Abnormality detection apparatus and abnormality detection method for power transmission grid of photovoltaic power generation system

Abstract

An abnormality detection apparatus of the present disclosure is for a direct current power transmission unit 30, which transmits direct current power that is outputted from a solar panel 1, and is provided with: sensing circuits 411, 412; a measurement device 401; and an abnormality detection processing unit 402. The sensing circuits are each a two-terminal sensing circuit that includes at least one of a resistor, a capacitor, and an inductor, and that indicates prescribed impedance, and each have one terminal electrically connected to at least one conductor that is for direct current transmission and that is provided in the direct current power transmission unit 30. The measurement device measures the direct current transmission part impedance indicated by the conductor. The abnormality detection processing unit compares the direct current transmission part impedance measured by the measurement device with a determination reference value to detect an abnormality in the direct current power transmission unit.

Description

Abnormality detection device and abnormality detection method for power transmission system of solar power generation system

[0001] The present disclosure relates to an abnormality detection device and an abnormality detection method for a power transmission system of a photovoltaic power generation system, and more particularly to an abnormality detection device and an abnormality detection method for a DC power transmission unit in a photovoltaic power generation system.

[0002] A photovoltaic power generation system typically includes a solar panel containing at least one photovoltaic cell, a junction box, a power conditioner, and grid-connected AC equipment. In many photovoltaic power generation systems, one or more junction boxes correspond to one power conditioner, and each junction box corresponds to one or more solar panels. A current collector box may be installed between the junction box and the power conditioner as needed. In a typical photovoltaic power generation system, DC power from the solar panels is collected through a junction box or current collector box and then sent to the power conditioner. The DC power is converted to AC power in the power conditioner, and finally connected to the grid via grid-connected AC equipment. For this power transmission, the photovoltaic power generation system includes not only an AC power cable for connecting to the grid-connected AC equipment, but also DC power cables and safety equipment such as fuses for transmitting high-current DC power. FIG. 1 is a configuration diagram illustrating an example of a conventional photovoltaic power generation system. The photovoltaic power generation system 90 includes solar panels (solar cells) 1 and 2, a power grid 600, junction boxes 100 and 200, and a power conditioner 300. The solar panel 1 outputs generated DC power to the power conditioner 300 via fuses 101 and 102 and a switch 103 in the junction box 100. Similarly, the solar panel 2 outputs DC power to the power conditioner 300 via fuses 201 and 202 and a switch 203 in the junction box 200. As described above, a typical configuration for a combination of junction boxes and solar panels is that multiple identical units are installed in parallel. The power conditioner 300 generally converts DC power received from multiple junction boxes into AC power and outputs the AC power to the existing power grid 600. The power conditioner 300 typically includes fuses 310 and 311, a DC electromagnetic contactor 320, an inverter unit 330, and an AC electromagnetic contactor 340. The DC electromagnetic contactor 320 opens and closes by electromagnetic means and incorporates a thermal relay, functioning as a DC side switching device. Fuses 310 and 311 are attached to the DC side to protect against overcurrent.The inverter unit 330 converts the input DC power into AC power by alternating the polarity through appropriate switching operations and outputs the AC power. The step-up transformer 500 is provided between the inverter unit 330 and the power grid 600 and transmits power while insulating the inverter unit 330 from the power grid 600. The step-up transformer 500 also boosts the inverter output voltage (up to 500 V) for transmission to the power grid (transmission line, 6.6 kV to 150 kV). The AC electromagnetic contactor 340 is turned on when interconnecting the inverter unit 330 and the power grid 600. The DC electromagnetic contactor 320 is turned on when connecting the solar panel 1 to the power conditioner 300 and functions as a switch. The P-terminal 301 and N-terminal 302 are connected to the P-pole (+) side wiring and the N-pole (-) side wiring aggregated in the connection boxes 100 and 200. That is, DC power passing through the junction boxes 100, 200 is transmitted to the power conditioner 300 via P-side DC cables 150, 250 connected to the P-terminal 301 and N-side DC cables 160, 260 connected to the N-terminal 302. Abnormalities can occur in these components transmitting DC power. Typical abnormalities include cable theft and fuse blowout. Note that while the illustrated solar power generation system 90 is shown with two junction boxes, the number of junction boxes and the number of solar panels in an actual solar power generation system are not particularly limited; for example, the system may be equipped with approximately 10 junction boxes and 10 or 20 solar panels accordingly.

[0003] Most components of a solar power generation system are installed outdoors. For this reason, most metal parts unrelated to power transmission, such as the housing, are electrically grounded. There are three known grounding methods for solar power generation systems: DC grounding, non-grounding, and AC grounding (see Non-Patent Document 1). In all three types of systems, the AC side (the line not shown between the step-up transformer 500 and the power grid 600 in FIG. 1 ) is grounded. In addition, the DC grounding system further includes a circuit for grounding the N-side DC cable 160 (N-side grounding circuit 700 in FIG. 1 ). This circuit electrically grounds the N-side DC cable 160 using a conductor or a low-resistance resistor. For example, in the case of DC grounding, the N-side DC cable 160 is grounded within the power conditioner 300. Note that the P-side DC cable is not generally grounded (P-side grounding). In the case of non-grounding, neither the P-side nor N-side cables are grounded. For this reason, in the non-grounded type, the N-side grounding circuit 700 in FIG. 1 is omitted or is not electrically conductive. The non-grounded type is used when the DC and AC parts are insulated from each other at an appropriate location, such as within the power conditioner 300. In the non-grounded type, the DC part is not substantially grounded. In the AC grounded type, the DC side is not directly grounded. The AC grounded type is used when the DC and AC parts are not insulated from each other. For this reason, in the AC grounded type, the DC part is also grounded by grounding the AC side transformer (step-up transformer 500 in FIG. 1). From an electrical standpoint, the AC grounded type is equivalent to the DC grounded type in which the N-side DC cable is grounded.

