JP2015002606A - Dc arc detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the occurrence of DC arc without influencing a circuit being a monitoring target.SOLUTION: A determination circuit 18 detects that series DC arc occurs at a point upstream of an AC component extraction circuit 11 if a voltage change component Vac is lower than a threshold value Vth2 and higher than a threshold value Vth3 and loudness of high frequency noise exceeds a threshold value Vth4 over dead time t0 and time t1. The determination circuit 18 detects the occurrence of parallel DC arc if the voltage change component Vac is lower than the threshold value Vth3 and loudness of the high frequency noise exceeds the threshold value Vth4 over the dead time t0 and the time t1. The determination circuit 18 detects that the series DC arc occurs at a position downstream of the AC component extraction circuit 11 if the voltage change component Vac is a positive value lower than the threshold value Vth1 and loudness of the high frequency noise exceeds the threshold value Vth4 for time t2.

Description

  The present invention relates to a DC arc detection device that detects the generation of a direct current (DC) arc generated in, for example, a photovoltaic generator (PV) for circuit protection.

  In recent years, the use of natural energy has been activated, and a large number of solar power generation devices such as home-use solar power generation devices and mega solar power generation facilities have been introduced. Accordingly, a fire accident caused by a DC arc generated in the solar power generation apparatus has been regarded as a problem. In the United States, NEC 690.11 was standardized as a US electrical work standard, and it was obliged to mount a device capable of detecting and protecting a DC arc in a photovoltaic power generation apparatus. In the future, similar standards will be established and implemented in Japan and Europe.

  There are two types of DC arcs: a series DC arc and a parallel DC arc. The series DC arc is generated mainly when a part such as a screw included in the current path is loosened due to a tightening failure at the time of installation or vibration for many years, and a contact failure (discontinuous section) occurs in the current path. A parallel DC arc occurs when the positive and negative power wires are corroded or when the positive and negative core wires are exposed to contact each other (short circuit) when the animal is bitten, and then the positive and negative core wires are separated. In the case of an alternating current (AC) power supply, there are moments when the current periodically becomes 0, and the arc is extinguished at this time. On the other hand, in the case of a DC power supply, current always flows, so that the arc is generated for a long period of time, so that there is a higher possibility that an arc will be generated at a high temperature, resulting in an accident that may ignite and burn. Become.

  A circuit breaker generally used for circuit protection detects an overcurrent and interrupts the circuit. However, in a photovoltaic power generation device, the power that can be generated is limited, so even if a series DC arc occurs, the current hardly changes from the normal state, and a parallel DC arc occurs and the circuit is short-circuited. However, a large short circuit current does not flow. Therefore, in the photovoltaic power generation apparatus, even if a series DC arc or a parallel DC arc is generated, no overcurrent that can be detected by the circuit breaker is generated.

  In order to detect a DC arc, a method of measuring a DC voltage of a positive and negative power supply line (hereinafter referred to as “PV line”) to which an output voltage of a photovoltaic power generator is applied is conventionally known. For example, Patent Document 1 discloses a method of detecting the occurrence of a DC arc when a DC voltage applied to a load falls below a threshold value for a certain time.

JP 2005-503743 A

J. Johnson, et al., "PHOTOVOLTAIC DC ARC FAULT DETECTOR TESTING AT SANDIA NATIONAL LABORATORIES", Photovoltaic Specialists Conference (PVSC), 2011 37th IEEE, pp. 3614-3619, June 19-24, 2011.

  However, when the DC voltage of the PV line is directly detected, the PV line and the DC arc detector cannot be electrically insulated. For this reason, when a short circuit occurs due to the failure of the DC arc detection device, it affects other devices (solar power generation devices, power conditioners, etc.) connected to the PV line. Will be affected.

  It is known to use a transformer to electrically insulate a circuit. However, even if the DC arc detector is connected to the PV line via a transformer, the magnitude of the DC voltage of the PV line cannot be detected, and the method of Patent Document 1 cannot be applied. Therefore, there is a need for a DC arc detector that can detect the occurrence of a DC arc even when the circuit to be monitored is electrically isolated.

  In addition, a DC arc is also generated when the circuit breaker in the circuit is closed and opened. In contrast to this DC arc, it is possible to detect only the occurrence of a DC arc due to circuit contact failure or short circuit. A DC arc detector is required.

  Further, there is a need for a DC arc detection device that can detect only the occurrence of a DC arc in distinction from circuit noise.

  An object of the present invention is to solve the above-described problems and to provide a DC arc detection device capable of detecting the occurrence of a DC arc with high accuracy without affecting the circuit to be monitored.

