JP6958146B2 - Arc detector - Google Patents

Description

According to the present invention, it is possible to specify the location where an arc is generated in each part of each string of the solar cell module and a power conditioning subsystem (hereinafter, abbreviated as PCS) that converts direct current from the solar cell module into alternating current. It relates to an arc detection device that can be used.

In the photovoltaic power generation system, which is becoming more widespread, the DC circuit is from the solar cell module to the PCS. In this DC circuit, the voltage is increased in order to improve the efficiency.
As the voltage increases, an arc may occur inside the solar cell module, in the connector part, the junction box, the output cable, etc. due to deterioration of parts, vibration, impact, damage due to an earthquake, or the like. The generation of the arc may cause various problems due to the high temperature of the arc.

As a conventional device for detecting arc generation, the one described in Patent Document 1 is known. When the arc detection protection device described in Patent Document 1 receives a detection signal from the detector, it executes the first step of opening the switch, and the execution of the first step causes the detection signal from the detector. When stopped, the second step of maintaining the open pole of the switch and notifying the power conditioner that an arc has occurred in the switch is executed, and even if the first step is executed, the sensor is used. When the detection signal continues, the third step of notifying the power conditioner that an abnormality has occurred in a portion higher than the switch is executed. In Patent Document 1, it is described that the detector is an optical sensor that is sensitive to the generation of an arc during power generation or an antenna that is sensitive to an electromagnetic wave signal generated during the generation of an arc by detecting light. ..

Japanese Unexamined Patent Publication No. 2014-42364.

However, in the arc detection protection device described in Patent Document 1, although the location where the arc is generated can be specified, the switch installed for each string is sequentially opened, and the presence / absence of the signal is repeated to generate the generation location. Is to identify. Therefore, a switch is required for each string, and in order to specify the arc generation location, the switch is opened, so that the opened string stops power generation. Further, since a switch is required, the technique of the arc detection protection device described in Patent Document 1 cannot be applied when only the arc generation is detected.

In the photovoltaic power generation system, the output cable of each string of the solar cell module is connected to the junction box, the wiring is integrated and connected to the PCS (centralized PCS-PV system), and the output cable of each string is individually connected. There is a configuration (multi-string PCS-PV system) that is directly connected to the PCS.
In such various configurations, the arc is made between the solar cell modules of each string, between each string and the junction box, or between each string and the directly connected PCS, between the junction box and the PCS, and so on. May occur. Therefore, it is important to be able to identify the location of the arc generation even in various configurations.

Therefore, an object of the present invention is to provide an arc detection device capable of identifying an arc generation location without stopping power generation by a solar cell module even in a photovoltaic power generation system having various configurations.

The arc detection device of the present invention arcs by comparing a measuring means for measuring the noise level of each output cable of each string of the solar cell module with a noise level from the measuring means and a first threshold value indicating arc generation. A second determination means for determining the occurrence and a second for identifying the relationship between the maximum value of the noise level of each string and the noise level of the other strings when the first determination means detects the occurrence of an arc. It is characterized by having a second determination means for determining whether an arc is generated in a string having a maximum noise level based on a threshold value or an arc is generated in a place other than each string. And.

According to the arc detection device of the present invention, first, the first determination means determines whether or not an arc has been generated by comparing the noise level from the measuring means with the first threshold value indicating the arc generation. If an arc is generated, it is determined by the second determination means based on a second threshold value for discriminating the relationship between the maximum value of the noise level and the noise level of another string. According to the second threshold value, when the difference between the maximum value of the noise level and the noise level of the other strings is small, it can be determined that the arc is generated at a place other than each string. Further, when the difference between the maximum value of the noise level and the noise level of another string is large, it can be determined that the arc is generated in the string having the maximum noise level.

The second determination means sets a predetermined ratio from the maximum value of the noise level of each string as the second threshold value, compares it with the noise level of each string, and the number of strings exceeding the second threshold value is 1. For example, it is determined that the arc is generated in the string having the maximum noise level, and if the number of strings exceeding the second threshold value is plural, the arc is generated in a place other than each string. It can be determined that there is.
The second determination means compares the noise level of each string with the noise level of each string by setting a predetermined ratio from the maximum value of the noise level of each string as the second threshold value.
As a result, if the number of strings exceeding the second threshold value is 1, it means that the noise level of the string having the maximum value is higher than the noise level of the other strings. It can be determined that an arc has been generated.
Further, when the number of strings exceeding the second threshold value is multiple, the difference between the noise level of the string having the maximum value and the noise level of other strings is small, and the noise wraps around each string from other than each string. Therefore, it can be determined that the arc is generated at a place other than each string.

