JP2013132157A - Photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect an arc fault in a DC circuit of a photovoltaic power generation system with much noise.SOLUTION: A photovoltaic power generation system includes: a first switch having a first positive terminal and a first negative terminal on an input side, and a second positive terminal and a second negative terminal on an output side; a photovoltaic power generation panel outputting DC power and in which the output is inputted to the first positive terminal and the first negative terminal; a second switch having a third positive terminal and a third negative terminal on an input side, and a fourth positive terminal and a fourth negative terminal on an output side; a positive DC bus line connected to the second positive terminal and the third positive terminal; a negative DC bus line connected to the second negative terminal and the third negative terminal; a power conditioner connected to the fourth positive terminal and the fourth negative terminal and converting DC power outputted from the photovoltaic power generation panel into AC power; and a switch central control device identifying the occurrence place of an arc from voltage differences between the terminals of the same polarity and from voltage differences between the terminals of the opposite polarity.

Description

  The present invention relates to a solar power generation system, and more particularly to detection of arc discharge generated in the solar power generation system.

  Circuit breakers for DC circuit systems generally use a thermal element that protects the circuit from overcurrent using bimetal, and an instantaneous trip element that quickly opens the circuit breaker when a large current flows, such as in a short circuit condition. Is prepared. Recently, in addition to overload and short circuit protection, the importance of DC circuit protection against arc faults has increased. Arc discharge is a high temperature and stable discharge phenomenon. The temperature of surrounding parts rises due to the generation of the arc, and eventually smoke and fire are generated in the cable and terminal block. In particular, in a DC circuit having a circuit voltage of about several hundred volts, the discharge phenomenon is stabilized and there is no current zero point.

  The causes of arc faults can be divided into series arcs and parallel arcs. A series arc occurs in series with the power source and the load. For example, in the bolt connection portion of the wiring, an arc is generated at a location where the bolt is removed due to loose connection. On the other hand, a parallel arc occurs when positive and negative conductors contact each other. A series arc is not detected by an overcurrent protection circuit of a normal circuit breaker because the load current is reduced by the impedance of the arc. The parallel arc can be detected by a thermal element in the case of a small-capacity power source such as photovoltaic power generation, but it takes time to operate because the increase in current is small.

  Patent Document 1 and Patent Document 2 determine the presence or absence of an arc failure using an event in which broadband noise is induced on a cable when an arc occurs on the power cable. The broadband signal is detected using a pickup coil. In order to detect a high frequency component of a signal, it is necessary to increase the sampling frequency of the AD converter and to prevent false alarms due to noise mixing. Even if the presence or absence of an arc fault can be determined, it is not possible to identify the arc fault location, so it is necessary to stop the entire system when a fault is detected.

  Patent Document 3 detects the occurrence of an arc fault by sensing both current drift and voltage drift. Since it is necessary to arrange current and voltage sensors at various locations and to process complicated data, the system becomes expensive.

JP-T-2006-517672 JP 2009-278744 A Japanese Patent No. 3864381

The solar power generation system includes a power conditioner that converts DC power into AC power. From the power conditioner, noise of several kHz level is generated due to high frequency switching by an IGBT (Insulated Gate Bipolar Transistor) or an FET (Field Effect Transistor). This switching noise is normally suppressed to hundreds of tens of kHz or less by the action of the input filter of the power conditioner. In addition, external noise enters the photovoltaic power generation system as the entire system acts as an antenna. An object of the present invention is to accurately detect arc faults (series arc and parallel arc) even in such a noisy DC circuit.