According to the DC arc detection device according to the aspect of the present invention,
In a DC arc detection device that connects a voltage source having a DC voltage and a load device via two cables, is connected in parallel between the voltage source and the load device, and detects the occurrence of a DC arc. The DC arc detector is
A voltage change component that is AC-coupled in parallel via a transformer between the voltage source and the load device and extracts a voltage change component from a predetermined reference voltage from the line voltage between the two cables. Extraction means;
Voltage rise detection means for detecting that the voltage change component has exceeded a positive first threshold;
A small voltage drop detecting means for detecting that the voltage change component has fallen below a negative second threshold;
A large voltage drop detecting means for detecting that the voltage change component has fallen below a negative third threshold value lower than the second threshold value;
First noise detecting means for detecting that the magnitude of the high-frequency noise included in the voltage change component exceeds a fourth threshold value over a predetermined dead time and a predetermined first time; ,
Second noise detection means for detecting that the magnitude of the high-frequency noise contained in the voltage change component exceeds the fourth threshold value over a predetermined second time;
DC arc generation is detected based on a combination of detection results of the voltage rise detection means, the voltage drop detection means, the voltage drop detection means, the first noise detection means, and the second noise detection means. Determination means for
(A) When the voltage change component is lower than the second threshold and higher than the third threshold, and the magnitude of the high-frequency noise is the dead time and the first When the fourth threshold is exceeded over time, detecting that a series DC arc has occurred on the side where the voltage source is located relative to the DC arc detector;
(B) When the voltage change component becomes a positive value lower than the first threshold, and the magnitude of the high-frequency noise exceeds the fourth threshold over the second time. And detecting that a series DC arc is generated on the side where the load device is located with respect to the DC arc detection device,
(C) When the voltage change component becomes lower than the third threshold, and the magnitude of the high frequency noise exceeds the fourth threshold over the dead time and the first time. It is characterized by detecting that a parallel DC arc has occurred.

  According to the DC arc detector of the present invention, it is possible to detect the occurrence of a DC arc with high accuracy without affecting the circuit to be monitored.

It is a block diagram which shows the structure of the solar energy power generation system and DC arc detection apparatus which concern on Embodiment 1 of this invention. It is a circuit diagram which shows the detailed calibration of AC component extraction circuit 11 of FIG. It is a timing chart which shows the change of voltage Vdc1, Vac, Vdc2 when the circuit breaker 2 of FIG. 1 closes. It is a timing chart which shows the change of voltage Vdc1, Vac, Vdc2 when the circuit breaker 2 of FIG. 1 opens. 3 is a timing chart showing changes in voltages Vdc1, Vac, and Vdc2 when a series DC arc occurs upstream of the AC component extraction circuit 2 in FIG. 3 is a timing chart showing changes in voltages Vdc1, Vac, and Vdc2 when a series DC arc is generated downstream of the AC component extraction circuit 2 in FIG. 3 is a timing chart showing changes in voltages Vdc1, Vac, and Vdc2 when a parallel DC arc occurs upstream or downstream of the AC component extraction circuit 2 of FIG. It is a table | surface which shows the determination result by the determination circuit 18 of FIG. It is a block diagram which shows the structure of the solar energy power generation system and DC arc detection apparatus which concern on Embodiment 2 of this invention. It is a block diagram which shows the structure of the solar energy power generation system and DC arc detection apparatus which concern on a comparative example. 11 is a timing chart showing changes in voltages Vdc1, Vac, and Vdc2 when the circuit breaker 2 in FIG. 10 is closed. It is a timing chart which shows the change of voltage Vdc1, Vac, Vdc2 when the circuit breaker 2 of FIG. 10 opens. 11 is a timing chart showing a change in voltage Vdc when a series DC arc is generated upstream of the AC component extraction circuit 2 in FIG. 10. 11 is a timing chart showing a change in voltage Vdc when a series DC arc is generated downstream of the AC component extraction circuit 2 in FIG. 10. 11 is a timing chart showing a change in voltage Vdc when a parallel DC arc occurs upstream or downstream of the AC component extraction circuit 2 of FIG. 10. 4 is a graph showing IV characteristics of the solar power generation device 1.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, similar components are designated by the same reference numerals.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of a photovoltaic power generation system and a DC arc detection device according to Embodiment 1 of the present invention. The solar power generation system includes a solar power generation device 1 and a power conditioner 3 connected via positive and negative power lines (PV lines), and a breaker 2 is provided on the PV cable. The solar power generation device 1 functions as a voltage source that supplies a DC voltage (PV line voltage) Vdc1 onto the PV line. The DC arc detection device includes an AC component extraction circuit 11, a voltage rise detection circuit 12, a voltage drop detection circuit 13, a voltage drop detection circuit 14, a rectifier circuit 15, an event noise detection circuit 16, a constant noise detection circuit 17, and A determination circuit 18 is provided.