The second determination means sets a threshold for determining the degree of the level difference between the maximum value of the noise level of each string and the second as the second threshold, and if the level difference is equal to or greater than the second threshold. , It can be determined that the arc is generated in the string having the maximum noise level, and if it is less than the second threshold value, it can be determined that the arc is generated in a place other than each string. ..
The second determination means compares the level difference between the maximum value of the noise level of each string and the second value with the second threshold value.
As a result, if the level difference is equal to or higher than the second threshold value, it means that the noise level of the string having the maximum value is larger than the noise level of the other strings. It can be determined that it has occurred.
If the level difference is less than the second threshold value, the difference between the noise level of the string having the maximum value and the noise level of the other strings is small, and it can be estimated that the noise wraps around each string from other than each string. Therefore, it can be determined that the arc is generated at a place other than each string.

The first determination means determines that an arc has been generated when the arc detection by comparing the noise level from the measuring means with the first threshold value indicating the arc generation reaches the number of times based on the third threshold value in succession. can.
When the number of noise levels that continuously exceed the first threshold value exceeds the third threshold value, the first determination means determines that an arc has occurred, and the accidentally generated noise is erroneously regarded as an arc noise due to the arc generation. It is possible to prevent detection.

A current measuring device that measures the circuit current from the solar cell module, the circuit current is compared with the fourth threshold value, the third threshold value is increased when the circuit current is small, and the circuit current is large when the circuit current is large. It may be provided with a threshold value setting means for reducing the third threshold value.
By the threshold value setting means, the circuit current measured by the current measuring device can increase or decrease the set value of the number of consecutive times indicated by the third threshold value used by the first determination means for determining the arc generation based on the fourth threshold value. ..

The level difference between the noise level from the measuring means and the first threshold value is compared with the fifth threshold value, the third threshold value is decreased when the level difference is small, and the third threshold value is large when the level difference is large. It may be provided with a threshold value setting means for increasing the threshold value.
The threshold value setting means can increase or decrease the set value of the number of consecutive times indicated by the third threshold value used by the first determination means to determine the arc generation based on the level difference between the noise level from the measuring means and the first threshold value. can.

When the noise level from the measuring means excluding the noise level exceeding the first threshold value is accumulated and the average value is calculated, and the level difference between the average value and the first threshold value deviates from the sixth threshold value. In addition, a threshold value setting means for increasing or decreasing the first threshold value so that the level difference becomes the sixth threshold value can be provided.
When the level difference between the average value of the noise levels and the first threshold value deviates from the sixth threshold value, the threshold value setting means increases or decreases the first threshold value so that the level difference becomes the sixth threshold value. Threshold can be obtained.

According to the arc detection device of the present invention, the measuring means measures the noise level of each output cable of each string to generate an arc in the string having the maximum noise level, or a string other than the above strings. Since it is possible to determine whether an arc has occurred at another location, it is possible to identify the arc generation location without stopping the power generation by the solar cell module in order to detect the arc generation location even in a photovoltaic power generation system with various configurations. Can be done.

It is a figure for demonstrating the structure of the solar power generation system which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the structure of the arc detection device of the solar power generation system shown in FIG. It is a flowchart for demonstrating the operation of the arc detection apparatus shown in FIG. It is a table for demonstrating the relationship between the arc noise generated in the trunk line and the arc noise generated in each string. It is a figure for demonstrating the structure of the 1st modification of the arc detection apparatus which concerns on Embodiment 1. It is a flowchart for demonstrating the operation of the 1st modification of the arc detection apparatus shown in FIG. It is a figure for demonstrating the structure of the 2nd modification of the arc detection apparatus which concerns on Embodiment 1. It is a figure for demonstrating the structure of the 3rd modification of the arc detection apparatus which concerns on Embodiment 1. It is a figure for demonstrating the structure of the 4th modification of the arc detection apparatus which concerns on Embodiment 1. It is a figure for demonstrating the operation of the 4th modification of the arc detection apparatus shown in FIG. 9, and is the figure for demonstrating the case where the level difference between a noise level and a 1st threshold value is large. It is a figure for demonstrating the operation of the 4th modification of the arc detection apparatus shown in FIG. 9, and is the figure for demonstrating the case where the level difference between a noise level and a 1st threshold value is small. It is a figure for demonstrating the structure of the arc detection apparatus which concerns on Embodiment 2 of this invention. It is a figure for demonstrating the operation of the arc detection apparatus shown in FIG.

[Embodiment 1]
The photovoltaic power generation system using the arc detection device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.
In the photovoltaic power generation system 10 shown in FIG. 1, an arc detection device 40 for identifying an arc generation location is installed in a centralized PCS-PV system.
The centralized PCS-PV system is integrated by the strings S (S1 to S4) to which the solar cell modules M are connected in series, the junction box 20 to which the output cables C1 to C4 from the strings S are connected, and the junction box 20. It is provided with a PCS 30 to which the connected wiring is connected.

