Arc detection device

Abstract

This arc detection device detects an arc occurring in a power line that connects a DC power supply for power generation or charging and a conversion device for converting DC power outputted from the DC power supply to AC power. The arc detection device includes a detection unit, a first arc determination unit, a suppression control unit, and a second arc determination unit. The detection unit detects information for determining the occurrence of an arc. The first arc determination unit performs primary determination of the occurrence of an arc on the basis of the result of the detection performed by the detection unit. When it is determined, in the primary determination performed by the first arc determination unit, that an arc has occurred, the suppression control unit reduces the current flowing through the power line or the voltage of the power line. In a state in which the current flowing through the power line or the voltage of the power line is reduced in response to the primary determination performed by the first arc determination unit, the second arc determination unit determines whether a current is flowing through the power line, and thereby performs secondary determination of the occurrence of an arc.

Description

Arc Detector

[0001] The present invention relates to an arc detection device.

[0002] Conventionally, arc detection devices that detect the occurrence of an arc in a solar power generation system have been known. The arc detection device disclosed in Patent Document 1 converts the output current of a solar cell string detected by a current sensor into a current power spectrum, and compares the section value of an arc measurement section, which is a predetermined frequency range in the power spectrum, with a threshold value to determine whether an arc has occurred.

[0003] JP 2016-151514 A

[0004] Arc detection devices that detect arcs that occur when a wire breaks in a solar power generation system are affected by noise that varies depending on the installation environment, and may falsely identify noise as an arc. If the frequency of false detection of arcs due to noise increases, the solar power generation system must be temporarily stopped each time a false detection occurs, resulting in a decrease in power generation efficiency.

[0005] An object of the present invention is to provide an arc detection device that can suppress erroneous detection of arc occurrence.

[0006] An arc detection device according to one aspect of the present invention detects an arc occurring in a power line connecting a DC power source that generates or charges power and a converter that converts DC power output from the DC power source into AC power. The arc detection device includes a detection unit, a first arc determination unit, a suppression control unit, and a second arc determination unit. The detection unit detects information for determining the occurrence of an arc. The first arc determination unit makes a primary determination of the occurrence of an arc based on the detection result of the detection unit. When the first arc determination unit determines that an arc has occurred in the primary determination, the suppression control unit reduces the current flowing in the power line or the voltage of the power line. The second arc determination unit makes a secondary determination of the occurrence of an arc by determining whether or not a current is flowing in the power line in a state in which the current flowing in the power line or the voltage of the power line has been reduced in accordance with the primary determination by the first arc determination unit.

[0007] This arc detection device determines the occurrence of an arc in two stages using the first arc determination unit and the second arc determination unit, thereby reducing erroneous detection of the occurrence of an arc. Furthermore, the second arc determination unit determines the occurrence of an arc by determining whether a current is flowing through the power line when the current or voltage through the power line is reduced by the suppression control unit. Therefore, for example, even if the secondary determination determines that no arc is occurring, it is possible to maintain the power supply state of a DC power supply system in which the arc detection device is installed, thereby reducing a decrease in the power generation efficiency of the DC power supply system compared to when the DC power supply system is shut down. Furthermore, since the suppression control unit reduces the current or voltage through the power line, it is possible to extinguish an arc when it is occurring by, for example, reducing the current or voltage to a value lower than the minimum current or voltage required for arc occurrence.

[0008] The second arc determination unit may determine that an arc has occurred when it determines that no current is flowing through the power line, which can reduce false detections of the occurrence of an arc.

[0009] The second arc determination unit may determine that no arc has occurred when it determines that a current is flowing in the power line. In this case, for example, it is possible to maintain the power supply state of the DC power supply system in which the arc detection device is installed, and therefore it is possible to suppress a decrease in the power generation efficiency of the DC power supply system compared to when the DC power supply system is stopped.

[0010] The suppression control unit may cancel the reduction of the current flowing in the power line or the voltage of the power line when the second arc determination unit determines that no arc has occurred in the secondary determination. In this case, for example, it is possible to quickly restore the DC power supply system in which the arc detection device is installed to a normal state, thereby suppressing a decrease in the power generation efficiency of the DC power supply system.