  The AC component extraction circuit 11 is connected in parallel to the PV line between the photovoltaic power generator 1 and the power conditioner 3 (between the circuit breaker 2 and the power conditioner 3 in FIG. 1). Hereinafter, in this specification, the side where the photovoltaic power generation device 1 and the circuit breaker 2 are positioned with respect to the AC component extraction circuit 11 is referred to as “upstream”, and the power conditioner 3 is positioned with respect to the AC component extraction circuit 11. The side is called “downstream”. The AC component extraction circuit 11 is AC-coupled to the PV line, and extracts a voltage change component Vac from a predetermined reference voltage from the PV line voltage Vdc1. FIG. 2 is a circuit diagram showing a detailed configuration of the AC component extraction circuit 11 of FIG. The AC component extraction circuit 11 includes two capacitors C, a transformer TR, and a resistor R. Capacitor C is inserted to block the DC component of the voltage applied to the primary winding of transformer TR. If the capacitor C is not inserted, the + side and the − side of the PV line are short-circuited by the DC component of the voltage. The transformer TR can extract only the voltage change component Vac included in the PV line voltage Vdc1 while electrically insulating the part other than the AC component extraction circuit 11 in the DC arc detection device and the photovoltaic power generation system. it can. The resistor R is a load resistor for detecting the potential. The PV line voltage Vdc1 is usually 80V to 1000V. When the circuit breaker 2 is opened or closed, or when a DC arc is generated, a voltage almost equal to the PV line voltage Vdc1 is applied to the transformer TR for a short time, but a large current flows. The detection device can be destroyed. Therefore, a varistor or the like may be provided in the AC component extraction circuit 11 in order to protect the circuit. At this time, the saturation voltage of the varistor is set to a value higher than the cathode fall voltage (for example, 10 to 15 V) generated by the DC arc and lower than the lowest value (for example, 80 V) of the PV line voltage Vdc1. As a result, the withstand voltage of the subsequent circuit can be lowered than that of the transformer TR, and the requirements for designing the subsequent circuit can be relaxed.

  The voltage rise detection circuit 12 detects that the voltage change component Vac has exceeded a preset positive threshold value Vth1. This threshold value Vth1 will be described later.

  The small voltage drop detection circuit 13 detects that the voltage change component Vac has fallen below a preset negative threshold value Vth2. This threshold value Vth2 will be described later.

  The large voltage drop detection circuit 14 detects that the voltage change component Vac has fallen below a preset negative threshold Vth3 that is lower than the threshold Vth2. This threshold value Vth3 will be described later.

  The rectifier circuit 15 performs preprocessing for detecting high-frequency noise (DC arc noise) generated by a DC arc. The rectifier circuit 15 amplifies the voltage change component Vac, performs full-wave rectification, and outputs it as a DC voltage Vdc2. The DC voltage Vdc2 represents the magnitude of the high frequency noise included in the voltage change component Vac. By performing full-wave rectification, the voltage of the voltage change component Vac is converted to its absolute value. The rectifier circuit 15 may further include a low-pass filter for smoothing.

  The event noise detection circuit 16 detects that the small voltage drop detection circuit 13 detects that the voltage change component Vac has fallen below the threshold value Vth2, or that the voltage change component Vac has fallen below the threshold value Vth3. Is activated when the voltage drop detecting circuit 14 detects the magnitude of the high-frequency noise contained in the voltage change component Vac based on the PV line voltage Vdc1. The event noise detection circuit 16 waits for a preset dead time t0 after the activation, and then when the magnitude of the high frequency noise exceeds a preset threshold value Vth4 over a preset time t1. In addition, the occurrence of DC arc noise is detected. The event-time noise detection circuit 16 determines that the magnitude of the high frequency noise exceeds the threshold value Vth4 over the time t1 when the magnitude of the high frequency noise exceeds the threshold value Vth4 over a certain continuous or discontinuous time in the time t1. Judgment may be made to detect the occurrence of DC arc noise. The dead time t0 and the time t1 will be described later. As the threshold value Vth4, a predetermined value may be set, or a value more than three times the standard deviation may be set based on a moving average value in a normal state.

