Arc detection device and system

Abstract

To provide an arc detection device capable of detecting the occurrence of an arc with high accuracy. [Solution] The arc detection device is applied to a power supply system including a DC power supply and a power line connected to the DC power supply. The arc detection device includes a sensor, a shutdown control unit, a characteristics detection unit, and an arc determination unit. The sensor is connected to the power line and detects information for determining whether an arc has occurred. The shutdown control unit controls a shutdown device connected to the power line to intentionally generate an arc. The characteristics detection unit detects frequency characteristics by frequency analyzing the output from the sensor. The arc determination unit determines whether an arc has occurred using a first frequency characteristic detected by the characteristics detection unit when no arc has occurred and a second frequency characteristic detected by the characteristics detection unit when an arc has been intentionally generated.

Description

[Technical Field]

[0001] The present invention relates to arc detection devices and systems. [Background technology]

[0002] Arc detection devices that detect the occurrence of an arc in a solar power generation system are known. The arc detection device disclosed in Patent Document 1 determines whether an arc has occurred by using frequency analysis. Specifically, the arc detection device 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-151514 Summary of the Invention [Problem to be solved by the invention]

[0004] The frequency characteristics of a solar power generation system change due to the installation environment, the installation method such as the length and routing of power lines, changes in the PV system configuration such as power conditioners, or the aging of components. When the frequency characteristics change, the accuracy of arc detection by the arc detection device decreases, and there is a risk of false detection or missed detection.

[0005] An object of the present invention is to provide an arc detection device that can accurately detect the occurrence of an arc. [Means for solving the problem]

[0006] An arc detection device according to one aspect of the present invention is applied to a power supply system including a DC power supply and a power line connected to the DC power supply. The arc detection device includes a sensor, a shutdown control unit, a characteristics detection unit, and an arc determination unit. The sensor is connected to the power line and detects information for determining whether an arc has occurred. The shutdown control unit controls a shutdown device connected to the power line to intentionally generate an arc. The characteristics detection unit performs frequency analysis of the output from the sensor to detect frequency characteristics. The arc determination unit determines whether an arc has occurred using a first frequency characteristic detected by the characteristics detection unit when no arc has occurred and a second frequency characteristic detected by the characteristics detection unit when an arc has been intentionally generated.

[0007] In this arc detection device, the arc determination unit determines the occurrence of an arc using the second frequency characteristic obtained by intentionally generating an arc using the shutdown control unit. That is, by intentionally generating an arc using the shutdown control unit, the arc determination unit can previously grasp the signal of the frequency component specific to an arc in a real environment that differs for each power supply system. This makes it possible to accurately detect an arc that occurs, for example, when a power line is broken, even if the frequency characteristics of the power supply systems differ or change.

[0008] The sensor may be a current sensor that detects the current flowing through the power line, in which case the first frequency characteristic and the second frequency characteristic can be easily detected.

[0009] The arc determination unit may set a frequency range for determining the occurrence of an arc by comparing the first frequency characteristic with the second frequency characteristic, which enables optimal arc detection according to the installation environment of the power supply system.

[0010] The interruption control unit may control the interrupting device to periodically generate an arc. The arc determination unit may periodically correct the frequency range in accordance with the control of the interrupting device by the interruption control unit. In this case, even if the frequency characteristics of the power supply system change, it is possible to detect an arc that is optimal for the installation environment of the power supply system.

[0011] The sensor may be a current sensor that detects the current flowing in the power line or a power sensor that detects the power output from the DC power supply. The interruption control unit may not execute control to intentionally generate an arc when the current value detected by the current sensor is below a certain level or the amount of power detected by the power sensor is below a certain level. In this case, it is possible to prevent the arc detection algorithm by the arc determination unit from being corrected based on the frequency characteristics detected in an abnormal state.

[0012] The characteristic detection unit may convert the output from the sensor into a power spectrum. The arc determination unit may set a predetermined threshold based on the second frequency characteristic and determine whether an arc has occurred by comparing the power spectrum with the predetermined threshold. In this case, optimal arc detection according to the installation environment of the power supply system becomes possible.

[0013] The interruption control unit may control the interrupting device to periodically generate an arc. The arc determination unit may periodically correct the predetermined threshold value in accordance with the control of the interrupting device by the interruption control unit. In this case, even if the frequency characteristics of the power supply system change, it is possible to detect an arc optimally according to the installation environment of the power supply system.

[0014] The arc determination unit may set a frequency domain for determining the occurrence of an arc by comparing the first frequency characteristic with the second frequency characteristic. The arc determination unit may determine the occurrence of an arc by comparing the power spectrum with a predetermined threshold value in the frequency domain. In this case, the arc determination sensitivity is optimized with the frequency domain optimized, thereby enabling optimal arc detection according to the installation environment of the power supply system.