[0004] In practical photovoltaic power generation systems, theft of part or all of the DC power cable is a frequent occurrence. Because the DC power cables 150, 160 installed between the junction box and the power conditioner have a large copper wire mass per unit length and are expensive, theft often involves cutting and stealing the cables. In addition to theft, situations often occur in which the fuses 310, 311 that protect the system when excessive current flows through the power cables due to lightning strikes or other causes meltdowns. Furthermore, irregular electrical continuity with the ground, also known as a ground fault or leakage current, can occur. To address these anomalies, there has been a need for a highly reliable and practical method for detecting anomalies in photovoltaic power generation systems, particularly in DC power transmission systems.

[0005] Patent Documents 1 to 3 disclose a configuration for measuring the DC circuit impedance of a DC power supply system (solar panels and DC cables) as a conventional technology for detecting an abnormality in a DC power transmission system of part or all of a solar power generation system. Specifically, paragraphs 0010 to 0011 of Patent Document 1 (JP 2016-131570 A) disclose a configuration in which "an abnormality detection system for a solar power generation facility includes a lower unit that aggregates DC power generated by solar cell units and an upper unit that aggregates the DC power aggregated in the lower unit, in which a plurality of the lower units are connected in parallel to the upper unit, and a measuring instrument that measures impedance is provided on each distribution cable connecting each of the lower units to the upper unit, and a determination unit that detects the abnormality based on the measurement results when the solar cell units are not generating power, and the measuring instrument measures the composite impedance of the solar cell units aggregated in each of the lower units connected in parallel to the upper unit as the impedance." Patent Document 1 discloses that, for the purpose of detecting abnormalities (theft) in solar cell units (solar panels and cables), the solar cell units are configured into lower units and upper units that aggregate the lower units, and that when the solar cell units are not generating electricity, a measuring unit is provided that measures the impedance of the circuit, consisting of solar panels and cables, and a judgment unit is provided that compares the impedance with pre-registered setting values ​​and judges whether the values ​​match, thereby detecting any mismatch as an abnormality.

[0006] Paragraphs 0009-0010 of Patent Document 2 (JP 2017-169263 A) state, "An example of a 'method for detecting theft of a cable connected to a power conditioner' is a method for detecting theft of a cable connected to a power conditioner, which has a solar panel connected to its DC input side via a cable, a power grid connected to its AC output side, and an inverter that converts DC power input from the DC input side into AC power, the method comprising the steps of measuring capacitance between the DC input terminal and a ground terminal of the power conditioner, comparing the measured capacitance value with a disconnection determination value to detect a disconnection in the cable and outputting an abnormality detection signal, and outputting an alarm based on the abnormality detection signal." Patent Document 2 discloses a method for detecting cable theft in a solar power generation system (solar panel, cable, and power conditioner) by measuring the capacitance between the DC input terminal and the ground terminal of the solar panel using a measurement circuit and determining a disconnection from a change in the measured capacitance value. Furthermore, Patent Document 2 also suggests that disconnection may be determined based on insulation resistance instead of capacitance.

[0007] Patent Document 3 (JP 2019-180188 A) also discloses a photovoltaic power generation system including an element called a "grounding device" for a different purpose from those disclosed in Patent Documents 1 and 2. Paragraphs 0006 to 0007 of Patent Document 3 disclose a grounding device that "can be electrically connected to a pair of electric paths that connect a distributed power source including a first electrode and a second electrode and an inverter circuit that converts a DC voltage output from the distributed power source into an AC voltage. The grounding device includes a first terminal electrically connected to at least one of the pair of electric paths, a second terminal electrically connected to ground, and a resistive element electrically connected between the first terminal and the second terminal."

[0008] JP 2016-131470 A JP 2017-169263 A JP 2019-180188 A JP 2013-130536 A

[0009] Takafumi Ishii, "Measures against DC Electrical Accidents in Photovoltaic Power Generation Facilities," Energy & Resources, Vol. 36, No. 6, pp. 369-376 (2015) Kazumi Takano and three others, "Evaluation of Degradation and Failure of Crystalline Silicon Photovoltaic Modules Using Series Resistance (Rs) and Impedance (Z)," AIST Photovoltaic Power Generation Research Results Report 2016, Poster Session, URL: https: / / unit.aist.go.jp / rpd-envene / PV / ja / results / 2016 / poster / P66.pdf Tomio Yamaguchi, Kuniomi Nakamura, "1-3 Relationship between Insulation Resistance Change and Environmental Factors in Outdoor Exposure Tests of Photovoltaic Modules (REAJ 10th Research Presentation)," Journal of Reliability Engineering and Technology, Japan, Vol. 24, No. 4, pp. 333-334 (2002)), DOI: 10.11348 / reajshinrai.24.4_333 Sakurai Y. and K. Kurokawa, "Photovoltaic Power Generation Array Distributed Constant Circuit Simulation - Examination of Simulation Methods," Proceedings of the Joint Research Presentation Meeting of the Japan Solar Energy Society and the Japan Wind Energy Association, No. 2000, pp. 307-310 (November 2000)

[0010] Patent Document 1 discloses measuring the impedance of a circuit consisting of a solar panel and a cable when the solar cell unit is not generating power. Patent Document 2 discloses a conventional technology for detecting theft of a solar power generation system, which measures the resistance R, capacitance C, or impedance between the DC cable and the ground terminal, compares the measured value with a judgment value, and determines and detects the presence or absence of an abnormality. However, in relation to the technology disclosed in Patent Document 1, it has also been reported that the impedance (resistance value) of crystalline silicon solar panels increases as they deteriorate (Non-Patent Document 2). Therefore, in order to accurately detect an abnormality using the technology disclosed in Patent Document 1, it is necessary to deal with fluctuating physical quantities. Furthermore, the disclosure of Patent Document 2 is only applicable to the above-mentioned grounding methods, which are ungrounded or to the P-side DC cable of a DC-grounded N-side type. This is because in DC-grounded N-side types, the N-side DC cable is grounded, making it difficult to measure the impedance of the N-side DC cable between the N-side and the ground.