  The constant noise detection circuit 17 always detects the magnitude of the high frequency noise included in the voltage change component Vac based on the PV line voltage Vdc1. The constant noise detection circuit 17 detects the occurrence of DC arc noise when the magnitude of the high frequency noise exceeds the threshold value Vth4 over a preset time t2. The constant noise detection circuit 17 determines that the magnitude of the high-frequency noise has exceeded the threshold value Vth4 over the time t2 when the magnitude of the high-frequency noise has exceeded the threshold value Vth4 over a continuous or discontinuous period of time t2. Then, the occurrence of DC arc noise may be detected. The time t2 will be described later.

  According to Non-Patent Document 1, when a DC arc is generated, high frequency noise appears over a frequency of 1 Hz to 100 kHz, and this high frequency noise exists as long as the DC arc continues. Of this frequency, the frequency band above about 1 kHz is less affected by the inverter noise caused by the power conditioner 3.

  The determination circuit 18 generates a DC arc based on a combination of detection results of the voltage rise detection circuit 12, the voltage drop detection circuit 13, the voltage drop detection circuit 14, the event noise detection circuit 16, and the constant noise detection circuit 17. Is detected. Details of the detection method will be described later.

  Here, with reference to FIGS. 10-16, operation | movement of the DC arc detection apparatus of a general comparative example is demonstrated.

  FIG. 10 is a block diagram illustrating a configuration of a photovoltaic power generation system and a DC arc detection device according to a comparative example. The solar power generation system of FIG. 10 includes a solar power generation device 1, a circuit breaker 2, and a power conditioner 3, similarly to the solar power generation system of FIG. 1. The solar power generation device 1 functions as a voltage source that supplies a DC voltage Vdc onto the PV line. The DC arc detection device in FIG. 10 includes a voltage detection circuit 21 and a determination circuit 22. The voltage detection circuit 21 is not AC-coupled to the PV line like the AC component extraction circuit 11 of FIG. 2, but directly detects the DC voltage of the PV line.

  As a factor for changing the DC voltage Vdc of the PV line, there is an opening / closing operation of the circuit breaker 2. The circuit breaker 2 is usually mounted to electrically connect or disconnect the PV line during construction or accidents.

  FIG. 11 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when the circuit breaker 2 in FIG. 10 is closed. When the circuit breaker 2 is closed, the contact finally comes into contact with chattering, and the DC voltage Vdc of the PV line rises to the output voltage of the photovoltaic power generator 1. Therefore, when the DC voltage Vdc exceeds a threshold value Vth11 lower than the output voltage of the photovoltaic power generator 1 over a certain time t11, the closing of the circuit breaker 2 is detected.

  FIG. 12 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when the circuit breaker 2 in FIG. 10 is opened. When the circuit breaker 2 is opened, the DC voltage Vdc of the PV line becomes 0V. In order to detect that the DC voltage Vdc has become 0V, when the DC voltage Vdc becomes lower than the threshold value Vth12 (Vth12> 0) for a certain time t12, the circuit breaker is detected to be open.

  FIG. 13 is a timing chart showing changes in the voltage Vdc when a series DC arc occurs upstream of the AC component extraction circuit 2 in FIG. At the instant when the series DC arc is generated (ie, when the discontinuous section is generated in the current path), the DC voltage Vdc of the PV line rapidly decreases over a width of 10 to 15V. This voltage drop of 10 to 15 V is a cathode fall voltage when a DC arc is generated. The voltage decrease width varies depending on the length of the discontinuous section of the current path. In the photovoltaic power generation system, since it is assumed that a DC arc is generated due to the loosening of the screw, it is considered that the fluctuation of the voltage drop is slightly larger than 10 to 15V. Further, the speed of the time variation of the voltage drop width is slower than the rapid change of the voltage at the moment when the DC arc is generated. In FIG. 13, for simplicity of explanation, the DC voltage Vdc is shown not to change after the DC arc is generated. The same applies to the subsequent drawings. The occurrence of a DC arc upstream of the AC component extraction circuit 2 can be detected when the DC voltage Vdc is lower than the threshold voltage Vth13 lower than the output voltage of the photovoltaic power generator 1 for a certain time t13. . The threshold value Vth13 is set so as to distinguish between the output voltage of the photovoltaic power generation apparatus 1 and a voltage lower by 10 to 15V than the voltage. The reason why the constant time t13 is necessary is to remove the influence of noise.