[0015] A system according to another aspect of the present invention includes a DC power supply, a power line connected to the DC power supply, and the arc detection device described above. This system is capable of detecting an arc with high accuracy. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an arc detection device that can accurately detect the occurrence of an arc. [Brief explanation of the drawings]

[0017] [Figure 1] 1 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; [Figure 2] 10 is a graph showing a change in current value when an arc is intentionally generated. [Figure 3] FIG. 10 is a waveform diagram showing a power spectrum corresponding to a first frequency characteristic when no arc is generated. [Figure 4] FIG. 10 is a waveform diagram showing a power spectrum corresponding to a second frequency characteristic when an arc is intentionally generated. [Figure 5] 4 is a flowchart showing a process executed by a control unit. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a solar power generation system 1 (an example of a power supply system) 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.

[0019] 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), a power line 4, a circuit breaker 5, and an arc detection device 6.

[0020] 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.

[0021] 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).

[0022] 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.

[0023] The power line 4 connects the string 2 and the power conditioner 3. The power line 4 includes a positive-side electric circuit and a negative-side electric circuit (not shown).

[0024] The circuit breaker 5 switches between connecting and disconnecting the string 2 and the power line 4 in response to a command from the power conditioner 3 or the arc detection device 6. The circuit breaker 5 is, for example, a mechanical relay, and can switch its contacts between a closed state and an open state. When the contacts of the circuit breaker 5 are in the closed state, power is output from the string 2 to the power conditioner 3. When the contacts of the circuit breaker 5 are in the open state, the output of power from the string 2 to the power conditioner 3 is cut off.

[0025] The arc detection device 6 detects the occurrence of an arc in the power line 4 or the circuit breaker 5. The arc detection device 6 is disposed in the output path of the string 2, for example.

[0026] Arc detection device 6 includes a current sensor 10, a voltage sensor 11, a power sensor 12, a filter 13, an A / D conversion unit 14, and a control unit 15. Each of current sensor 10 and voltage sensor 11 is an example of a sensor.

[0027] The current sensor 10 detects the current flowing through the power line 4 and outputs a detection signal. The current sensor 10 detects current waveform data that indicates the waveform of the current flowing through the power line 4. The voltage sensor 11 detects the voltage difference between the positive and negative electrode paths of the power line 4. The power sensor 12 detects the power output from the string 2.

[0028] The filter 13 extracts components in the arc frequency band from the current waveform data amplified by an amplifier (not shown). The filter 13 is a band-pass filter (BPF) that passes only current within a predetermined frequency range from the current output from the amplifier.

[0029] The A / D conversion unit 14 converts the analog current signal that has passed through the filter 13 into a digital signal and outputs it to the control unit 15 .

[0030] The control unit 15 is a functional configuration realized by the CPU, and is realized by the CPU executing a program stored in the ROM, RAM, or the like. The control unit 15 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 be generated from power generated by a solar cell module.

[0031] Control unit 15 includes an FFT unit 20 (an example of a characteristic detection unit), a shutdown control unit 21, and an arc determination unit 22. FFT unit 20 detects frequency characteristics by performing frequency analysis on the output from current sensor 10. FFT unit 20 performs a fast Fourier transform on the digital signal output from A / D conversion unit 14, and calculates the power spectrum of the current waveform data for each frequency component.

[0032] The interruption control unit 21 controls the circuit breaker 5 connected to the power line 4 to intentionally generate an arc. While power is being output from the string 2 to the power conditioner 3, the interruption control unit 21 outputs a command signal to switch the contacts of the circuit breaker 5 from a closed state to an open state. This generates an arc on the power line 4 (between the contacts of the circuit breaker 5). For example, the interruption control unit 21 outputs a command signal to switch the contacts of the circuit breaker 5 from an open state after a predetermined time has elapsed since outputting the command signal to switch the contacts of the circuit breaker 5 from a closed state to an open state.

[0033] The interruption control unit 21 controls the interruption device 5 to periodically generate an arc. Fig. 2 is a graph showing changes in current value when an arc is intentionally generated by the interruption control unit 21. The interruption control unit 21 is programmed to execute control to intentionally generate an arc, for example, in the morning, afternoon, and evening every three months, or when regular maintenance, equipment renewal, or equipment change is performed on the solar power generation system 1.

[0034] When the arc determination unit 22 determines that an arc has occurred, the interruption control unit 21 outputs a command signal to switch the contacts of the interruption device 5 from a closed state to an open state. This causes the output of power from the string 2 to the power conditioner 3 to be interrupted.

