings are always shaded in winter due to a nearby large tree, there is no trouble. Nevertheless, in order to cope with the case where an alarm is issued, it is necessary to change the set value one by one.
[0007]
Note that a string or array in which a plurality of solar cells are serialized or parallelized may be referred to as an aggregate, but for convenience, a single solar cell alone is also referred to as an aggregate.
[0008]
[Patent Document]
JP 2000-214938 A
[Problems to be solved by the invention]
The present invention is intended to solve the above-mentioned problems individually or collectively, and has an object to detect a failure of a solar cell by an absolute measurement value, not a relative comparison.
[0010]
[Means for Solving the Problems]
The present invention has the following configuration as one means for achieving the above object.
[0011]
The present invention, when detecting a failure of an aggregate in which one or more solar cells are serialized or parallelized, determines whether the output of the aggregate and the load are connected, the aggregate When the output is not connected to the load, a voltage is applied to the aggregate to measure the resistance value of the aggregate, and a failure of the aggregate is determined based on the measured resistance value.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
[Overview]
FIG. 2 is a diagram showing the effect of a decrease in the shunt resistance value on the power generation amount. Based on the power generation amount data of samples having sufficiently high shunt resistance values (ie, normal samples) actually measured in various parts of Japan, FIG. 7 shows a result of simulating how the amount of generated power changes due to a change in resistance value. Of course, the accuracy of the simulation has been verified by comparing the result of the simulation with the amount of generated power of the sample in which a short circuit has actually occurred. As can be seen from the results shown in FIG. 2, the decrease in the shunt resistance starts to gradually affect the amount of generated power around 50 kΩ · cm 2 or less, and when the value falls below 10 kΩ · cm 2, the amount of generated power decreases rapidly. cause.
[0013]
In the present embodiment, the failure of the solar cell is detected by focusing on the decrease in the shunt resistance value of the solar cell. By detecting the decrease in the shunt resistance value of the solar cell, it is not necessary to perform the failure of the solar cell by the relative comparison as described above.
[0014]
Further, in the method of detecting the shunt resistance value of the solar cell, even if a part of the solar cell array is replaced, its influence can be completely ignored in determining a failure. As a result, the shunt resistance of an unreplaced solar cell decreases due to aging, etc., and can be regarded as a failure when it finally decreases until it affects power generation, thus maximizing the life of the solar cell. In addition to being usable, the remaining life can be estimated from the shunt resistance value of the solar cell, and the solar cell having a short life can be replaced in advance.
[0015]
Note that the failure detection method of the present embodiment is particularly effective in a thin-film solar cell having a relatively large number of short-circuit failure modes. The solar cell does not always fall into the short-circuit failure mode, but has various failure modes. Therefore, it is preferable that the failure determination of the solar cell be performed not only by one method but also by using some well-known failure detection methods.
[0016]
[Constitution]
Hereinafter, a solar cell failure detection device according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 3 is a block diagram illustrating a basic configuration example of the connection box 3 and the solar cell failure detection device 9 of the embodiment. Note that, like the connection box 907 shown in FIG. 1, the connection box 3 includes a DC breaker 903 and a surge absorber 904, but these are omitted in FIG.
[0018]
The output of the solar cell string 1, which is an aggregate of solar cells, is supplied to the connection box 3, and is supplied to the power conditioner 4 through the backflow prevention diode 2 in the connection box 3. Note that the failure detection device 9 shows an example of connecting a group of solar cells having a string configuration that is generally used frequently. However, a case where a group of solar cells connected in parallel is connected can also be used.
[0019]
In the failure detection device 9, a variable output type bipolar DC power supply device 5 is connected to the solar cell string 1 through a relay 6. The positive electrode of the DC power supply 5 is connected to the positive electrode of the solar cell string 1, and the negative electrode is connected to the negative electrode of the solar cell string 1.
[0020]
The output voltage of the solar cell string 1 is divided by the resistor voltage divider 7, input to the control circuit 10, and converted into digital information by the A / D converter in the control circuit 10.
[0021]
The current value supplied from the solar cell string 1 to the power conditioner 4 is converted into a voltage signal by the current measuring device 8 and input to the control circuit 10, and is converted into digital information by the A / D converter in the control circuit 10. You.