  FIG. 14 is a timing chart showing changes in the voltage Vdc when a series DC arc occurs downstream of the AC component extraction circuit 2 of FIG. When the DC arc is generated, the voltage applied to the power conditioner 3 decreases by 10 to 15V. Since this drop is abrupt, the load control of the power conditioner 3 cannot follow, and it is considered that the load is constant when the DC arc is generated. FIG. 16 is a graph showing IV characteristics of the solar power generation device 1. The power conditioner 3 controls the load so that the maximum power can be taken out in the IV characteristics of the photovoltaic power generator 1. In FIG. 16, it is assumed that the maximum power can be taken out at point A. When the DC arc voltage is generated, the voltage applied to the power conditioner 3 is reduced. Therefore, the output current of the solar power generation device 1 decreases instantaneously. Then, since the operating point moves from the point A to the point B due to the decrease in the current in the IV characteristics of FIG. 16, the output voltage of the photovoltaic power generator 1 increases. Although the output voltage rises depending on the magnitude of the output current and the specifications of the photovoltaic power generator 1, it is about 10V. Since the output voltage of the photovoltaic power generator 1 has a transient characteristic, the output voltage does not increase instantaneously, but the increase rate is sufficiently faster than changes due to the amount of solar radiation. Therefore, the occurrence of the DC arc downstream of the AC component extraction circuit 2 is that the DC voltage Vdc increases from the normal output voltage of the photovoltaic power generator 1 and becomes higher than the threshold value Vth14 within a predetermined time t14. When can be detected. The threshold value Vth13 is set so as to distinguish between the normal output voltage of the photovoltaic power generation apparatus 1 and a voltage about 10 higher than the voltage.

  FIG. 15 is a timing chart showing a change in the voltage Vdc when a parallel DC arc occurs upstream or downstream of the AC component extraction circuit 2 of FIG. Whether a parallel DC arc is generated upstream of the AC component extraction circuit 2 or a parallel DC arc is generated downstream, the DC voltage Vdc of the PV line varies in the same manner. When the parallel DC arc is generated, the DC voltage Vdc of the PV line rapidly decreases to about 10 to 15V. Therefore, the occurrence of the parallel DC arc can be detected when the DC voltage Vdc is within the range of the two threshold values Vth12 and Vth15 over a certain time t15. One threshold value Vth12 is a threshold value for distinguishing the circuit breaker 2 from opening (see FIG. 12). The other threshold value Vth15 is a threshold value that is higher than the threshold value Vth12 and that detects a sudden drop in voltage.

  As described with reference to FIGS. 10 to 16, if the DC voltage Vdc of the PV line can be detected, the DC voltage Vdc is compared with a threshold value over a certain period of time, so that it can be distinguished from the opening / closing operation of the circuit breaker 2. A DC arc can be detected.

  However, when the DC arc detection device is AC-coupled to the PV line as in the AC component extraction circuit 11 of FIG. 2, the method described with reference to FIGS. 10 to 16 cannot be applied. If the DC voltage Vdc cannot be detected, a DC arc must be detected based solely on the PV line voltage change. However, in the method described with reference to FIGS. 10 to 16, when the circuit breaker 2 is opened, the DC voltage Vdc becomes 0V, and when a parallel DC arc occurs, the DC voltage Vdc becomes 10-15V. These can be distinguished simply by using a threshold value, but cannot be distinguished if the DC voltage of the PV line cannot be detected. In addition, the DC voltage is detected over a certain period of time in order to remove noise. However, when only the change in the DC voltage is extracted, it is impossible to distinguish between noise and DC arc.

  Hereinafter, the operation of the DC arc detection device of FIG. 1 will be described.

  FIG. 3 is a timing chart showing changes in the voltages Vdc1, Vac and Vdc2 when the circuit breaker 2 of FIG. 1 is closed. When the circuit breaker 2 is closed, the contact finally comes into contact with chattering. Since the contact and separation of the contacts are repeated during chattering, arc generation and arc extinction are repeated in a short time. Therefore, the magnitude of the high frequency noise exceeds the threshold value Vth4 for at least the chattering time. However, since this is not high-frequency noise caused by a DC arc at the time of an accident, it is desirable not to detect it as a DC arc. Therefore, the dead time t0 is set to a value equal to or longer than the chattering time when the circuit breaker 2 is closed. Usually, chattering time is 100 milliseconds or less. Further, in order to detect that the circuit breaker 2 is closed, a threshold value Vth1 for detecting contact of the contact of the circuit breaker 2 is set in the voltage rise detection circuit 12, and the voltage large drop detection circuit 14 is cut off. A threshold value Vth3 for detecting separation of the contacts of the device 2 is set.