The strings S (S1 to S4) are output by increasing the DC voltage output by the solar cell module M from 300 V to about 1500 V by connecting the solar cell modules M in series.

In the junction box 20, the positive electrode side of the output cables C1 to C4 from the strings S (S1 to S4) is connected, and the negative electrode side is connected via a rectifying element to form a trunk line and is connected to the PCS 30.
The PCS 30 supplies the output from the strings S (S1 to S4) as adjusted power to a load (not shown). The functions of the PCS30 include converting the direct current output from the strings S (S1 to S4) to alternating current, as well as maximum output operating point control (MPPT: Maxi).
mum Power Point Tracking) outputs the maximum power of the ever-changing environmental changes to the load.

As shown in FIG. 2, the arc detection device 40 includes a measuring means 410, a first determination means 420, a second determination means 430, a display means 440, and a contact output means 450.
The measuring means 410 has a function of measuring the noise level of each output cable C1 to C4 of each string S of the solar cell module M. The measuring means 410 includes a detector 411 (411a to 411d), a switching means 412, an A / D conversion means 413, and a frequency analysis means 414.

The detectors 411 (411a to 411d) are clamped and arranged for each output cable C1 to C4 from each string S.
The detector 411 can be a CT that outputs a current change superimposed on the direct current flowing from the solar cell module M to the output cables C1 to C4 to output a current corresponding to the magnetic change.

The switching means 412, A / D conversion means 413, frequency analysis means 414, first determination means 420, second determination means 430, display means 440, and contact output means 450 of the measurement means 410 are the device main body 400. It is stored in.
The frequency analysis means 414, the first determination means 420, and the second determination means 430 can be assumed to have an arc detection program executed by a microcomputer.

The switching means 412 shown in FIG. 2 can be a selector that sequentially selects the detectors 411a to 411d for each unit time and outputs the signal input from the detectors 411a to 411d.
The A / D conversion means 413 converts the analog signals from the detectors 411a to 411d into digital signals.

The frequency analysis means 414 captures a digital signal indicating the voltage converted by the A / D conversion means 413 for a certain period of time, and analyzes the frequency component as a continuous waveform. The frequency analysis means 414 uses an FFT (Fast Fourier Transform) to analyze the spectrum in a band of several hundred Hz to 100 kHz.

The first determination means 420 has a function of determining the arc generation in any string S by comparing it with the arc detection threshold value (first threshold value) set as an absolute value, based on the noise level from the measurement means 410. It has.

The second determination means 430 includes a second threshold value set as a relative value corresponding to the maximum value of the noise level of each string S1 to S4 when the first determination means 420 detects an arc generation, and each string S1 to S1. Comparing with the noise level S of S4, if the number of strings exceeding the second threshold value is 1, it is determined that an arc has occurred in the corresponding string S, and the number of strings exceeding the second threshold value may be plural. For example, it is determined that an arc is generated at a location other than the strings S1 to S4.

The display means 440 displays the arc generation location from the second determination means 430. The display means 440 can be an LCD, an LED lamp, or the like. In the first embodiment, as shown in FIG. 1, the display means 440 is an LED lamp, and the LED lamp is blinked corresponding to the strings S1 to S4 that exceed the second threshold value.
The contact output means 450 notifies the arc generation by opening or short-circuiting the contacts corresponding to the arc generation locations from the second determination means 430. The contact output means 450 can be, for example, a relay.

The operation of the arc detection device according to the first embodiment of the present invention configured as described above will be described with reference to FIGS. 1 to 4.
As shown in FIG. 3, the noise level of the arc noise of each string is measured (step S10). In this measurement, first, signals are sequentially input from the detectors 411a to 411d arranged in the output cables C1 to C4 shown in FIG. 1 by the switching means 412 shown in FIG. For example, the switching means 412 selects a signal from the detectors 411a to 411d every 10 ms and outputs the signal to the A / D conversion means 413.

The signal input to the A / D conversion means 413 is converted from an analog signal to a digital signal. Then, the frequency analysis means 414 analyzes the frequency component as a continuous waveform to measure the noise level of each output cable C1 to C4 of each string S shown in FIG.

Next, the first determination means 420 shown in FIG. 2 compares the noise level with the first threshold value (step S20).
Since the PCS 30 is a device for converting the direct current generated by the solar cell module M into an alternating current, switching noise (PCS noise) is constantly generated in the direct current circuit (string side circuit). The PCS noise contains a large amount of frequency components in the vicinity of several kHz to 100 kHz, and the noise level changes because the PCS 30 operates so as to perform maximum power conversion according to the power generation status of the solar cell module M.
The arc noise is a frequency band that overlaps with the PCS noise, but is generated at a higher level than the PCS noise. Therefore, the first threshold value is set to a value higher than the PCS noise and lower than the arc noise level.