[0011] It is also known that the insulation resistance and capacitance between the DC cable and the ground constantly fluctuate due to factors such as the large area of ​​a solar panel cluster (solar panel array) and changes in weather conditions (humidity, temperature). For example, Non-Patent Document 3 presents data on the insulation resistance of solar cell modules measured over a nine-year period, showing that the insulation resistance fluctuates significantly, ranging from several hundred kΩ to 1,000 MΩ. Furthermore, Non-Patent Document 4 describes that the junction capacitance of solar cell diodes differs between bright conditions under sunlight and dark conditions at night, affecting the capacitance.

[0012] In addition, Patent Document 3 discloses providing a grounding device (resistance value: up to 10 MΩ) between the DC cable and the ground terminal. However, the purpose and function of the grounding device in this disclosure is to "reduce the voltage to ground at the electrodes of a distributed power source (e.g., solar cell)."

[0013] As described above, conventional devices and methods that measure the impedance of a circuit consisting of a solar panel and a cable, or the impedance between the cable and the ground terminal in the DC portion, and compare it with a judgment value to determine an abnormality do not necessarily provide stable operation, and improvements in practicality are desired. There is an ongoing need for a practical method that can reliably detect abnormalities in the power transmission cable of a solar power generation system, such as theft of the power transmission cable, blowing of a fuse connected to the power transmission cable, ground faults, or leakage currents.

[0014] The present disclosure aims to stably and accurately detect abnormalities in the power transmission cable of a solar power generation system, such as theft of the power transmission cable, blown fuses connected to the power transmission cable, ground faults, or electric leakage. The inventors have created a method for detecting abnormalities in the DC power transmission section of a solar power generation system without adding complex circuit components, and have completed the invention.

[0015] That is, in one embodiment of the present disclosure, there is provided an abnormality detection device for a DC power transmission section that transmits DC power output from at least one solar panel, the abnormality detection device comprising: at least one sensing circuit having two terminals that include at least one of a resistor, a capacitor, and an inductor and exhibits a predetermined impedance, one of the two terminals being electrically connected to at least one of the conductors for DC transmission provided in the DC power transmission section; a measuring device electrically connected to the conductor for measuring the DC transmission section impedance exhibited by the conductor and the sensing circuit; and an abnormality detection processing section that compares the DC transmission section impedance measured by the measuring device with a judgment reference value to detect an abnormality in the DC power transmission section.

[0016] Furthermore, in one embodiment of the present disclosure, there is provided an anomaly detection method for a DC power transmission unit that transmits DC power output from at least one solar panel, wherein the DC power transmission unit is provided with at least one two-terminal sensing circuit that includes at least one of a resistor, a capacitor, and an inductor and exhibits a predetermined impedance, with one of the two terminals electrically connected to at least one of the conductors for DC transmission provided in the DC power transmission unit, and the anomaly detection method includes the steps of measuring the DC transmission unit impedance exhibited by the conductor and the sensing circuit using a measuring device electrically connected to the conductor, and comparing the DC transmission unit impedance with a judgment reference value and generating and outputting an anomaly detection signal indicating an anomaly in the DC transmission system by an anomaly detection processing unit.

[0017] In the present disclosure, impedance is a complex impedance that can be expressed as a complex number, and the value of impedance expressed as a measured value can mean the norm of the complex impedance, i.e., the value obtained by squaring the real and imaginary parts of the complex impedance, adding them together, and taking the square root.

[0018] According to the present disclosure, an abnormality in a DC power transmission unit of a photovoltaic power generation system can be detected with high reliability.