[0022]
FIG. 4 is a block diagram illustrating a configuration example of the control circuit 10.
[0023]
The CPU 104 controls the operation of the failure detection device 9 according to the program stored in the ROM area of the memory 105, using the RAM area of the memory 105 as a work memory. Then, when executing the test incorporated in the program, the CPU 104 causes the D / A converter 106 to output the control voltage Vc to be input to the DC power supply 5. DC power supply device 5 outputs an output voltage according to control voltage Vc.
[0024]
A voltage signal 101 indicating the current value of the string output from the current measuring device 8 and a voltage signal 102 indicating the output voltage value of the string output from the voltage divider 7 are converted into digital signals by the A / D converter 103, It is input to 104.
[0025]
The alarm device 11 and the relay 6 are connected to the I / O port 108 connected to the CPU 104, and the CPU 104 can sound the alarm device 11 and open and close the relay 6.
[0026]
As will be described later in detail, a prescribed resistance threshold is stored in the ROM area of the memory 105. Further, power for driving the control circuit 10 and the DC power supply 5 is obtained from a commercial power supply or from a secondary battery charged by the output of the solar cell string and the output of the solar cell string installed in the connection box 3. Just get it.
[0027]
[First Embodiment]
FIG. 5 is a block diagram illustrating a configuration example of the junction box and the failure detection device according to the first embodiment.
[0028]
The control circuit 10 keeps the relay 6 off while the solar cell string 1 is generating power.
[0029]
During the failure detection operation, it is necessary that the solar cell string 1 to be measured is not connected to a load such as the power conditioner 4. It is desirable to measure the shunt resistance value when the solar cell is not irradiated with sufficient light. In other words, it is preferable to measure the shunt resistance value when power is not being generated. Note that the shunt resistance during non-power generation does not necessarily mean the dark shunt resistance when a solar cell is placed in a dark room. Also includes the shunt resistance value in the state. The shunt resistance has a characteristic that is hardly affected by the external environment. However, when the solar radiation is very strong, the measurement result of the shunt resistance is affected by the fluctuation of the solar radiation. Therefore, in this embodiment, in order to eliminate such an influence, the shunt resistance value during non-power generation is measured.
[0030]
FIG. 6 is a flowchart showing a failure detection operation performed by the control circuit 10.
[0031]
The control circuit 10 measures the current flowing from each of the strings 1 to the power conditioner 4 in order to determine that the power is not being generated (S1). The power conditioner 4 cuts off the connection between the solar cell and the output side of the power conditioner 4 (for example, a commercial power system) when it determines that the power generation amount of the solar cell is small or the power generation state is not generated. Therefore, if the current flowing from each string 1 to the power conditioner 4 is zero or extremely small, it can be determined that the power is not generated (S2). The control circuit 10 detects the non-power generation state by performing steps S1 and S2 periodically, and executes the subsequent failure detection operation.
[0032]
When detecting the non-power generation state, the control circuit 10 causes the DC power supply device 5 to output a voltage V1 of about 1/3 to 1/2 of the open voltage of the solar cell string 1 (S3), and the test target solar cell The relay 6 connected to the string 1 is closed (S4), and the terminal voltage and current of the test target solar cell string 1 are measured (S5).
[0033]
Next, the control circuit 10 supplies the DC power supply device 5 with a voltage obtained by multiplying the forward drop voltage Vf of the bypass diode in the solar cell string 1 by the number of series of bypass diodes, for example, Vf = 0.8 V and the number of series is reduced. If it is 10, a negative voltage V2 within 8 V (for example, -8 V to 0 V) is output (S6). The negative voltage is a voltage having a polarity opposite to the direction of the voltage generated when the solar cell string 1 generates power. Then, the terminal voltage and current of the solar cell string 1 to be tested are measured (S7), and then the relay 6 is opened (S8).
[0034]
Next, the control circuit 10 calculates the shunt resistance value Rsh from the measured voltage change ΔV and the current change ΔI when the voltage applied to the test target solar cell string 1 is changed from V1 to V2 (S9). .