[0011] The suppression control unit may reduce the current flowing through the power line by switching the resistance of the circuit for the current flowing through the power line. In this case, the current flowing through the power line can be reduced with a simple configuration.

[0012] The arc detection device may further include a switching device connected to the power line. The suppression control unit may reduce the current flowing through the power line or the voltage of the power line by PWM-controlling the switching device. In this case, the current flowing through the power line or the voltage of the power line can be reduced with a simple configuration.

[0013] The suppression control unit may reduce the current flowing through the power line or the voltage of the power line to a value smaller than the lower limit of the voltage or current required to generate an arc, thereby suppressing erroneous detection of an arc.

[0014] The suppression control unit may reduce the current flowing through the power line or the voltage of the power line to a value smaller than a lower limit of the voltage or current necessary to generate an arc, which is determined according to the material of the power line, thereby further suppressing erroneous detection of an arc.

[0015] According to the present invention, it is possible to provide an arc detection device that can suppress erroneous detection of arc occurrence.

[0016] It is a schematic block diagram showing the configuration of a solar power generation system to which an arc detection device according to an embodiment is applied. It is a diagram for explaining an example of the configuration of a suppression control unit. It is a block diagram showing the configuration of a first arc detection device. It is a flowchart showing processing executed by a control unit.

[0017] Hereinafter, a solar power generation system 1 including an arc detection device according to an embodiment will be described with reference to the drawings. Fig. 1 is a block diagram schematically showing the configuration of the solar power generation system 1. The solar power generation system 1 is a system for outputting power output from at least one string including a plurality of solar cell modules to a load or a power grid.

[0018] The photovoltaic power generation system 1 includes a string 2 (an example of a DC power supply), a power conditioner 3 (an example of a conversion device), and an arc detection device 4 .

[0019] The string 2 is made up of a plurality of solar cell modules connected in series. Each solar cell module includes a plurality of solar cells connected in series. The string 2 is connected to a power conditioner 3.

[0020] The power conditioner 3 converts DC power output from the string 2 into AC power and outputs the AC power. The power conditioner 3 is connected to a power grid (not shown).

[0021] The power conditioner 3 has the same configuration as a conventional power conditioner, and includes circuits (not shown) such as a converter circuit, an inverter circuit, and a charge / discharge circuit.

[0022] The arc detector 4 detects the occurrence of an arc in the power line 6 connecting the string 2 and the power conditioner 3. The power line 6 includes a positive-side electric circuit and a negative-side electric circuit (not shown). The arc detector 4 is disposed, for example, in the output path of the string 2.

[0023] The arc detection device 4 includes a detection unit 10 , a filter 11 , an A / D conversion unit 12 , and a control unit 13 .

[0024] The detection unit 10 detects information for determining the occurrence of an arc. In this embodiment, the detection unit 10 is a current sensor that detects the current flowing in the power line 6. The detection unit 10 detects the current flowing in the power line 6 and outputs a detection signal to the control unit 13.

[0025] The filter 11 is a band-pass filter (BPF), and outputs the current detected by the detector 10 via an amplifier (not shown). The filter 11 passes only a current within a predetermined frequency range from the current output from the amplifier. The A / D converter 12 converts the analog current signal that has passed through the filter 11 into a digital signal and outputs it to the controller 13.

[0026] The control unit 13 is a functional configuration realized by the CPU, and is realized by the CPU executing a program stored in the ROM, RAM, etc. The control unit 13 is supplied with power from a control power supply (not shown). The control power supply is supplied with power from, for example, a commercial power supply. The control power supply may also be generated from power generated by a solar cell module.

[0027] The control unit 13 includes a first arc determining unit 21 , a suppression control unit 22 , and a second arc determining unit 23 .

[0028] The first arc determination unit 21 has a configuration similar to that of a conventional unit. The first arc determination unit 21 makes a primary determination of the occurrence of an arc based on the detection result of the detection unit 10. The first arc determination unit 21 performs an FFT on the digital signal output from the A / D conversion unit 12 to generate a power spectrum of the current, and uses the generated power spectrum for the primary determination of the occurrence of an arc. The first arc determination unit 21 may also use the frequency spectrum of the current signal obtained by Fourier transforming the time waveform of the current signal output from the detection unit 10 for the primary determination of the occurrence of an arc.