[0019] FIG. 1 is a block diagram showing an example configuration of a conventional solar power generation system. FIG. 2 is a block diagram showing an example solar power generation system to which Examples 1 and 8 of the present disclosure are applied. FIG. 3 is a circuit diagram showing the configuration of an RLC series resonant circuit for a sensing circuit of the present disclosure. FIG. 4 is a graph showing the frequency characteristics of the impedance of an RLC series resonant circuit in a configuration of 10 connection boxes in which the RLC series resonant circuit of the present disclosure is attached to a cable assembly. FIG. 5 is a graph showing the frequency characteristics of the impedance of an RLC series resonant circuit in a configuration of 20 connection boxes in which the RLC series resonant circuit of the present disclosure is attached to a cable assembly (each of the 10 connection boxes is set to a different resonant frequency). FIG. 6 is a block diagram showing an example configuration of a solar power generation system to which Examples 3 and 4 of the present disclosure are applied. FIG. 7 is a circuit diagram showing the configuration of a series circuit of a resistor and a diode for a sensing circuit of the present disclosure. FIG. 8 is a graph showing the voltage-current characteristics of a resistor-diode series circuit of the present disclosure. FIG. 9 is a circuit diagram showing the configuration of an RLC parallel anti-resonant circuit and a series circuit of a diode for a sensing circuit of the present disclosure. FIG. 10 is a graph showing the frequency dependence of impedance in a configuration in which the RLC parallel anti-resonant circuit and a diode series circuit of FIG. 9 are attached to a DC cable. FIG. 11 is a block diagram showing an example of a solar power generation system to which Examples 5, 6, and 7 of the present disclosure are applied. FIG. 12 is a circuit diagram showing the configuration of an RLC parallel anti-resonant circuit for a sensing circuit of the present disclosure. FIG. 13 is a circuit diagram showing the configuration of an RLC series resonant circuit with L in parallel for a sensing circuit of the present disclosure. FIG. 14 is a graph showing the frequency characteristics of circuit impedance in a configuration of 20 connection boxes (each of which is set to a different resonant frequency) in which an RLC series resonant circuit with L in parallel is attached to a cable assembly. FIG. 15 is a circuit diagram showing the configuration of a pure resistor R for a sensing circuit of the present disclosure. FIG. 16 is a block diagram showing an example of a solar power generation system to which Example 9 of the present disclosure is applied. FIG. 17 is a block diagram showing an example of a solar power generation system to which Example 10 of the present disclosure is applied. FIG. 18 is a block diagram illustrating an example of a solar power generation system to which the tenth embodiment of the present disclosure is applied, in which an insulation resistance measuring device is further provided in addition to the solar power generation system of FIG.FIG. 19 is a block diagram illustrating an example of a solar power generation system to which an eleventh embodiment of the present disclosure is applied. FIG. 20 is a block diagram illustrating an example of a solar power generation system to which a twelfth embodiment of the present disclosure is applied. FIG. 21 is a block diagram illustrating an example of a solar power generation system to which a thirteenth embodiment of the present disclosure is applied. FIG. 22 is a block diagram illustrating an example of a solar power generation system to which a fourteenth embodiment of the present disclosure is applied. FIG. 23 is a block diagram illustrating an example of a solar power generation system to which a fifteenth embodiment of the present disclosure is applied. FIG. 24 is a block diagram illustrating an example of a solar power generation system to which a sixteenth embodiment of the present disclosure is applied. FIG. 25 is a block diagram illustrating an example of a solar power generation system to which a seventeenth embodiment of the present disclosure is applied. FIG. 26 is a block diagram illustrating an example of a solar power generation system to which an eighteenth embodiment of the present disclosure is applied.

[0020] Hereinafter, embodiments of the present disclosure will be described. In the following description, unless otherwise specified, common parts or elements are designated by common reference numerals throughout the drawings. Furthermore, in the drawings, elements of each embodiment are not necessarily shown in proportion to each other. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0021] 1. Overview An abnormality detection device and an abnormality detection method according to an embodiment of the present disclosure will be described in comparison with a conventional N-side grounded configuration (photovoltaic power generation system 90, FIG. 1).

[0022] The anomaly detection device of this embodiment is simply configured by adding a circuit for detecting anomalies (hereinafter, "sensing circuit") and an anomaly detection processing unit to the conventional solar power generation system 90 illustrated in FIG. 1 , and the anomaly detection method of this embodiment can be implemented as the operation of such a solar power generation system. The sensing circuit is typically electrically connected between a DC input terminal and a ground terminal for a DC cable connecting a junction box and a power conditioner. Because the DC cable is connected to the DC input terminal, the sensing circuit can also respond to blown DC cables and fuses connected thereto, ground faults, or ground faults. For this purpose, the sensing circuit is generally a two-terminal circuit block that includes at least one of a resistor, a capacitor, and an inductor to exhibit a predetermined impedance. A preferred sensing circuit may further include a diode.

[0023] The specific configuration and operation of the anomaly detection device and anomaly detection method of this embodiment will be described below with reference to examples. The content described in each example can be applied to any of the anomaly detection devices and anomaly detection methods of this embodiment as long as there is no contradiction. In the following examples, a solar power generation system is described in which one junction box is provided for each solar panel, and two junction boxes are used in each solar power generation system. However, the number of solar panels per junction box and the number of junction boxes per solar power generation system are not particularly limited. Furthermore, in the description of each solar power generation system, the description of the solar panel 1 and the junction box 100 connected thereto also applies to the solar panel 2 connected in parallel and the junction box 200 connected thereto.