Rsh = ΔV / ΔI (1)
[0035]
Then, the control circuit 10 compares the calculated shunt resistance value Rsh with a specified resistance threshold value Th stored in the memory 105 (S10), and if Rsh <Th, the string to be tested fails (S111). , Rsh ≧ Th, it is determined to be normal (S12).
[0036]
The control circuit 10 repeats the processes of steps S3 to S11 for the number of the solar cell strings 1 and determines whether each solar cell string 1 is faulty or normal. Then, when it is determined that all the tests of the solar cell string have been completed (S13), the processing is terminated. The generation of the alarm when the failed solar cell string matches may be performed immediately after the determination in step S11 or after the above processing is completed.
[0037]
The DC power supply 5 may be an inexpensive switching power supply or a circuit in which a regulator is attached to a secondary battery charged from a solar cell as long as it can output the voltages V1 and V2 at the above two points. I do not care. The method of notifying the failure is not limited to the sounding of the alarm. For example, the LED corresponding to each solar cell string 1 blinks or the green LED is turned on for the normal solar cell string, and the failed solar cell For example, a red LED may be turned on for the string.
[0038]
Although the decrease in the shunt resistance value is expressed as a failure of the solar cell string 1, it is not a dangerous failure per se, but indicates the life of the solar cell. Therefore, even if there is a solar cell string 1 having a lowered shunt resistance, there is no problem even if the operation of the solar power generation device is continued. In view of this, an LED display or the like is used rather than sounding an alarm such as a buzzer. It is desirable to use quiet alarm means.
[0039]
The frequency of measurement once a day is sufficient. Further, a mechanical relay may be used as the relay 6, but reliability can be improved by using a semiconductor component such as a photo MOS relay.
[0040]
If the output voltage of the DC power supply 5 can be controlled accurately, the voltage divider 7 and the A / D converter for measuring the voltage ΔV can be omitted.
[0041]
The test may be performed in the daytime as long as the solar cell string 1 is disconnected from the load. However, in consideration of avoiding disturbance due to a sudden change in sunlight during the day, a certain time range (for example, at night) is set by a timer. It is desirable to perform stable measurement by using test conditions, measuring the voltage of the solar cell string 1 at 0 V as a measurement condition, or combining them. Obviously, if the night is added to the test conditions, it is obvious that the power conditioner 4 is stopped, so that steps S1 and S2 can be omitted.
[0042]
If it is possible to accurately measure that the open-circuit voltage of the solar cell string 1 is 0 V, it is not unfortunate to assume that the current value when V2 is 0 V is 0 A. In this case, although the accuracy is reduced because the measurement voltage range is narrow, the shunt resistance value Rsh (= V1 / I1) can be calculated from the voltage value and the current value when V1 is applied.
[0043]
[Second embodiment]
Hereinafter, a failure detection device according to a second embodiment of the present invention will be described. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0044]
FIG. 7 is a block diagram illustrating a configuration example of the failure detection device according to the second embodiment. The difference from the first embodiment is that the failure detection device 9 is built in the power conditioner 4 instead of in the junction box 3. The operation during the test is the same as in the first embodiment. However, the DC power supply 5 is not limited to an independent power supply and may be a circuit that rectifies and supplies power from a commercial power system as long as it can output the voltages V1 and V2 at the two points.
[0045]
The current measuring device 8 is arranged on a line connected to the power conversion circuit 41 because it is necessary to check the non-power generation state. If it is desired to accurately measure the current during the test, it may be arranged on each test line between the junction box 3 and the voltage divider 7.
[0046]
[Third embodiment]
Hereinafter, a failure detection device according to a third embodiment of the present invention will be described. In the third embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0047]
As long as the voltage V1 applied to the solar cell string 1 is accurately controlled, it is not necessary to measure the terminal voltage of the solar cell string 1 to be tested. Then, the maximum value Ith = V1 / Th of the current at the time of the test can be calculated from the resistance threshold value Th indicating the lower limit of the shunt resistance value Rsh. Therefore, if the current value I during the test does not exceed the maximum value Ith, it can be determined that the shunt resistance value Rsh is higher than the specified value.
[0048]
FIG. 8 is a block diagram illustrating a configuration example of a circuit that determines a failure based on a current value during a test.