  FIG. 4 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when the circuit breaker 2 of FIG. 1 is opened. When the circuit breaker 2 is opened, the PV line voltage Vdc1 becomes 0V. However, since the circuit breaker 2 is miniaturized and the distance between the contacts is short, an arc is generated after the contacted contacts are separated by opening. If this arc is an AC power source, there is a moment when the current becomes zero, so the arc will eventually extinguish, but the DC power source will continue the arc. If the arc is sustained, the arc location becomes hot and there is a possibility of burning, so the circuit breaker 2 has a mechanism for extinguishing the arc within a certain time. Normally, the arc is extinguished within 100 milliseconds. However, since this arc is not caused by an accident, it is desirable not to detect it as a DC arc. Therefore, the dead time t0 is set to a value equal to or longer than the time (100 milliseconds) during which the arc of the circuit breaker 2 is extinguished when the circuit breaker 2 is opened. When the circuit breaker 2 is opened, the voltage change component Vac has a waveform as shown in the middle stage of FIG. Since the opening of the circuit breaker 2 is detected, the threshold value Vth3 is set to a threshold value that can detect that the PV line voltage Vdc1 becomes 0V, but also detects a voltage drop of a parallel DC arc described later. A threshold value is set so that the voltage drop of the parallel DC arc can be detected and the series DC arc is not detected. As described above, the threshold value Vth3 for detecting the separation of the contacts of the circuit breaker 2 is set in the large voltage drop detection circuit 14. Since the large voltage drop detection circuit 14 also detects a voltage drop of a parallel DC arc, which will be described later, the threshold value Vth3 can be set so as to detect a voltage drop of the parallel DC arc and not to detect a series DC arc. .

  FIG. 5 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when a series DC arc is generated upstream of the AC component extraction circuit 2 in FIG. When a series DC arc is generated upstream of the AC component extraction circuit 2, the PV line voltage Vdc1 decreases by about 10 to 15V. At this time, the voltage change component Vac becomes a signal as shown in the middle of FIG. The constants of the respective elements included in the AC component extraction circuit 11 are adjusted so that the extracted AC voltage component does not oscillate and becomes a signal that only represents a steep change. The threshold value Vth2 is set so as to detect a steep voltage drop of 10 to 15V. When it is detected that the voltage change component Vac has fallen below the threshold value Vth2 or Vth3, the event noise detection circuit 16 is activated. The event noise detection circuit 16 waits for the dead time t0, and then detects the occurrence of DC arc noise when the magnitude of the high frequency noise exceeds the threshold value Vth4 for the time t1. The DC voltage Vdc2 is acquired by performing large amplification on the voltage change component Vac so that it can be detected even with DC arc noise of several mV level, and may be saturated. Therefore, the dead time t0 is set in order to wait for a time until the DC voltage Vdc2 settles near 0V. This time is appropriately set according to the magnitude of the voltage change component Vac, the magnitude of the DC voltage Vdc2, the amplification factor of the amplifier in the rectifier circuit 15, the power supply voltage, and the like. Further, the dead time t0 is set longer than the arc time generated when the above-described circuit breaker 2 is opened. The time t1 is set to a value of about 10 milliseconds or more. In order to reduce the influence of noise other than DC arc noise, a long time t1 may be set. However, if the time is too long, the detection time is extended. Therefore, a value up to about 100 milliseconds is an appropriate value. The event noise detection circuit 16 determines that the magnitude of the high frequency noise exceeds the threshold value Vth4 over the time t1 when the magnitude of the high frequency noise exceeds the threshold value Vth4 over a continuous or discontinuous time of about 90% of the time t1. The occurrence of DC arc noise may be detected.

  FIG. 6 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when a series DC arc is generated downstream of the AC component extraction circuit 2 in FIG. When a series DC arc is generated downstream of the AC component extraction circuit 2, the PV line voltage Vdc1 rises by about 10V. The change in the voltage change component Vac corresponding to this increase is at a level that cannot be detected by the threshold value Vth1. Since the time t2 longer than the duration of the arc generated when the circuit breaker 2 is opened and closed is set in the constant noise detection circuit 17, the constant noise detection circuit 17 detects only the DC arc at the time of the accident. Detect.

  FIG. 7 is a timing chart showing changes in the voltages Vdc1, Vac, and Vdc2 when a parallel DC arc is generated upstream or downstream of the AC component extraction circuit 2 of FIG. When the parallel DC arc is generated, the PV line voltage Vdc1 suddenly becomes about 10 to 15V. The threshold value Vth3 is set so that a voltage drop of (PV line voltage Vdc1 before arc occurrence) − (10 to 15V) can be detected. The large voltage drop detection circuit 14 detects that the voltage change component Vac has become lower than the threshold value Vth3.