Next, the first determination means 420 determines whether or not the noise level exceeds the first threshold value (step S30). If the noise level is equal to or lower than the first threshold value, the process proceeds to step S10. When the noise level is larger than the first threshold value, the determination is performed by the second determination means 430.

The second determination means 430 searches for the maximum value of the noise level (step S40). Next, the second determination means 430 calculates a predetermined ratio from the maximum value and sets it as the second threshold value (step S50).

Here, a predetermined ratio for determining a second threshold value for discriminating the relationship between the maximum value of the noise level of each string and the noise level of the other strings will be described in detail.
(When an arc occurs in the string)
First, when an arc is generated in any of the strings S1 to S4, most of the arc noise flows to the PCS30 and the string S in which the arc is generated, but in reality, a part of the arc noise is not generated in the string S. Also wraps around.
The wraparound ratio differs depending on the type of solar cell module M and the system circuit configuration, but can be expressed as the ratio when the "noise level of the ungenerated string" is divided by the "string noise level of the arc generated", for example, the ratio. Let it be A (%).

(When an arc occurs on the main line)
When an arc is generated on the trunk line (hereinafter referred to as a trunk line arc), the arc noise levels of the strings S1 to S4 are the same because the configurations of the solar cell modules M constituting each string S are the same. The generated power and impedance of S are also almost the same.
Therefore, since the arc noise passes through the PCS and flows evenly around all the strings, the noise level due to the arc of each string S is theoretically a value obtained by dividing the noise level of the trunk arc by the number of strings.
However, in reality, there are variations in the wraparound of arc noise to each string. The ratio of variation varies depending on the circuit configuration, the characteristics of the solar cell module M, and the like, but can be expressed as the ratio of the minimum value to the maximum value, and is defined as the ratio B (%).

(Determining the second threshold)
Considering the above two ratios A and B, the second threshold value needs to be specified at a ratio larger than the ratio A of the maximum noise level and smaller than the ratio B.
For example, if the ratio A is 10% and the ratio B is 70%, 40% is appropriate on average, so that the second threshold value can be the maximum value of the noise level × 0.4.
In this way, a second threshold value for discriminating the relationship between the maximum value of the noise level of each string and the noise level of the other strings can be determined.

(Arc detection)
As shown in FIGS. 4A and 4B, in the case of a trunk line arc, assuming that the noise level of the trunk line arc is 100, the strings S1 to S4 wrap around all the strings and flow around the trunk line. It is expected that noise levels of 24-26 will occur.
Further, when an arc is generated in the string S1 (hereinafter referred to as a string arc), assuming that the noise level of the string arc in the string S1 is 100, the trunk line and the strings S2 to S4 wrap around from the string S1. It is assumed that the noise level on the main line is 70 and the other strings S2 to S4 are 10 due to the flow.

In the table shown in FIG. 4A, since the first threshold value is 20, in the case of the trunk arc, all of the strings S1 to S4 are larger than the first threshold value, so that the determination proceeds to the determination based on the second threshold value. ..
Further, as shown in FIGS. 4A and 4C, in the case of the string arc, since the string S1 is larger than the first threshold value, the determination proceeds based on the second threshold value.

In the determination based on the second threshold value, in the case of the trunk arc shown in FIG. 4B, the maximum value of the noise level is 26, in which the noise level of the string S1 is larger than that of the other strings S2 to S4. Therefore, the second threshold value with the predetermined ratio of the maximum value as 40% is 26 × 0.4 = 10.
Therefore, in step S60, when the second determination means 430 compares the second threshold value with the noise levels of the strings S1 to S4, the noise level of the strings S1 is larger than the second threshold value, but the noise levels of the strings S2 to S4 are higher. It is determined that each noise level is also larger than the second threshold value.

In step S70, when the second determination means 430 determines that the number of strings having a noise level larger than the second threshold value is a plurality, the noise level of the string S1 that has become the maximum value and the noise level of the other strings S It can be estimated that the difference is small and the noise wraps around each string S1 to S4.
Therefore, in step S80, it is output that the notification means such as the display means 440 and the contact output means 450 is a trunk arc.

In step S50, when the second threshold value is calculated from the maximum value of the noise level, in the case of a string arc, as shown in FIG. 4C, the maximum value of the noise level is that the noise level of the string S1 is another string. It is 100, which is larger than S2 to S4. Therefore, the second threshold value set to 40% of the maximum value is 100 × 0.4 = 40.
Therefore, in step S60, when the second determination means 430 compares the second threshold value with the noise levels of the strings S1 to S4, the noise level of the strings S1 is larger than the second threshold value, but the noise levels of the strings S2 to S4 are higher. Each noise level is less than the second threshold.