[0024] 2. Example 1 2-1. Overall Configuration FIG. 2 shows the configuration of a solar power generation system 12 to which Examples 1 and 8 of the anomaly detection device and anomaly detection method of the present embodiment are applied. In the present disclosure, the DC power transmission unit of the solar power generation system refers to the portion that transmits DC power generated between the solar panels 1 and 2 and the power conditioner 300. This DC power transmission unit is the target for detecting anomalies in the anomaly detection device and anomaly detection method of the present disclosure. Using the solar power generation system 12 shown in FIG. 2 as an example, the DC power transmission unit 30 is mainly composed of P-side DC cables 150 and 250, N-side DC cables 160 and 260, and fuses 310 and 311. Typical anomalies in the DC power transmission unit 30 include disconnection of the P-side DC cables 150 and 250 and the N-side DC cables 160 and 260 (including disconnection caused by theft or other human error), meltdown of the fuses 310 and 311, a ground fault, or a ground fault. In order to reliably detect such an abnormality in the DC power transmission unit 30, the photovoltaic power generation system 12 ( FIG. 2 ) of Example 1 of this embodiment includes detection circuits 411, 412, 421, and 422 between the ground and appropriate positions of the DC power transmission unit 30 in the photovoltaic power generation system 12. The appropriate positions are positions where an abnormality in the DC power transmission unit 30 or a portion thereof can be detected through an electrical connection, and the physical location is not particularly limited. The appropriate positions are typically within or near the junction boxes 100 and 200. For example, the DC power transmission unit 30 includes cable assemblies 35 and 36 transmitting DC power on the positive and negative poles. Corresponding to the junction boxes 100 and 200, the cable assembly 35 includes a P-side DC cable 150 and a P-side DC cable 250, and the cable assembly 36 includes an N-side DC cable 160 and an N-side DC cable 260, respectively. The cable assemblies 35 and 36 may be an integrated cable, or may refer to a collection of cables that are electrically connected in use directly or via fuses, etc. In this configuration, sensing circuits 411, 412, 421, 422 are added between the P-side DC cable 150, the N-side DC cable 160, the P-side DC cable 250, and the N-side DC cable 260, respectively, and the ground.In FIG. 2 , the sensing circuits 411, 412 are connected to the P-side and N-side DC cables 150, 160 between the switch 103 and the power conditioner 300. However, the anomaly detection device and method of this embodiment are not limited to these locations. The sensing circuits 411, 412 can be installed anywhere within the connection box 100 or near the solar panel 1. In the anomaly detection device and method of this embodiment, the sensing circuits 411, 412 are installed at any location within a range from the power conditioner 300 as the starting point to any position up to the solar panel 1 as the end point, where an abnormality should be detected. However, it is not necessary to connect sensing circuits to all power cables. In this embodiment, the impedance of each of the cable assemblies 35 and 36 of the DC power transmission unit 30 is measured, including the characteristics of the sensing circuits. This measurement is performed by the monitoring processing unit 400. The measured impedance is compared with a reference value (criterion value) to detect an abnormality in the DC power transmission unit 30 .

[0025] The specific configuration of the solar power generation system 12 of Example 1 will be described in comparison with the solar power generation system 90 of FIG. 1 . P-side DC cables 150 and 250 form a P-side cable assembly 35 that connects the P-side output of each of the junction boxes 100 and 200 to a DC input terminal (P terminal) 301. Similarly, N-side DC cables 160 and 260 form an N-side cable assembly 36 that connects the N-side output of each of the junction boxes 100 and 200 to a DC input terminal (N terminal) 302. The solar panel 1 may be a group of at least one solar panel. The junction box 100 is used to collectively transmit DC power from at least one solar panel in the group, depending on practical convenience such as ease of facility management. The P-side cable assembly 35 and the N-side cable assembly 36 are branched on one side according to the number of junction boxes 100 and 200 for the solar panels 1 and 2, and the other side is connected to the power conditioner 300. Typically, the power conditioner 300 has one fuse 310, 311 connected to each connection box. In addition to this typical configuration, various electrical connection configurations for the DC power transmission unit 30 can be adopted depending on the management purpose and power capacity. As an additional component compared to the solar power generation system 90, within the connection box 100, sensing circuits 411, 412 are attached to the P-side DC cable 150 and the N-side DC power cable 160. The sensing circuits 411, 412 are generally two-terminal circuit elements or combination circuit blocks, with one of the two terminals connected to the P-side DC cable 150 and the N-side DC power cable 160 and the other terminal grounded. The sensing circuits 411, 412 are configured to detect abnormalities in the DC power transmission unit 30. Specifically, they include resistors, capacitors, and inductors and exhibit a specific impedance. In a preferred configuration, the sensing circuits 411, 412 may further include diodes.

[0026] The power conditioner 300 employed in the solar power generation system 12 includes a monitoring processing unit 400 as an additional component compared to the solar power generation system 90. The monitoring processing unit 400 includes an impedance measurement circuit 401, an abnormality detection processing unit 402 for detecting abnormalities such as cable theft and ground faults, and an alarm output circuit 403.

[0027] Specifically, the impedance measurement circuit 401 is connected between the P terminal 301 or N terminal 302, which is a DC input terminal of the power conditioner 300, and the ground terminal 303, and measures the impedance (DC transmission section impedance) Zpm between the P terminal 301 and the ground terminal 303 and the impedance (DC transmission section impedance) Znm between the N terminal 302 and the ground terminal 303, and outputs the measured values ​​to the abnormality detection processing unit 402. The impedance is measured by applying either a DC voltage or an AC voltage, or both, between the P terminal 301 or N terminal 302 and the ground terminal 303, measuring the voltage and current, and then determining the impedance from the measured voltage and current.

[0028] The abnormality detection processing unit 402 compares the impedances Zpm and Znm measured by the impedance measurement circuit 401 with a separately set impedance reference value Zs, and outputs a cable abnormality detection signal. The abnormality detection processing unit 402 stores the preset impedance reference value Zs in an appropriate recording unit.

[0029] The alarm output circuit 403 outputs an alarm output to an alarm output terminal 404 based on the abnormality detection signal input from the abnormality detection processing unit 402. An alarm means (not shown) such as a display means or an alarm means is connected to the alarm output terminal 404, and when an alarm output is output from the alarm output terminal 404, it is possible to notify of an abnormality. The alarm means may be provided within the power conditioner 300.

[0030] 2-2. Operation An example of anomaly detection operation is described below. The example illustrates an anomaly detection operation performed to detect cable cuts due to DC cable theft. A similar operation can be applied to fuse blowouts, which exhibit similar electrical behavior to cable cuts. First, a method for setting the impedance Ze of the detection circuits 411, 412, which combine resistors, capacitors, inductors, diodes, and other necessary electronic components, is described. Assume that a solar power generation system with a configuration similar to that of the solar power generation system 12 shown in FIG. 2 has 10 junction boxes, each arranged in parallel. In this case, a total of 10 detection circuits 411, 421, ..., each indicating an impedance Ze, are connected in parallel to each other in the cable assembly 35 consisting of the P-side DC cables 150, 250, .... In this configuration, under normal conditions, the impedance Zpm of this parallel circuit measured by the impedance measurement circuit 401 is Ze / 10. In this state, if, for example, one of the P-side DC cables 150, 250, ... of the cable assembly 35 is first cut, the number of parallel connections changes from 10 to 9. In response to this, the impedance value Zpm exhibited by the cable assembly 35 of the DC cables changes to Ze / 9.