  FIG. 8 is a table showing the determination results by the determination circuit 18 of FIG. When each detection circuit in FIG. 1 detects an event, “◯” is indicated, and when it is not detected, “−” is indicated. When the voltage change component Vac is lower than the threshold value Vth2 and higher than the threshold value Vth3, and the magnitude of the high frequency noise exceeds the threshold value Vth4 over the dead time t0 and the time t1, the determination circuit 18 When this occurs, it is detected that a series DC arc has occurred upstream of the AC component extraction circuit 11. When the voltage change component Vac becomes lower than the threshold value Vth3 and the magnitude of the high frequency noise exceeds the threshold value Vth4 over the dead time t0 and the time t1, the determination circuit 18 determines that the parallel DC arc is Detect what happened. When the voltage change component Vac becomes a positive value lower than the threshold value Vth1 and the magnitude of the high frequency noise exceeds the threshold value Vth4 over time t2, the determination circuit 18 determines that the AC component extraction circuit 11 detects that a series DC arc has occurred downstream. When the voltage change component Vac alternately exceeds the threshold value Vth1 and lower than the threshold value Vth3, the determination circuit 18 determines the length of time during which the magnitude of the high frequency noise exceeds the threshold value Vth4. When the dead time does not exceed the dead time t0, the closing of the circuit breaker 2 is detected. When the voltage change component Vac becomes lower than the threshold value Vth3 and the length of time during which the magnitude of the high frequency noise exceeds the threshold value Vth4 does not exceed the dead time t0, the determination circuit 18 Detects opening of 2. By combining the output results of the respective detection circuits in this way, it is possible to determine the series DC arc, the parallel DC arc, the circuit breaker opening and closing. In addition, it is possible to determine whether the series DC arc is generated upstream or downstream.

  With the configuration of the first embodiment, the PV line and the DC arc detection device can be insulated, and the series DC arc and the parallel DC arc are detected without being affected by the operation of the circuit breaker opening and closing. be able to. Further, since it is possible to determine whether the series DC arc is generated upstream or downstream, it is possible to narrowly specify the range of the occurrence location when the DC arc accident occurs, and to shorten the search time.

  Further, the detection result of the first embodiment can be used for alarming, or the breaker 2 can be turned off when a DC arc accident occurs.

  Moreover, since the opening / closing of the circuit breaker 2 can be detected, the work of the circuit breaker 2 can be confirmed remotely.

Embodiment 2. FIG.
FIG. 9 is a block diagram showing the configuration of the photovoltaic power generation system and the DC arc detection device according to Embodiment 2 of the present invention. In the second embodiment, the current detection circuit 19 that detects the DC current flowing in the PV line is newly provided in the DC arc detection device of the first embodiment. The determination circuit 18A of FIG. 9 operates based on the detection result of the current detection circuit 19 in addition to the operation of the determination circuit 18 of FIG. When a parallel DC arc is generated upstream of the current detection circuit 19, the current detection circuit 19 does not detect current but detects that it is generated downstream.

  As the current detection circuit 19, a current sensor using a flux gate type, a Hall effect type, a magnetic resistance type, or the like capable of detecting a DC current is used. These are current sensors that can be electrically insulated from the PV line.

  The determination circuit 18A in FIG. 9 determines whether the DC arc noise has occurred in the same manner as the determination circuit 18 in FIG. 1, and based on the detection result of the current detection circuit 19, the determination circuit 18A It is possible to determine whether it occurred or occurred downstream. When the voltage change component Vac becomes lower than the threshold value Vth3, and when the magnitude of the high frequency noise exceeds the threshold value Vth4 over the dead time t0 and the time t1, the determination circuit 18A and the PV line When a current is flowing through, a parallel DC arc is detected downstream. When the voltage change component Vac becomes lower than the threshold value Vth3, and when the magnitude of the high frequency noise exceeds the threshold value Vth4 over the dead time t0 and the time t1, the determination circuit 18A and the PV line When no current is flowing through it, it is detected that a parallel DC arc has occurred upstream.

Summary.
Three thresholds are provided for a signal that changes rapidly with respect to the AC voltage, and a means for detecting DC arc noise when a DC arc is generated is provided. The arc was discriminated. As a result, the PV line and the DC arc detection device can be insulated, and the DC DC arc and the parallel DC arc can be detected only by the AC voltage without being affected by the switching operation of the circuit breaker. In addition, it is possible to detect whether a DC arc has occurred upstream or downstream.

  Further, by providing the current detection means, it is possible to detect the upstream side and the downstream side of the parallel DC arc.

  According to the DC arc detector of the present invention, it is possible to detect the occurrence of a DC arc with high accuracy without affecting the circuit to be monitored.