[0035] The arc determination unit 22 determines the occurrence of an arc using a first frequency characteristic detected by the FFT unit 20 when no arc is occurring and a second frequency characteristic detected by the FFT unit 20 when an arc is intentionally caused to occur.

[0036] Fig. 3 is a waveform diagram showing a power spectrum corresponding to a first frequency characteristic when no arc is generated, and Fig. 4 is a waveform diagram showing a power spectrum corresponding to a second frequency characteristic when an arc is generated intentionally.

[0037] Arc determination unit 22 sets a frequency range in which to determine whether an arc has occurred by comparing the first frequency characteristic shown in Fig. 3 with the second frequency characteristic shown in Fig. 4. Based on the first frequency characteristic and the second frequency characteristic, arc determination unit 22 optimizes the frequency range in which to determine whether an arc has occurred and the frequency range in which noise reduction is performed. The frequency range in which to determine whether an arc has occurred is set, for example, to be within a predetermined range from the peak value of the power spectrum in the second frequency characteristic.

[0038] The arc determination unit 22 sets a predetermined threshold (arc determination threshold shown in FIG. 4) based on the second frequency characteristic. The arc determination unit 22 optimizes the sensitivity of the arc determination based on the second frequency characteristic. The arc determination unit 22 compares the power spectrum in the set frequency region with the predetermined threshold to determine the occurrence of an arc. The arc determination unit 22 determines that an arc has occurred when the peak value of the power spectrum in the set frequency region is equal to or greater than the predetermined threshold.

[0039] The peak value of the power spectrum changes depending on the magnitude of the DC power output from string 2. Therefore, the magnitude of the DC power output from string 2 affects the sensitivity of the arc determination by arc determination unit 22. Therefore, based on the second frequency characteristic, arc determination unit 22 sets predetermined thresholds corresponding to each of a plurality of patterns when the amount of power generated by string 2 or the value of the current flowing through power line 4 differs. For example, when the amount of power generated by string 2 is low, the peak value of the power spectrum in the set frequency range is low, so the predetermined threshold is set low to reduce the sensitivity of the arc determination.

[0040] Arc determination unit 22 periodically corrects the frequency range for determining the occurrence of an arc based on the first frequency characteristic and the second frequency characteristic detected in response to the control of circuit breaker 5 by circuit breaker control unit 21. Arc determination unit 22 periodically corrects the predetermined threshold value based on the second frequency characteristic detected in response to the control of circuit breaker 5 by circuit breaker control unit 21. In other words, the detection algorithm for arc occurrence by arc determination unit 22 is periodically corrected in response to the control of circuit breaker 5 that is periodically executed by circuit breaker control unit 21 to intentionally cause an arc.

[0041] Note that when the current value detected by current sensor 10 is below a certain level, or when the amount of power detected by power sensor 12 is below a certain level, interruption control unit 21 does not execute control to intentionally generate an arc. This makes it possible to prevent the arc generation detection algorithm by arc determination unit 22 from being corrected based on frequency characteristics detected in an abnormal state, such as when the output current of string 2 is unstable.

[0042] 5 is a flowchart showing processing executed by control unit 15. In step S11, control unit 15 detects a first frequency characteristic when no arc is occurring (a state in which power is being output from string 2 to power conditioner 3). In detail, in step S11, control unit 15 calculates a power spectrum of the current waveform data based on the detection result of current sensor 10 when no arc is occurring.

[0043] In step S12, while power is being output from string 2 to power conditioner 3, control unit 15 outputs a disconnection signal to switch the contacts of circuit breaker 5 from a closed state to an open state in order to intentionally generate an arc.

[0044] In step S13, control unit 15 detects the second frequency characteristic based on the detection result of current sensor 10 when an arc is intentionally generated. Specifically, in step S13, control unit 15 calculates the power spectrum of the current waveform data based on the detection result of current sensor 10 when an arc is intentionally generated.

[0045] In step S14, control unit 15 sets a frequency range for determining whether an arc has occurred by comparing the first frequency characteristic detected in step S11 with the second frequency characteristic detected in step S13. That is, in step S14, control unit 15 optimizes the frequency range for determining whether an arc has occurred.

[0046] In step S15, arc determination unit 22 sets a predetermined threshold based on the second frequency characteristic detected in step S13. That is, in step S15, control unit 15 optimizes the sensitivity of arc determination based on the second frequency characteristic detected in step S13. Note that control unit 15 is programmed to perform the processes of steps S11 to S15 for each time period, for example, morning, afternoon, and evening, in order to set predetermined thresholds corresponding to a plurality of patterns when the amount of power generated by string 2 or the value of current flowing through power line 4 differs.