In step S70, when the second determination means 430 determines that the number of strings having a noise level larger than the second threshold value is 1, the noise level of the string having the maximum value is larger than the noise level of the other strings. Therefore, it can be determined that an arc has occurred in the string having the maximum noise level.
In step S90, it is output that the notification means such as the display means 440 and the contact output means 450 is the string arc, and the generated string is the string S1.

In this way, the noise level of each string is measured by the measuring means 410, and by comparing these noise levels with the first threshold value indicating the arc generation, it is determined whether or not the arc is generated, and the arc is generated. If it occurs, the second determination means 430 compares it with the second threshold value in order to discriminate the relationship between the maximum value of the noise level and the noise level of another string S.
As a result, when the number of strings exceeding the second threshold value is 1, it can be determined that an arc has occurred in the string S1 having the maximum noise level.
Further, when the number of strings exceeding the second threshold value is a plurality, it can be determined that the arc is generated at a place other than each string.

In this way, a second threshold for identifying whether the noise level generated in one string is prominent or the noise level generated in the entire string is generated on average is used for each string. By identifying the relationship between the maximum value of the noise level and the noise level of another string, it is possible to determine whether it is a string arc or a trunk arc.
At this time, since the output cables of the strings S1 to S4 are not cut off, the solar cell module M of the strings S1 to S4 can continue power generation to the PCS 30.

In the first embodiment, the photovoltaic power generation system 10 is a centralized PCS-PV system having a junction box 20, but each string S1 to S4 is a multi-string PCS-PV system directly connected to the PCS. It can also be applied.

Therefore, since the arc detection device 40 only measures the noise level for each output cable of each string, it can be measured even in a photovoltaic power generation system having various configurations, without stopping the power generation by the solar cell module. , The location where the arc is generated can be specified.

[First Modified Example of Embodiment 1]
The first modification according to the first embodiment of the present invention will be described with reference to FIGS. 5 and 6. In FIG. 5, those having the same configuration as that in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.
As described above, the PCS noise level changes from operating so as to perform maximum power conversion according to the power generation status of the solar cell module M. The noise level varies depending on the PCS model, the configuration of the photovoltaic power generation system, and the discharge state of the arc. From this, if the first threshold value for detecting the arc is too low, PCS noise will also be detected, and if it is too high, the arc generation cannot be detected.

In the arc detection device 41 shown in FIG. 5, as shown in FIG. 6, if the noise level does not exceed the first threshold value in step S130, the first determination means 421 sets the counter of the corresponding string S in step S140. It resets and proceeds to step S110. However, when it is determined in step S130 that the noise level exceeds the first threshold value, the counter of the corresponding string S having the noise level exceeding the first threshold value is incremented by +1 in step S150. And.

Then, in step S160, the first determination means 421 determines whether or not the counter value has reached a predetermined number of times (third threshold value) indicating the number of consecutive times exceeding the first threshold value (continuous number of arc detections). do. The third threshold value can be, for example, 5 times.
When the counter value reaches a predetermined number of times, it is determined that an arc has been generated, and the process proceeds to the process by the second determination means 430 (processes after step S170). If the counter value has not reached the predetermined number of times, the process proceeds to step S110 in order to continuously detect arc noise.

In this way, when the number of noise levels that continuously exceed the first threshold value exceeds a predetermined number of times (third threshold value), it is determined that an arc is generated, and the accidentally generated noise is converted into arc noise due to the arc generation. It is possible to prevent erroneous detection.

In the flowchart shown in FIG. 6, steps S110 to S120 are the same as steps S10 to S20 shown in FIG. 3, and steps S170 to S220 shown in FIG. 6 are step S40 shown in FIG. Since it is the same as from step S90 to step S90, the description thereof will be omitted.

[Second Modification of Embodiment 1]
A second modification of the arc detection device according to the first embodiment of the present invention will be described with reference to FIG. In FIG. 7, those having the same configuration as that in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.
In the first modification of the first embodiment, the arc generation is determined by the fact that the counter value indicating the number of times the noise level continuously exceeds the first threshold value exceeds the third threshold value. In the second modification, the third threshold value is changed according to the measured value of the circuit current.

As shown in FIG. 7, the arc detection device 42 includes detectors 411a to 411d installed in the strings S1 to S4 (see FIG. 1) for arc detection, as well as a current measuring device 411e clamped to the trunk line. ing. Further, the arc detection device 42 includes an A / D conversion means 460 and a threshold value setting means 470.