A photovoltaic power generation system according to the present application includes a first switch having a first positive terminal and a first negative terminal on the input side, a second positive terminal and a second negative terminal on the output side, and DC power. A photovoltaic power generation panel that outputs the output to the first positive terminal and the first negative terminal; a third positive terminal and a third negative terminal on the input side; and a fourth positive terminal on the output side And a second switch having a fourth negative terminal, a positive DC bus connected to the second positive terminal and the third positive terminal, and a second negative terminal and a third negative terminal. A power conditioner that is connected to the negative DC bus, the fourth positive terminal and the fourth negative terminal and converts the DC power output by the photovoltaic power generation panel into AC power, the first to fourth positive terminals and the first Captures the voltage applied to the 1st to 4th negative terminals and ends the same polarity The occurrence of an arc and the location of the arc are determined from the voltage difference between the terminals and the voltage difference between the terminals of different polarity, and the first switch and the second switch are opened and closed based on the determined arc occurrence location. And a switch centralized control device for controlling the operation.

  Arc fault detection in a photovoltaic power generation system becomes possible. Moreover, since only a failure location can be selectively separated, a stable and highly reliable photovoltaic power generation system can be supplied.

It is a circuit schematic diagram of a photovoltaic power generation system. It is a figure explaining generation | occurrence | production of a serial arc, and a detection location. It is a graph which illustrates typically the output voltage at the time of series arc generation. It is a figure explaining generation | occurrence | production of a parallel arc, and a detection location. It is a figure explaining the electric current and voltage characteristic of photovoltaic power generation. It is a graph which illustrates typically change of output voltage at the time of parallel arc generation. It is a figure explaining the method of specifying the generation | occurrence | production location of the arc in a solar energy power generation system.

  FIG. 1 is a connection diagram illustrating an example of a solar power generation system 100. The output cables 5p and 5n of the photovoltaic power generation panels 1A to 1C are connected to DC buses 6p and 6n via DC switches 2A to 2C, respectively, which can be remotely operated. The DC switch 2A includes a terminal 21pA and a terminal 21nA on the input side, a terminal 22pA and a terminal 22nA on the output side, and an operation coil 20A through which an operation current flows. Similarly, the DC switch 2B includes a terminal 21pB, a terminal 21nB, a terminal 22pB, a terminal 22nB, and an operation coil 20B. Similarly, the DC switch 2C includes a terminal 21pC, a terminal 21nC, a terminal 22pC, a terminal 22nC, and an operation coil 20C. The DC buses 6p and 6n are connected to the power conditioner 4 through the DC switch 3 having a large rated current. The DC switch 3 includes a terminal 31p, a terminal 31n, a terminal 32p, a terminal 32n, and an operation coil 30. The power conditioner 4 includes a terminal 41p and a terminal 41n. Here, the symbol p represents a positive electrode, and the symbol n represents a negative electrode.

Terminal 21pA, Terminal 21nA, Terminal 22pA, Terminal 22pA, Terminal 21pB, Terminal 21nB, Terminal 22pB, Terminal 22nB, Terminal 21pC, Terminal 21nC, Terminal 22pC, Terminal 22nC, Terminal 31p, Terminal 31n, Terminal 32p, Terminal 32n, Terminal 41p The output of the terminal 41n is input to the switch centralized control device 50 for voltage measurement. The switch centralized control device 50 identifies an arc fault location based on the output of each terminal, and controls the switching of the DC switch corresponding to the identified arc occurrence location via the relay unit 60. When an operating current flows from the relay unit 60 to the operating coils 20A, 20B, 20C, 30, the DC switches 2A, 2B, 2C, 3 are opened. An external command 61 for the DC switches 2 and 3 is introduced into the switch centralized controller 50 from the outside during maintenance. The relay unit 60 may be configured separately from the switch centralized control device 50, and the external command 61 may be directly input to the relay unit 60. When the switch control by the external command 61 is performed, an arc accompanying the switching operation may be generated in the DC switch. Therefore, in order to prevent malfunction, the arc detection function of the switch central control device 50 is masked (fixed) It is desirable to stop for a while).