[0029] When first arc determiner 21 determines in the primary determination that an arc has occurred, suppression control unit 22 reduces the current flowing in power line 6 or the voltage of power line 6. For example, as shown in FIG. 2 , suppression control unit 22 reduces the current flowing in power line 6 by switching the resistance of the circuit of the current flowing in power line 6.

[0030] In detail, the arc detection device 4 includes a first switching device 15, a second switching device 16, and a resistor 17. The first switching device 15, the second switching device 16, and the resistor 17 are connected to the power line 6. The second switching device 16 and the resistor 17 are connected in parallel to the first switching device 15. When the first arc determination unit 21 determines that an arc has occurred in the primary determination, the suppression control unit 22 switches the contacts of the second switching device 16 from an open state to a closed state and switches the contacts of the first switching device 15 from a closed state to an open state, thereby switching the resistance of the circuit of the current flowing through the power line 6. Note that the suppression control unit 22 may be configured to reduce the current flowing through the power line 6 or the voltage of the power line 6 by PWM-controlling the first switching device 15. In this case, the second switching device 16 and the resistor 17 are omitted.

[0031] When suppression control unit 22 reduces the current flowing through power line 6 or the voltage of power line 6 in accordance with the primary determination by first arc determination unit 21, it reduces the current to a value smaller than the lower limit of the voltage or current required to generate an arc. More preferably, suppression control unit 22 reduces the current flowing through power line 6 or the voltage of power line 6 to a value smaller than the lower limit of the voltage or current required to generate an arc, which is determined according to the material of power line 6. When power line 6 is a copper wire and the current value is reduced, it is reduced to a value smaller than 0.5 A, for example. When power line 6 is a copper wire and the voltage value is reduced, it is reduced to a value smaller than 12 V, for example.

[0032] Second arc determination unit 23 determines whether the detection of the occurrence of an arc by first arc determination unit 21 is an erroneous detection. Second arc determination unit 23 makes a second determination of the occurrence of an arc by determining whether or not a current is flowing in power line 6 in a state in which the current flowing in power line 6 or the voltage of power line 6 is reduced in accordance with the primary determination by first arc determination unit 21. Second arc determination unit 23 makes a second determination of the occurrence of an arc by determining whether or not DC power is being output from string 2 to power conditioner 3.

[0033] The second arc determination unit 23 determines that an arc has occurred when it is determined that no current is flowing in the power line 6 in a state in which the current flowing in the power line 6 or the voltage of the power line 6 has been reduced by the suppression control unit 22 in accordance with the primary determination of the first arc determination unit 21. The second arc determination unit 23 determines that no arc has occurred (that it is noise) when it is determined that a current is flowing in the power line 6 in a state in which the current flowing in the power line 6 or the voltage of the power line 6 has been reduced in accordance with the primary determination of the first arc determination unit 21. In other words, the second arc determination unit 23 determines that the detection of the occurrence of an arc by the first arc determination unit 21 is an erroneous detection.

[0034] If the second arc determiner 23 determines in the secondary determination that no arc has occurred, the suppression controller 22 cancels the reduction in the current flowing through the power line 6 or the voltage of the power line 6 .

[0035] When the second arc determiner 23 determines that an arc has occurred through secondary determination, the controller 13 outputs an alarm signal regarding the occurrence of an arc to the outside.

[0036] 3 is a flowchart showing the processing executed by the control unit 13. In step S11, the control unit 13 acquires information for determining the occurrence of an arc from the detection unit 10. Here, the control unit 13 generates a power spectrum of the current based on the detection result of the current sensor that detects the current flowing in the power line 6.

[0037] In step S12, the control unit 13 makes a primary determination as to whether or not an arc has occurred based on the information acquired in step S11. If the control unit 13 determines in step S12 that an arc has occurred, the process proceeds to step S13.

[0038] In step S13, the control unit 13 reduces the current flowing through the power line 6 or the voltage of the power line 6. For example, as shown in Fig. 2, the current flowing through the power line 6 is reduced by switching the resistance of the circuit for the current flowing through the power line 6. Then, the process proceeds to step S14.