[0031] It is desirable that an alarm be issued immediately when at least one of the P-side or N-side DC cables is disconnected in any one of the junction boxes among the DC power transmission unit 30 including the P-side DC cables and the N-side DC cables wired to the 10 junction boxes. Therefore, the impedance reference value Zs is set to a value that satisfies Ze / 10<Zs<Ze / 9 (1).

[0032] When the number of cut cables in the cable assembly 35 consisting of the P-side DC cables 150, 250, ... increases sequentially from one to two, the impedance Zpm changes as follows: Before cable cut: Zpm = Ze / 10 < Zs (2) After one cable cut: Zpm = Ze / 9 > Zs (3) After two cables cut: Zpm = Ze / 8 > Zs (4) Therefore, by setting the impedance reference value Zs according to equation (1), the abnormality detection processing unit 402 immediately outputs an abnormality detection signal when the first cable is cut, and the alarm output circuit 403 subsequently outputs an alarm to the alarm output terminal 404 based on the abnormality detection signal input from the abnormality detection processing unit 402. By activating some kind of suppression device in response, damage can be minimized. This suppression device may include, for example, an alarm sound device, an alarm light device, or a remote alarm communication device. Even if a second, third, etc. cable is cut after the first, the measured impedance Zpm of the cable assembly 35 will always be greater than the impedance reference value Zs, and an alarm will continue to be output. The above-described operation applies to the cable assembly 35 including the P-side DC cable. However, if the sensing circuits 412, 422, etc., each representing an impedance Ze, are connected in parallel to the cable assembly 36 including the N-side DC cables 160, 260, etc., the same operation can be performed for the impedance Znm, which is the DC transmission section impedance of the cable assembly 36 for the N-side DC cable. Therefore, if the first cable cut is the N-side DC cable, Znm will change in the same way, and a similar detection and alarm output operation can be performed. The solar panels 1 and 2 and the inverter unit 330 in FIG. 2 are insulated from the ground, and only the sensing circuit is electrically connected to the ground. Therefore, abnormality detection can be performed regardless of whether the switches 102, 203 or the DC electromagnetic contactor 320 are in an open or closed state, i.e., regardless of whether power from the solar panel is being transmitted or not.

[0033] In the above-mentioned deterrent device, the warning sound generating device can emit sounds at an appropriate volume, such as a machine-generated sound such as a siren or an announcement voice with a warning message that can be understood by the alarm recipient. The warning light emitting device can emit any light useful for observing the situation or intimidating the alarm recipient, such as a light that illuminates the surroundings, a flickering colored light, or a flashing light. The remote alarm communication device is a communication transmitter, and can send a message or signal to, for example, a security company's monitoring center to report an abnormality. For this purpose, there are no particular restrictions on the communication network used by the remote alarm communication device. In addition to always-on networks and closed networks, any communication network or communication path can be used, such as any public access network including LTE (Long Term Evolution) lines and 5G (fifth generation mobile communication system) lines, or satellite lines.

[0034] 2-3. Sensing Circuit The configuration of the sensing circuit of the solar power generation system 12 in Example 1 will be described in detail. FIG. 3 is a circuit diagram of an RLC series resonant circuit for the sensing circuits 411, 412, 421, and 422 of the present disclosure shown in FIG. 2. In the solar power generation system 12, the sensing circuits 411, 412, 421, and 422 may be, for example, an RLC resonant circuit (RLC series resonant circuit) 1000 or a series circuit (not shown) of the RLC series resonant circuit 1000 and a diode. The solar power generation system 12 of Example 1 employing the RLC series resonant circuit 1000 can achieve the following unique effects. First, because the capacitor C is arranged in series in the RLC series resonant circuit 1000, DC insulation is provided between the two terminals of the sensing circuit. Therefore, the RLC series resonant circuit 1000 can be directly applied to ungrounded and AC-grounded solar power generation systems. Second, the RLC series resonant circuit 1000 can be used to detect abnormalities in the cable assembly 35, which is composed of the positive-side DC cables 150, 250, etc., in a DC-grounded configuration. In this case, the sensing circuits 411 and 421 are installed, but the sensing circuits 412 and 422 are not, as shown in FIG. 2 . Third, because the RLC series resonant circuit 1000 has the frequency characteristics of a resonant circuit, it can more accurately detect impedance changes caused by phenomena such as cable breakage than sensing circuits that use resistors (pure resistance) that do not exhibit frequency characteristics. FIG. 4 is a graph showing the frequency characteristics of impedance in a configuration of 10 connection boxes with sensing circuits attached to the cable assemblies 35 and 36. The frequency characteristics shown here are for a resonant frequency of 1000 kHz, R of 100 kΩ, L of 3 mH, and C of 8.44 pF. In this configuration, a total of 10 connection boxes each have a sensing circuit attached to each of the P-side DC cables 150, 250, ... that make up the P-side cable assembly 35, and similarly, one is attached to each of the N-side DC cables 160, 260, ... that make up the N-side cable assembly 36. The sensing circuits in each cable assembly are electrically connected in parallel. The solid line shows the frequency characteristics when all of the parallel DC cables are healthy, and the dashed line shows the frequency characteristics when the first DC cable is cut, reducing the number of parallel cables to nine.That is, when the first one of the P-side DC cable or the N-side DC cable is cut, the impedance changes from Ze / 10 (solid line) to Ze / 9 (dashed line).