The current measuring device 411e can be a Hall element type current sensor including a magnetic core clamped to the trunk line and a Hall element inserted into the gap portion of the magnetic core. The current measuring device 411e outputs the Hall voltage corresponding to the magnetic flux as the current flowing through the trunk line by the Hall effect of the Hall element when the magnetic flux in the magnetic core due to the current flowing through the trunk line passes through the Hall element.

The A / D conversion means 460 converts the analog signal from the current measuring device 411e into a digital signal. When the digital value corresponding to the circuit current value flowing through the trunk line converted by the A / D conversion means 460 is smaller than the predetermined value (fourth threshold value), the threshold value setting means 470 determines that the arc is generated by the first determination means 421. The set value of the number of consecutive times indicated by the third threshold value used for is set to a value increased from the initial value. For example, the third threshold value can be set to 5 to 7 or 10 times.

Further, when the circuit current measured by the current measuring device 411e is larger than a predetermined value, the threshold value setting means 470 sets a value obtained by reducing the set value of the number of consecutive times indicated by the third threshold value from the initial value. For example, the third threshold value can be set to 5 to 3 times.

When the circuit current is small, the arc current is small and the amount of heat of the arc is small. Therefore, even if the counter value indicated by the third threshold value is increased and the number of consecutive times is increased, the influence on the cable and the device is small.
Therefore, by increasing the third threshold value until the arc generation is confirmed and taking a long time until the arc generation is confirmed, the arc noise due to the arc generation can be detected firmly.

On the contrary, when the circuit current is large, the arc current is large and the amount of heat of the arc is large, so that the influence on the cable and equipment is large.
Therefore, the arc generation can be detected in a short time by reducing the third threshold value until the arc generation is confirmed and shortening the time until the arc generation is confirmed.

In the second modification, the third threshold value is the number of consecutive arc detections, but the third threshold value may be the measurement time for arc detection. When the third threshold value is set as the measurement time, the first determination means 421 detects the arc as many times as possible during the measurement time indicated by the third threshold value, and determines the arc generation when the arcs are continuously detected. do it.

Further, in the second modification, the current measuring device 411e is installed on the trunk line, but in order to accurately measure the circuit current from each of the strings S1 to S4, the strings S1 to 411d are similarly measured. It is desirable to install the current measuring device 411e on the output cables C1 to C4 of S2.

[Third variant of Embodiment 1]
A third modification of the arc detection device according to the first embodiment of the present invention will be described with reference to FIG. In FIG. 8, those having the same configuration as that in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.
In the second modification of the first embodiment shown in FIG. 7, the threshold value setting means 470 indicates a predetermined number of consecutive times exceeding the first threshold value depending on whether or not the circuit current is larger than a predetermined value (fourth threshold value). (Third threshold value) was increased or decreased, but in the third modified example shown in FIG. 8, the threshold value setting means 471 of the arc detection device 43 caused a level difference between the noise level from the measuring means 410 and the first threshold value. Based on this, the first determination means 421 increases or decreases the set value of the number of consecutive times indicated by the third threshold value used for determining the arc generation.

When the level difference between the noise level from the measuring means 410 and the first threshold value is smaller than the predetermined value (fifth threshold value), the threshold value setting means 471 sets the setting value of the number of consecutive times indicated by the third threshold value from the initial value. The value is reduced. For example, the third threshold value can be set to 5 to 3 times.

Further, when the level difference between the noise level from the measuring means 410 and the first threshold value is larger than a predetermined value (fifth threshold value), the threshold value setting means 471 initially sets the set value of the number of consecutive times indicated by the third threshold value. The value is increased from the value. For example, the third threshold value can be set to 5 to 7 or 10 times.

When the circuit current is large, the arc noise including the high frequency component propagates through the output cables C1 to C4, and the arc noise detected by the frequency analysis means 414 tends to have a low level. Therefore, the level difference between the noise level of the arc noise and the first threshold value becomes small.
On the other hand, since the circuit current is large, the arc current is large and the amount of heat of the arc is large, so that the influence on the cable and equipment is large.
Therefore, when the level difference between the noise level of the arc noise and the first threshold value is smaller than the fifth threshold value, the third threshold value until the arc generation is confirmed is reduced, and the time until the arc is confirmed is shortened. The arc generation can be detected in a short time.

When the circuit current is small, the level of arc noise detected by the frequency analysis means 414 tends to be large. Therefore, the level difference between the noise level of the arc noise and the first threshold value becomes large.
Since the circuit current is small, the arc current is small and the amount of heat of the arc is small, so the effect on cables and equipment is small.
Therefore, when the level difference between the noise level of the arc noise and the first threshold value is larger than the fifth threshold value, the third threshold value until the arc generation is confirmed is increased, and the time until the arc generation is confirmed is taken longer. As a result, arc noise due to arc generation can be detected firmly.