Next, the operation will be described. Two types of arc faults are considered: series arc and parallel arc. A series arc is when an arc occurs in series with a power source and a load. An arc is generated when the connection part is loosened due to insufficient tightening torque at the bolt connection part, increased contact resistance due to corrosion of the current-carrying part, external vibration, application of tension to the cable, etc. Since the arc has impedance, in the case of a series circuit, the current flowing in the circuit satisfies the following relationship.
Before arc occurrence: I = V / R During arc occurrence: I = (V−Ua) / R
Here, I: load current, V: circuit voltage, R: load resistance, Ua: arc voltage. That is, when an arc is generated, the voltage drops by the arc voltage Ua. Since the load current I decreases due to the occurrence of an arc, it is not detected by a normal overcurrent detection method.

  In the present application, the voltage between terminals of the same polarity adjacent to each other of the DC switches 2 and 3 is monitored, and the occurrence of an arc is captured as an arc voltage. For example, as shown in FIG. 2, it is assumed that a series arc A1 is generated at a connection portion between the terminal 22pB of the DC switch 2B and the terminal 31p of the DC switch 3. FIG. 3 shows a diagram in which the voltage difference between the terminal 22pB and the terminal 31p is taken. The output current of sunlight is about several A to several hundred A. Usually, since the impedance of the output cable 5 is small, the voltage itself shows a small value of mV level. The output of the photovoltaic power generation panel fluctuates due to changes in the amount of solar radiation and is affected by high-frequency switching by a switching element (IGBT or FET) provided inside the power conditioner 4, and thus has a waveform with pulsation (see FIG. 3). The power conditioner 4 detects the output state of the photovoltaic power generation panels 1A to 1C and automatically controls the output to be maximized. Note that the terminal 21pB and the terminal 22pB correspond to adjacent terminals of the same polarity, but the terminal 21pB and the terminal 21pC do not correspond to adjacent terminals of the same polarity because the current does not normally flow.

It is known that the voltage at both ends of the series arc exhibits a value of approximately 10 V or more although it is affected by the metal material, the length of the arc, and the current value. When a DC arc is generated, the voltage difference between the terminal 22pB and the terminal 31p changes rapidly at time t = TA. Since the amount of voltage change (voltage shift) should be 10 V or more, the voltage threshold value Vth1 for determination is generally 5 V to 5
If 0V and the arc is weak, look at 5V to 20V. However, in order to prevent erroneous noise such as lightning and surge voltage from being erroneously determined as a series arc, a time threshold Tth1 is also set for the duration of the voltage difference. Since the duration of the surge voltage is generally several hundred μs or less, a correct judgment can be made if the time threshold Tth1 is expected to be about 1 ms to 10 ms.

With such a determination algorithm, a memory for storing data can be saved. If there is a memory that simply reads the voltage difference signal and stores only the data for the time threshold value Tth1, it can be determined whether or not the voltage difference change over the voltage threshold value Vth1 has continued for a longer time than the time threshold value Tth1. it can. Since it can be determined by the logger data for the window, there is an advantage that the required memory is small, the algorithm is simple, and the detection accuracy is high. Further, since the DC switch group is centrally monitored and controlled, it is possible to eliminate the possibility of erroneous detection of arc generation due to manual operation of the DC switch.

Next, detection of parallel arc generation will be described. Consider the case where a parallel arc B1 occurs between adjacent positive and negative electrodes as shown in FIG. In a commercial AC power source, an arc short circuit between the positive and negative electrodes corresponds to a short circuit between phases. When the power supply capacity is large, such as a commercial AC power supply, a large short-circuit current flows and can be detected by an overcurrent detector. However, the output characteristics of photovoltaic power generation exhibit constant current and constant voltage characteristics as shown in FIG. In solar power generation, even if it becomes a short circuit, a large current does not flow, so it cannot be detected by a thermal (overcurrent) element such as a bimetal, or even if it can be detected, it takes time to detect. Note that the terminal 22pB and the terminal 22nC do not correspond to adjacent terminals of the same polarity because they are not paths through which a normal current flows.