[0035] The measured values ​​of the DC transmission unit impedance, Zpm and Znm, can be measured by applying an AC voltage (sine wave, square wave, etc.) at the resonant frequency to the sensing circuit, measuring the current value at the same frequency, and performing signal processing such as dividing the voltage value by the current value. The DC transmission unit impedance measured with an AC voltage (sine wave, square wave, etc.) near the resonant frequency is minimized at the resonant frequency and does not change significantly with small frequency shifts. Therefore, the DC transmission unit impedance can be measured stably and with high accuracy using a narrow-band frequency filter. Furthermore, since the impedance is small near the resonant frequency, the measurement signal (i.e., the measured current value) becomes larger, increasing the SNR (signal-to-noise ratio), enabling even more accurate sensing. Additionally, by measuring only the current value signal that has a constant phase difference from the applied voltage using a phase detection method or the like, noise can be further removed, enabling more accurate measurements. This solves the problem addressed by this disclosure.

[0036] 4. Example 2 In Example 1, FIG. 2 illustrates a configuration in which ten junction boxes each have one sensing circuit attached to the positive and negative DC cables. If the number of junction boxes is further increased to, say, 20, the change in resistance when one positive DC cable is disconnected would be from Zpm / 20 to Zpm / 19, a change rate of 5%, half that of Example 1. Therefore, increasing the number of junction boxes requires higher accuracy in resistance measurement. Therefore, in Example 2 of this embodiment, an RLC series resonant circuit 1000 with a different resonant frequency can be attached to every ten junction boxes. FIG. 5 is a graph showing the impedance-frequency characteristics of a configuration including ten junction boxes each having a sensing circuit with a first resonant frequency attached to cable assemblies 35 and 36 and ten junction boxes each having a sensing circuit with a second resonant frequency attached to cable assemblies 35 and 36. Here, the frequency characteristics are shown for a configuration in which R is 5 kΩ, L is 5 mH, and C is 56.3 pF to set the first resonant frequency to 300 kHz, and R is 5 kΩ, L is 5 mH, and C is 6.25 pF to set the second resonant frequency to 900 kHz. In this configuration, the P-side DC cables 150, 250, etc. that make up the P-side cable assembly 35 are connected to the same number of junction boxes, i.e., a total of 20 sensing circuits 411, 421, etc. Similarly, the N-side DC cables 160, 260, etc. that make up the N-side cable assembly 36 are connected to the same number of junction boxes, i.e., a total of 20 sensing circuits 412, 422, etc., for a total of 40 sensing circuits. The sensing circuits in each cable assembly are electrically connected in parallel. The solid curve in Figure 5 represents the frequency characteristics when all 20 parallel P (or N) side DC cables are healthy, and the dashed curve represents the frequency characteristics when the first DC cable in a junction box equipped with a detection circuit with a resonant frequency of 900 kHz is cut, bringing the total number of parallel cables to 19. Since a different resonant frequency is set for each of the 10 junction boxes, when the first of either the P-side DC cable or the N-side DC cable is cut, the impedance near the resonant frequency changes from Ze / 10 (solid line) to Ze / 9 (dashed line), with a rate of change of 9%, which is roughly the same as in Example 1.In this way, especially when the number of sensing circuits is large, by installing sensing circuits with different resonant frequencies for every certain number of connection boxes, it is possible to prevent the rate of change of the resistance value from becoming small, that is, to prevent the denominator of equation (1) from becoming large.

[0037] 4. Example 3 Example 3 is a configuration of an anomaly detection device employing a sensing circuit consisting of a series circuit of a pure resistor and a diode in this embodiment, and is applied to the solar power generation system 14 shown in FIG. 6 . The circuit diagram in FIG. 7 shows a series circuit 1010 of a resistor and a diode (resistance-diode series circuit), which is a typical configuration for the sensing circuit of Example 3. As shown in FIG. 6 , in the solar power generation system 14, sensing circuits 413 and 423 are attached to the P-side DC cables 150 and 250 that form the cable assembly 35, and sensing circuits 414 and 424 are attached to the N-side DC cables 160 and 260 that form the cable assembly 36. The sensing circuits 413, 414, 423, and 424, including the diodes shown in FIG. 6 , have the configuration of the resistance-diode series circuit 1010 ( FIG. 7 ). The orientation of the diodes is as shown in FIG. 6 . FIG. 8 shows the voltage-current characteristics of the resistance-diode series circuit 1010 alone. As shown in FIG. 6 , the P-side and N-side DC cables 150 and 160 are equipped with diodes in opposite directions. The P-side and N-side DC cables 150 and 160 are connected to the positive and negative poles of the solar panel 1, respectively. Therefore, if the P-side potential is positive and the N-side potential is negative relative to the ground during power generation, the diodes in the sensing circuits 413 and 414 are reverse-biased. This prevents current from flowing from the P-side cable assembly 35 to the ground, even if a ground fault (short circuit with the ground) occurs in the N-side cable assembly 36. Similarly, if a ground fault occurs in the P-side cable assembly 35, current from the ground does not flow into the N-side cable assembly 36.