[Fourth Modified Example of Embodiment 1]
A fourth modification of the arc detection device according to the first embodiment of the present invention will be described with reference to FIGS. 9 to 11. In FIG. 9, those having the same configuration as that of FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.
In the fourth modification, the first threshold value is increased or decreased based on the difference between the noise level of the PCS noise measured periodically and the first threshold value.

In the fourth modification, the threshold setting means 472 shown in FIG. 9 first accumulates the noise level (PCS noise level) periodically input from the measuring means 410, excluding the noise level exceeding the first threshold. Calculate the average value. Next, the threshold value setting means 472 increases or decreases the first threshold value so that it becomes a specified value when the level difference between the average value and the first threshold value deviates from the specified value (sixth threshold value).

For example, a case where the noise level of PCS noise is low will be described with reference to FIG.
In step S210, the threshold setting means 472 periodically acquires the noise level of PCS noise from the measuring means 410, and in step S220, the threshold setting means 472 accumulates the noise level, calculates the average value, and calculates the average value. As a result of comparing the level difference between the first threshold value and the first threshold value with the specified value, since the level difference is larger than the specified value, the first threshold value is reduced so that the level difference between the average value and the first threshold value becomes the specified value.
After that, the arc generation by the first determination means 420 is detected by the new first threshold value whose level is lowered (step S230).

Next, a case where the noise level of PCS noise is low will be described with reference to FIG.
In step S310, the threshold setting means 470 periodically acquires the noise level of the PCS noise from the measuring means 410. Next, in step S320, the threshold setting means 472 accumulates the noise level, calculates the average value, and compares the level difference between the average value and the first threshold value with the specified value. As a result, the level difference is smaller than the specified value. Therefore, the first threshold value is increased so that the level difference between the average value and the first threshold value becomes a specified value.
After that, the arc generation by the first determination means 420 is detected by the new first threshold value whose level has been raised (step S330).

In this way, the noise level of the PCS noise level changes depending on the MPPT (Maximum power point tracking) control that performs maximum power conversion according to the type of PCS and the power generation status of the solar cell. However, by constantly monitoring the level of PSC noise during steady operation and increasing or decreasing the first threshold value, a threshold value for optimum judgment can be obtained, and both prevention of false detection and certainty of detection can be achieved. Can be done.

[Embodiment 2]
A photovoltaic power generation system using the arc detection device according to the second embodiment of the present invention will be described with reference to FIGS. 12 and 13. In FIG. 12, those having the same configuration as that in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

The arc detection device 45 according to the second embodiment shown in FIG. 12 is installed in the centralized PCS-PV system in the same manner as the arc detection device 40 (see FIG. 2) according to the first embodiment.

In the arc detection device 45, the second determination means 431 determines whether the arc is generated on the trunk line or each string S.
Next, the determination by the second determination means 431 will be described with reference to FIG. In FIG. 13, the determination based on the first threshold value in steps S410 to S430 is the same as in steps S10 to S30 shown in FIG. 3, so the description thereof will be omitted.

The second determination means 431 identifies the string S having the maximum value from the noise level of each string S and the string S having the second largest value (step S440).
Next, the second determination means 431 calculates the level difference between the maximum value of the noise level and the second value, and compares it with the second threshold value (step S450).
The second threshold value is a threshold value for determining the degree of the level difference between the maximum value of the noise level of the string and the second value, and can be, for example, the maximum value of the noise level × 0.6.

When the level difference between the maximum value and the second value is equal to or greater than the second threshold value, in step S460, the second determination means 431 determines that an arc has occurred in the string S in which the maximum value has been measured. do. As can be seen from the table shown in FIG. 4, if the arc is generated by any of the strings S, the level difference between the arc-generated string S and the other strings S becomes large. Therefore, it can be determined that an arc has occurred in the string S for which the maximum value has been measured.
In that case, the notification means such as the display means 440 and the contact output means 450 outputs that it is a string arc (step S470).

If the level difference is less than the second threshold value, in step S460, the second determination means 431 determines that an arc has occurred on the trunk line. This is because if the arc is generated on the trunk line, as can be seen from the table shown in FIG. 4 (A), the arc noise from the trunk line wraps around to each string S1 to S4, so that the noise of each string S The level difference becomes smaller. Therefore, it can be determined that an arc has occurred on the trunk line.
In that case, the notification means such as the display means 440 and the contact output means 450 outputs that it is a trunk arc (step S480).