  FIG. 6 is a graph in which the voltage difference between the positive and negative terminals (31p and 31n) of the DC switch 3 in FIG. 4 is monitored. Since it is a positive / negative terminal of different polarity, a solar output voltage of several hundred volts is input between the terminals. If a two-wire short-circuit occurs between the terminals, no current flows to the DC switch 3, and a shortcut is made with the parallel arc B1 to return to the power supply side. Alternatively, a case where the current flows backward and flows into the parallel arc B1 through the DC switch 3 can be considered. In any case, at time t = TB, the voltage suddenly drops and drops from a circuit voltage of about several hundred volts to an arc voltage of about 10 volts. In terms of the sudden drop width, the difference between the circuit voltage and the arc voltage is about several hundred volts.

In terms of a sudden change in the voltage difference, the same method as in the case of the series arc can be adopted as the fault determination algorithm for the parallel arc. That is, the time threshold value Tth2 (1 ms to 10 ms)
) During positive or negative voltage threshold Vth2 (5V-50V, 5V-20 if the arc is weak)
The presence or absence of the parallel arc failure can be determined based on whether or not the voltage difference V) continues to occur.

  By applying the above principle, it is possible to easily know the location where an arc fault has occurred, so only the fault location is separated by a DC switch. In general, when a series arc is detected, the switch on the power supply side in the failure occurrence section (or the load side if there is no such thing) is opened. When a parallel arc is detected, the power supply side and load side switches in the failure occurrence section are opened. For example, in FIG. 7, if an arc failure is detected from the voltage difference between the terminal 21pB and the terminal 21nB and no arc failure is detected from other measurement points, the terminals of the DC switch 2B are connected in parallel in the photovoltaic power generation panel 1B. Arc B2 is generated. If only the DC switch 2B is opened, only the failure area is cut off. A healthy area can be operated continuously. After disconnecting, the fault area is inspected and repaired.

  When an arc failure is detected from the voltage difference between the terminal 22pB and the terminal 31p and no arc failure is detected at the other measurement points, as shown in FIG. 7, there is a gap between the positive electrode circuit of the DC switch 2B and the DC bus 6p. Means that a series arc A2 is generated. If the DC switch 2B is opened, the power supply from the photovoltaic power generation panel 1B is stopped, but the output from other healthy circuits is maintained. It is not necessary to stop all of them, and only the failure area can be inspected and repaired, improving system reliability.

  If an arc fault is detected between the terminal 31p and the terminal 31n, and an arc fault is also detected between the terminal 21pA and the terminal 21nA, between the terminal 21pB and the terminal 21nB, and between the terminal 21pC and the terminal 21nC, the parallel It is estimated that arc B3 has occurred. In this case, it is necessary to open the DC switches 3, 2A, 2B, 2C. Simply opening the internal switch of the power conditioner 4 or the DC switch 3 only protects the load side of the power conditioner 4. Since the sunlight output continues, the failure due to the parallel arc B3 continues without being released. According to the present invention, since an arc failure can be removed, it is possible to prevent an increase in damage due to the arc failure by opening only the failure portion with a switch. Also, since the voltage across the cable with low impedance is monitored, the output (arc voltage) is easy to detect.

  Various locations can be assumed as locations where arcs are generated. In the present application, since a DC switch to be protected is set in advance for each arc occurrence location, any arc fault occurs anywhere and automatically can be detected and opened. The DC switch to be protected is discriminated before and after the DC switch that can open the fault. When the DC switch is operated manually or when the internal switch of the power conditioner 4 is operated, an arc is generated in each switch, so that an erroneous detection is assumed. By centrally monitoring the operation of the power conditioner 4 and the power conditioner 4, it is possible to distinguish arc occurrences accompanying intentional operations. Unnecessary operation due to erroneous detection is eliminated, and the power supply reliability of the entire system can be improved.

  It is preferable that information related to switch control such as a fault location due to an arc or a DC switch open location and control information in the power conditioner are shared between the switch centralized control device 50 and the power conditioner 4. Normally, the power conditioner 4 is automatically controlled so as to obtain the maximum output. Therefore, if the information that one of the photovoltaic power generation panels is opened is transmitted to the control side of the power conditioner 4, the power conditioner 4 The output control function can be maintained.