[0049]
The voltage V (in) representing the current value sent from the current measuring device 8 is supplied to the hysteresis comparator 51, and is compared with the voltage Vref corresponding to the maximum value Ith of the current during the test. If V (in)> Vref, a signal is output from the comparator 51, latched by the latch 52 at the subsequent stage, and the LED 53 connected to the output terminal of the latch 52 is turned on to notify the failure of the corresponding solar cell string 1. I do.
[0050]
In this example, since it is assumed that the current value at the time of V2 = 0V is 0 A, the test is performed as accurately as possible, for example, when the open-circuit voltage of the solar cell string 1 is 0V. It is preferable to be able to do so.
[0051]
If a determination circuit as shown in FIG. 8 is used, the control circuit 10 does not necessarily need to use a CPU or the like, and the circuit can be simplified and the cost can be reduced.
[0052]
According to the embodiment described above, the following effects can be obtained.
(1) With a simple configuration, failure detection and life estimation of the entire solar cell can be performed.
(2) Accurate failure detection is possible.
(3) Failure detection and life estimation can be performed without being affected by the bypass diode.
(4) Quantitative failure detection and life estimation are possible.
[0053]
【The invention's effect】
As described above, according to the present invention, a failure of a solar cell can be detected not by a relative comparison but by an absolute measurement value.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a general solar cell failure detection device;
FIG. 2 is a diagram showing an influence on a generated power amount due to a decrease in a shunt resistance value;
FIG. 3 is a block diagram showing a basic configuration example of a connection box and a failure detection device.
FIG. 4 is a block diagram illustrating a configuration example of a control circuit;
FIG. 5 is a block diagram illustrating a configuration example of a connection box and a failure detection device according to the first embodiment;
FIG. 6 is a flowchart showing a failure detection operation performed by the control circuit;
FIG. 7 is a block diagram illustrating a configuration example of a failure detection device according to a second embodiment;
FIG. 8 is a block diagram illustrating a configuration example of a circuit that determines a failure based on a current value during a test.

Claims (11)

A detection method for detecting a failure of an aggregate in which one or more solar cells are serialized or parallelized,
Determine whether the output of the aggregate and the load are connected,
When the output of the aggregate and the load are not connected, measure the resistance value of the aggregate by applying a voltage to the aggregate,
A failure detection method comprising: determining a failure of the assembly based on the measured resistance value. The method according to claim 1, wherein the resistance value is calculated from a terminal voltage of the assembly when the voltage is applied and a measured value of a current flowing through the assembly. 2. The method according to claim 1, wherein voltages having different voltage values are sequentially applied to the assembly, a current value flowing through the assembly at each voltage application is measured, and the resistance value is calculated from a slope of a current with respect to the voltage. The described failure detection method. 4. The failure detection method according to claim 3, wherein a voltage applied to the aggregate is equal to or less than 1/2 of an open-circuit voltage of the aggregate. 4. The method according to claim 3, wherein when applying a negative voltage to the assembly, a voltage having an absolute value smaller than a product of a forward voltage of a bypass diode incorporated in the assembly and the number of series of the bypass diodes is applied. Alternatively, the failure detection method according to claim 4. The failure detection method according to claim 1, further comprising repeating the connection determination, the measurement, and the failure determination for the number of the assemblies. The failure detection method according to claim 1, wherein when the resistance value is equal to or smaller than a value obtained by dividing 50 kΩ by a total area of the solar cells constituting the assembly, the assembly is determined to be a failure. . 8. The failure detection method according to claim 1, wherein a current output from the assembly to a load is measured, and the connection is determined to be non-connected when the load current is exhausted. . The failure detection method according to any one of claims 1 to 7, wherein the connection is determined when the current time is nighttime. The failure detection according to any one of claims 1 to 7, wherein a generated voltage of the assembly is measured, and the non-connection is determined by comparing the generated voltage with a predetermined voltage threshold. Method. A power supply for supplying power to an aggregate of one or more solar cells serialized or parallelized;
Measuring means for measuring a current flowing between the power supply and the assembly,
Controlling the power supply, and control means for acquiring a measurement result of the measurement means,
The control unit controls the power supply to apply a voltage to the aggregate when the output of the aggregate and the load are determined to be disconnected based on the measurement result of the measurement unit, A failure detection device that determines a failure of the assembly based on a result.

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