In this way, the level difference between the maximum noise level and the second value is determined by using the second threshold value for discriminating the relationship between the maximum noise level of each string and the noise level of the other strings. If it is equal to or higher than the second threshold value, which is a specified value, it indicates that the noise level of the string S having the maximum value is higher than the noise level of the other strings S. Therefore, the noise level S is the maximum value of the string S. It can be determined that an arc has occurred.
Further, if the level difference is less than the second threshold value, it can be estimated that the noise level of the string S which has become the maximum value has a small difference in the noise level of the other strings S, and the noise level wraps around each string S. Therefore, it can be determined that an arc is generated at a place other than each string S, for example, a trunk line.
Therefore, the arc detection device 45 can identify the generation location without stopping the power generation by the solar cell module even in the photovoltaic power generation system having various configurations.

When the arc detection device 45 is installed in the multi-string PCS-PV system in which the strings S1 to S4 are directly connected to the PCS, the difference between the maximum noise level and the second level is equal to or greater than the second threshold value. For example, the string whose maximum value was the measured noise level.
However, if the difference between the maximum value of the noise level and the second level is less than the second threshold value, it can be determined that the arc is generated not in each string S1 to S4 but in another place such as in the PCS.

In the arc detection device 45 according to the second embodiment, the same effect can be obtained by applying the configurations of the first modification to the fourth modification of the first embodiment.

Since the arc detection device of the present invention can identify the arc generation location only by installing a measuring means for measuring the noise level for each output cable of each string, it is possible to use a centralized PCS-PV system or a multi-string PCS-PV system. Any method is suitable.

10 Photovoltaic system 20 Junction box 30 PCS
40, 41, 42, 43, 44, 45 Arc detection device 400 Device body 410 Measuring means 411, 411a to 411d Detector 411e Current measuring device 412 Switching means 413,460 A / D conversion means 414 Frequency analysis means 420,421 1 Judgment means 430, 431 Second judgment means 440 Display means 450 Contact output means 470, 471, 472 Threshold setting means M Solar cell module S, S1 to S4 String C1 to C4 output cable

Claims (7)

A measuring means for measuring the noise level from the current waveform of each output cable of each string of the solar cell module, and
The first determination means for determining the arc generation by comparing the noise level from the measuring means with the first threshold value indicating the arc generation, and
When the first determination means detects the occurrence of an arc, the noise level is the maximum value based on the second threshold value for discriminating the relationship between the maximum value of the noise level of each string and the noise level of the other strings. It is provided with a second determination means for determining whether an arc is generated in the string to be used or an arc is generated in a place other than each string.
The second determination means uses the threshold value for determining the degree of the level difference between the maximum value of the noise level of the string and the second threshold value as the second threshold value, and if the level difference is equal to or greater than the second threshold value, An arc detection device that determines that an arc has occurred in the string having the maximum noise level, and if it is less than the second threshold value, determines that an arc has occurred in a place other than the strings. A measuring means for measuring the noise level from the current waveform of each output cable of each string of the solar cell module, and
The first determination means for determining the arc generation by comparing the noise level from the measuring means with the first threshold value indicating the arc generation, and
When said first determination means detects arcing, based on the second threshold value for identifying the relationship between the noise level of the maximum value and the other strings of the noise level of each string, the second threshold value If the number of strings exceeded is 1, it is determined that an arc has occurred in the string having the maximum noise level, and if there are a plurality of strings exceeding the second threshold value, other strings other than the above-mentioned strings are determined. An arc detection device including a second determination means for determining that an arc has been generated at a location. It said second determination means, the arc detecting device according to claim 2, wherein the predetermined ratio from its maximum value of the noise level of the string shall be the second threshold value. A claim that the first determination means determines that an arc has been generated when the number of arc detections by comparing the noise level from the measurement means with the first threshold value indicating the arc generation reaches the number of times based on the third threshold value in succession. The arc detection device according to any one of 1 to 3. A current measuring device that measures the circuit current from the solar cell module, and
4. A claim 4 comprising a threshold value setting means for comparing the circuit current with a fourth threshold value, increasing the third threshold value when the circuit current is small, and decreasing the third threshold value when the circuit current is large. The arc detection device described. The level difference between the noise level from the measuring means and the first threshold value is compared with the fifth threshold value, the third threshold value is decreased when the level difference is small, and the third threshold value is large when the level difference is large. The arc detection device according to claim 4, further comprising a threshold value setting means for increasing the threshold value. When the noise level from the measuring means excluding the noise level exceeding the first threshold value is accumulated and the average value is calculated, and the level difference between the average value and the first threshold value deviates from the sixth threshold value. The arc detection device according to any one of claims 1 to 6, further comprising a threshold value setting means for increasing or decreasing the first threshold value so that the level difference becomes the sixth threshold value.

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