  The same effect can be obtained by integrating the switch central control device 50 with the control unit of the power conditioner 4. In this case, since the control power supply of the switch centralized control device 50 and the power conditioner 4 can be shared, there is an advantage of downsizing. On the other hand, in order to detect the voltage between the terminals, a large number of detection signals are taken into the switch centralized control device 50. However, it is necessary to insulate or couple the detection signals with high impedance. By applying conventional techniques such as capacitor voltage division, high resistance of several MΩ level, optical coupling, etc., the voltage signal can ensure the necessary insulation performance in the switch centralized control device even when the switch is opened.

  Although the present invention has been described with respect to sunlight output, the same can be said about the series arc fault because the load current decreases even in an AC circuit. In parallel arc faults, if the output of the AC power supply is small (independent private generator that is not linked to commercial power supply), it is still assumed that the fault current will not rise, so the same can be said. The present application can be applied.

  In the present invention, the embodiments can be appropriately modified and omitted within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Solar power generation panel, 2 DC switch, 3 DC switch, 4 Power conditioner, 5 Output cable, 6 DC bus, 50 Switch central control device, 60 Relay part, 100 Solar power generation system

Claims (9)

A first switch having a first positive terminal and a first negative terminal on the input side, and a second positive terminal and a second negative terminal on the output side;
DC power is output, and the output is input to the first positive terminal and the first negative terminal.
A second switch having a third positive terminal and a third negative terminal on the input side, and a fourth positive terminal and a fourth negative terminal on the output side;
A positive DC bus connected to the second positive terminal and the third positive terminal;
A negative DC bus connected to the second negative terminal and the third negative terminal;
A power conditioner that is connected to the fourth positive terminal and the fourth negative terminal, and that converts DC power output from the photovoltaic panel into AC power;
Taking in the voltage applied to the first to fourth positive terminals and the first to fourth negative terminals, the generation of an arc and the generation of an arc from the voltage difference between the terminals of the same polarity and the voltage difference between the terminals of the opposite polarity A photovoltaic power generation system comprising: a switch centralized control device that determines a location and controls a switching operation of the first switch and the second switch based on the determined arc occurrence location.   In the switch centralized control device, a state in which a first voltage threshold and a first time threshold are set in advance and a voltage difference between adjacent terminals of the same polarity has changed more than the first voltage threshold is 2. The photovoltaic power generation system according to claim 1, wherein it is determined that an arc has occurred when the operation is continued for longer than the first time threshold.   3. The switch centralized control device according to claim 2, wherein the first voltage threshold is set in a range of 5 V to 50 V, and the first time threshold is set in a range of 1 ms to 100 ms. Solar power system.   In the switch centralized control device, a second voltage threshold value and a second time threshold value are preset, and a voltage difference between adjacent terminals of different polarities is smaller than the second voltage threshold value. It is discriminate | determined that the arc generate | occur | produced when is continued for longer than the said 2nd time threshold value, The solar power generation system of Claim 1 characterized by the above-mentioned.   5. The switch centralized control device according to claim 4, wherein the second voltage threshold is set in a range of 5 V to 50 V, and the second time threshold is set in a range of 1 ms to 100 ms. Solar power system. 2. The photovoltaic power generation according to claim 1, wherein the switch centralized control device controls an opening / closing operation of the first switch or the second switch based on a command input from the outside. system. The switch centralized control device, when controlling the switching operation of the first switch or the second switch based on an externally input command, stops specifying an arc generation point for a certain period. The solar power generation system according to claim 6.   The photovoltaic power generation system according to claim 1, wherein the power conditioner and the switch centralized control device are integrated. The power conditioner shares the open / closed state of the first switch or the second switch performed in the centralized control device for the switch, and controls the output based on the shared open / closed state. The photovoltaic power generation system according to claim 1.

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