DESCRIPTION OF SYMBOLS 1 Solar power generation device, 2 Circuit breaker, 3 Power conditioner, 11 AC component extraction circuit, 12 Voltage rise detection circuit, 13 Voltage drop detection circuit, 14 Voltage drop detection circuit, 15 Rectification circuit, 16 Noise detection at event Circuit, 17 Constant noise detection circuit, 18, 18A judgment circuit, 19 Current detection circuit, C capacitor, R resistance, TR transformer.

Claims (8)

In a DC arc detection device that connects a voltage source having a DC voltage and a load device via two cables, is connected in parallel between the voltage source and the load device, and detects the occurrence of a DC arc. The DC arc detector is
A voltage change component that is AC-coupled in parallel via a transformer between the voltage source and the load device and extracts a voltage change component from a predetermined reference voltage from the line voltage between the two cables. Extraction means;
Voltage rise detection means for detecting that the voltage change component has exceeded a positive first threshold;
A small voltage drop detecting means for detecting that the voltage change component has fallen below a negative second threshold;
A large voltage drop detecting means for detecting that the voltage change component has fallen below a negative third threshold value lower than the second threshold value;
First noise detecting means for detecting that the magnitude of the high-frequency noise included in the voltage change component exceeds a fourth threshold value over a predetermined dead time and a predetermined first time; ,
Second noise detection means for detecting that the magnitude of the high-frequency noise contained in the voltage change component exceeds the fourth threshold value over a predetermined second time;
DC arc generation is detected based on a combination of detection results of the voltage rise detection means, the voltage drop detection means, the voltage drop detection means, the first noise detection means, and the second noise detection means. Determination means for
(A) When the voltage change component is lower than the second threshold and higher than the third threshold, and the magnitude of the high-frequency noise is the dead time and the first When the fourth threshold is exceeded over time, detecting that a series DC arc has occurred on the side where the voltage source is located relative to the DC arc detector;
(B) When the voltage change component becomes a positive value lower than the first threshold, and the magnitude of the high-frequency noise exceeds the fourth threshold over the second time. And detecting that a series DC arc is generated on the side where the load device is located with respect to the DC arc detection device,
(C) When the voltage change component becomes lower than the third threshold, and the magnitude of the high frequency noise exceeds the fourth threshold over the dead time and the first time. A DC arc detection device that detects that a parallel DC arc has occurred. The DC arc detection device further includes current detection means for detecting the presence or absence of current flowing through the cable,
The determination means is
(C1) When the voltage change component becomes lower than the third threshold, and the magnitude of the high frequency noise exceeds the fourth threshold over the dead time and the first time. And when a current is flowing through the positive or negative voltage cable, it is detected that a parallel DC arc has occurred on the side where the load device is located with respect to the DC arc detection device,
(C2) When the voltage change component becomes lower than the third threshold, and the magnitude of the high frequency noise exceeds the fourth threshold over the dead time and the first time. And when no current is flowing through the positive or negative voltage cable, it is detected that a parallel DC arc has occurred on the side where the voltage source having the DC voltage is located with respect to the DC arc detector. The DC arc detection device according to claim 1, wherein: The voltage source and the load device are connected via a circuit breaker,
The determination means is
(D) When the voltage change component alternately exceeds the first threshold value and lower than the third threshold value, and the magnitude of the high frequency noise is the fourth value. When the length of time exceeding the threshold value does not exceed the dead time, the circuit breaker is detected to be closed,
(E) When the voltage change component becomes lower than the third threshold value, the length of time that the magnitude of the high frequency noise exceeds the fourth threshold value is the dead time. The DC arc detection device according to claim 1 or 2, wherein the opening of the circuit breaker is detected when not exceeding.   4. The DC arc detection device according to claim 3, wherein the dead time is longer than a time until the DC arc generated when the circuit breaker is opened and closed is extinguished. The DC arc detector further includes means for amplifying and rectifying the voltage change component,
5. The first and second noise detecting means acquires the magnitude of high-frequency noise contained in the voltage change component from the amplified and rectified voltage change component. The DC arc detection apparatus as described in any one of them.   The first noise detection means detects the magnitude of the high-frequency noise when the magnitude of the high-frequency noise exceeds the fourth threshold value over a continuous or discontinuous fixed time in the first time. 6. The DC arc detection device according to claim 1, wherein the first threshold value exceeds the fourth threshold value over the first time period.   The second noise detection means detects the magnitude of the high-frequency noise when the magnitude of the high-frequency noise exceeds the fourth threshold value over a continuous or discontinuous fixed time in the second time. The DC arc detection device according to any one of claims 1 to 6, wherein it is determined that has exceeded the fourth threshold value over the second time period.   The DC arc detection device according to claim 1, wherein the voltage source is a solar power generation device.

Images