[0047] The control unit 15 is programmed to periodically perform the processes of steps S11 to S15, and periodically correct the frequency range and the predetermined threshold value for determining the occurrence of an arc.

[0048] In the arc detection device 6 of the above-described photovoltaic power generation system 1, the arc determination unit 22 determines the occurrence of an arc using the second frequency characteristic acquired by intentionally generating an arc using the shutdown control unit 21. That is, by intentionally generating an arc using the shutdown control unit 21, the arc determination unit 22 can previously grasp the signal of the frequency component specific to an arc in the actual environment that differs for each photovoltaic power generation system 1. Then, the arc determination unit 22 optimizes the frequency range for determining the occurrence of an arc and the sensitivity of the arc determination using the second frequency characteristic, thereby enabling optimal arc detection according to the installation environment of the photovoltaic power generation system 1.

[0049] Furthermore, arc determination unit 22 periodically optimizes the frequency range for determining the occurrence of an arc and the sensitivity of arc determination in accordance with the control of circuit breaker 5, which is periodically executed by circuit breaker control unit 21 to intentionally generate an arc. Therefore, even if the frequency characteristics of photovoltaic power generation system 1 change due to a change in the configuration of the system, such as power conditioner 3, or aging of components, it becomes possible to detect an arc optimally according to the installation environment of photovoltaic power generation system 1.

[0050] 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.

[0051] The arc detection device 6 may detect the first frequency characteristic and the second frequency characteristic by performing frequency analysis on the output from the voltage sensor 11. The voltage sensor 11 and the power sensor 12 may be omitted. The circuit breaker 5 may be used only to intentionally generate an arc. For example, the photovoltaic power generation system 1 may include another circuit breaker for cutting off the output of power from the string 2 to the power conditioner 3. When the arc determination unit 22 determines that an arc has occurred, the arc determination unit 22 may output a command signal for switching the contacts of the other circuit breaker from a closed state to an open state.

[0052] When the arc detector 6 detects a change in the first frequency characteristic or a change in the second frequency characteristic, the arc detector 6 may output a signal indicating that it is time for maintenance, for example. [Explanation of symbols]

[0053] 6: Arc detection device, 10: Current sensor, 20: FFT section, 21: Interruption control section, 22: Arc determination section, 23: Second arc determination section

Claims

1. An arc detection device applied to a power supply system including a DC power supply and a power line connected to the DC power supply, a sensor connected to the power line for detecting information for determining whether an arc has occurred; a circuit breaker control unit that controls a circuit breaker connected to the power line to intentionally generate the arc; a characteristic detection unit that performs frequency analysis on the output from the sensor to detect frequency characteristics; an arc determination unit that determines the occurrence of an arc using a first frequency characteristic detected by the characteristic detection unit when the arc is not occurring and a second frequency characteristic detected by the characteristic detection unit when the arc is intentionally occurring; Equipped with Arc detection device.

2. the sensor is a current sensor that detects a current flowing through the power line; The arc detection device of claim 1 .

3. the arc determination unit compares the first frequency characteristic with the second frequency characteristic to set a frequency range in which to determine the occurrence of an arc. The arc detection device of claim 1 .

4. the interruption control unit controls the interruption device to periodically generate the arc; the arc determination unit periodically corrects the frequency range in response to control of the circuit breaker by the circuit breaker control unit.

4. The arc detection device of claim 3.

5. the sensor is a current sensor that detects a current flowing through the power line or a power sensor that detects power output from the DC power supply, the interruption control unit does not execute control to intentionally generate the arc when the current value detected by the current sensor is equal to or less than a certain level or the amount of power detected by the power sensor is equal to or less than a certain level.

5. The arc detection device of claim 4.

6. the characteristic detection unit converts the output from the sensor into a power spectrum; the arc determination unit sets a predetermined threshold based on the second frequency characteristic, and determines the occurrence of an arc by comparing the power spectrum with the predetermined threshold. The arc detection device of claim 1 .

7. the interruption control unit controls the interruption device to periodically generate the arc; the arc determination unit periodically corrects the predetermined threshold value in response to control of the circuit breaker by the circuit breaker control unit.

7. The arc detection device of claim 6.

8. the arc determination unit compares the first frequency characteristic with the second frequency characteristic to set a frequency range in which to determine the occurrence of an arc; the arc determination unit compares the power spectrum with the predetermined threshold value in the frequency domain to determine the occurrence of an arc.

7. The arc detection device of claim 6.

9. A DC power supply; a power line connected to the DC power source; a circuit breaker connected to the power line; The arc detection device according to any one of claims 1 to 8; A system comprising:

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