[0039] In step S14, the control unit 13 performs a secondary determination of the occurrence of an arc by determining whether or not a current is flowing in the power line 6. That is, in step S14, it is determined whether or not the detection of the occurrence of an arc in the first determination is an erroneous detection. If the control unit 13 determines that no current is flowing in the power line 6, it determines that an arc is occurring, and proceeds to step S15, outputting an alarm signal regarding the occurrence of an arc to the outside. If the control unit 13 determines that a current is flowing in the power line 6, it determines that an arc is not occurring, and proceeds to step S16, where it cancels the reduction of the current flowing in the power line 6 or the voltage of the power line 6, which was performed in step S13.

[0040] In the arc detection device 4 of the above-described photovoltaic power generation system 1, the occurrence of an arc is determined in two stages by the first arc determination unit 21 and the second arc determination unit 23, thereby making it possible to suppress erroneous detection of the occurrence of an arc. Furthermore, the second arc determination unit 23 determines the occurrence of an arc by determining whether or not a current is flowing through the power line 6 in a state in which the current flowing through the power line 6 or the voltage of the power line 6 is reduced by the suppression control unit 22. Therefore, for example, when it is determined in the secondary determination that an arc is not occurring, the photovoltaic power generation system 1 can be maintained in a conducting state, thereby suppressing a decrease in the power generation efficiency of the photovoltaic power generation system 1.

[0041] Furthermore, when reducing the current flowing through the power line 6 or the voltage of the power line 6, the suppression control unit 22 reduces the current flowing through the power line 6 or the voltage of the power line 6 to a value smaller than the lower limit of the voltage or current required to generate an arc, which is determined according to the material of the power line 6. This makes it possible to extinguish an arc when one is generated.

[0042] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0043] The configuration of the detection unit 10 and the determination means of the first arc determination unit 21 are not limited to those described in the above embodiment. The detection unit 10 may be a voltage sensor that detects the voltage difference between the positive and negative electric paths of the power line 6, or a power sensor that detects the power of the power line 6. The first arc determination unit 21 may make a primary determination of the occurrence of an arc based on the detection results of the voltage sensor or the power sensor. The first arc determination unit 21 may also make a primary determination of the occurrence of an arc using other conventionally known arc detection means.

[0044] 4: Arc detection device, 10: Detection unit, 21: Arc determination unit, 22: Suppression control unit, 23: Second arc determination unit

Claims

1. An arc detection device that detects an arc occurring in a power line connecting a DC power source that generates or charges power and a conversion device that converts DC power output from the DC power source into AC power, comprising: a detection unit that detects information for determining the occurrence of an arc; a first arc determination unit that makes a primary determination of the occurrence of an arc based on the detection results of the detection unit; a suppression control unit that reduces the current flowing in the power line or the voltage of the power line when it is determined in the primary determination of the first arc determination unit that an arc has occurred; and a second arc determination unit that makes a secondary determination of the occurrence of an arc by determining whether or not a current is flowing in the power line in a state where the current flowing in the power line or the voltage of the power line has been reduced in accordance with the primary determination of the first arc determination unit.

2. The arc detection device according to claim 1, further comprising: the second arc determination unit determining that an arc has occurred when it is determined that no current is flowing in the power line.

3. The arc detection device according to claim 1 or 2, wherein the second arc determination unit determines that no arc is occurring when it determines that a current is flowing in the power line.

4. The arc detection device according to claim 3, wherein the suppression control unit cancels the reduction of the current flowing through the power line or the voltage of the power line when the second arc determination unit determines in the secondary determination that no arc has occurred.

5. The arc detection device according to claim 1 or 2, wherein the suppression control unit reduces the current flowing through the power line by switching a resistance of a circuit for the current flowing through the power line.

6. The arc detection device according to claim 1 or 2, further comprising a switching device connected to the power line, wherein the suppression control unit reduces the current flowing through the power line or the voltage on the power line by PWM controlling the switching device.

7. The arc detection device according to claim 1 or 2, wherein the suppression control unit reduces the current flowing through the power line or the voltage of the power line to a value smaller than the lower limit of the voltage or current required to generate an arc.

8. The arc detection device according to claim 1 or 2, wherein the suppression control unit reduces the current flowing through the power line or the voltage of the power line to a value smaller than a lower limit value of the voltage or current required to generate an arc, the lower limit value being determined according to the material of the power line.

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