[0038] Continuing to denote the impedance of each sensing circuit as Ze, the sensing circuit impedance Ze and the impedance reference value Zs for detecting an abnormality can be set in the same manner as in Example 1 (photovoltaic power generation system 12), and the operation of detecting an abnormality in the DC power transmission unit 30 can also be performed in the same manner as in Example 1 (photovoltaic power generation system 12). The DC transmission unit impedances Zpm and Znm can be measured by applying an AC voltage to the sensing circuit, measuring the current when a forward voltage is applied, and performing signal processing such as dividing the current by the voltage, taking into account diode characteristics. Note that, as in Example 1, in this example, abnormality detection can be performed regardless of whether or not solar panel power is being transmitted. To detect an abnormality during power transmission, it is useful to, for example, significantly deviate the resonant frequency of the sensing circuit from the frequency of the inverter unit 330, which may be a noise source, i.e., the PWM (Pulse Width Modulation) modulation frequency that performs DC / AC conversion. The PWM modulation frequency is typically at most about 10 kHz.

[0039] In Example 3, the sensing circuit has diode characteristics, which can provide the following unique effects. First, since diodes are connected in series in the sensing circuit for both the P-side cable assembly 35 and the N-side cable assembly 36, they are polarity-insulated from the ground. In other words, Example 3 can be applied to an ungrounded solar power generation system. Second, Example 3 cannot be applied to the N-side DC cable in a DC-grounded system, but it can detect abnormalities in the P-side cable assembly 35. In this case, only the sensing circuit 413 is installed.

[0040] 5. Example 4 Example 4 is an anomaly detection device employing a sensing circuit comprising an RLC parallel anti-resonant circuit and a series circuit of diodes in this embodiment. As with Example 3, Example 4 is implemented in the solar power generation system 14 configuration shown in FIG. 6 . FIG. 9 shows a circuit diagram of a sensing circuit 1020 (RLC parallel anti-resonant diode series circuit) employing an RLC parallel anti-resonant circuit and a series circuit of diodes employed in Example 4. In the solar power generation system 14, sensing circuits 413 and 423 are attached to a cable assembly 35 consisting of P-side DC cables 150, 250, etc., and sensing circuits 414 and 424 are attached to a cable assembly 36 consisting of N-side DC cables 160, 260, etc., with the sensing circuits 413 and 414 having the configuration of the RLC parallel anti-resonant diode series circuit 1020 ( FIG. 9 ). The orientation of the diodes in the sensing circuits 423 and 424 is reversed, and the orientation of the diodes in each sensing circuit is as shown in FIG. 6 . FIG. 10 shows the frequency dependence of the DC transmission impedance in a solar power generation system 14 including ten junction boxes, each of which has an RLC parallel anti-resonant diode series circuit 1020 (R = 100 kΩ, L = 4 mH, C = 6.33 pF) attached to the DC cables 150 and 250 constituting the P-side cable assembly 35 and the DC cables 160 and 260 constituting the N-side cable assembly 36. In this configuration, ten sensing circuits are attached in parallel to each of the P-side cable assembly 35 and the N-side cable assembly 36. The solid line shows the frequency characteristics when the ten parallel DC cables are healthy, and the dashed line shows the frequency characteristics when the first DC cable is cut, reducing the number of parallel cables to nine. In other words, when the first DC cable in either the P-side or N-side DC cable is cut, the impedance changes from Ze / 10 (solid line) to Ze / 9 (dashed line). The impedances Zpm and Znm, which are the DC transmission part impedances, can be measured by applying an AC voltage (sine wave, square wave, etc.) at an anti-resonance frequency to the sensing circuit, measuring the current value at the same frequency (or a multiplied frequency) taking into account the diode characteristics, and performing signal processing such as dividing the voltage value by the current value. When the impedance is measured with an AC voltage (sine wave, square wave, etc.), it reaches a maximum at the anti-resonance frequency, so the impedance does not change with slight deviations in frequency.For this reason, noise can be removed using a narrowband frequency filter, etc., allowing for stable and accurate impedance measurements. Also, because the diode is installed in series, current flows only during the forward half-wave of the applied AC voltage. The current contains frequency components (or multiplied frequency components) of the anti-resonance frequency, so impedance can be measured from this value. Furthermore, if measurements are limited to only currents with a certain phase difference from the applied voltage, noise can be removed, allowing for accurate measurements.

[0041] Thus, by employing the RLC parallel anti-resonant diode series circuit 1020 as the sensing circuit in Example 4, the following unique effects can be achieved. First, because both the cable assembly 35 consisting of the P-side DC cables 150, 250, ... and the cable assembly 36 consisting of the N-side DC cables 160, 260, ... have diodes inserted in series between them and ground, providing polarity insulation, Example 4 can be applied to an ungrounded solar power generation system. Second, Example 4 can also be applied to detecting an abnormality in the P-side DC cable 150 in a DC-grounded system. In this case, only the sensing circuit 413 is installed. Third, because the RLC parallel anti-resonant circuit exhibits the frequency characteristics of an anti-resonant circuit ( FIG. 10 ), measurements near the anti-resonant frequency can accurately detect changes in the DC transmission section impedance (i.e., cable breakage). Note that Example 4 uses a series circuit consisting of an RLC parallel anti-resonant circuit and a diode, but a series circuit consisting of an RLC series resonant circuit and a diode can also achieve similar effects. In this case, the frequency characteristics will be similar to those shown in FIG. 4, and the same effects as those in the first and second embodiments can be expected.

[0042] 6. Example 5 Example 5 is an anomaly detection device and an anomaly detection method that employ a sensing circuit composed of an RLC parallel anti-resonant circuit in this embodiment, and is applied to the configuration of the solar power generation system 16 shown in FIG. 11 . In the solar power generation system 16, sensing circuits 412 and 422 are attached to the DC cables 160 and 260 that constitute the cable assembly 36 on the N-pole side. FIG. 12 shows a circuit diagram of an RLC parallel anti-resonant circuit 1030 employed for the sensing circuit 422 in Example 5. The solar power generation system 16 employing the anomaly detection device and anomaly detection method of Example 5 can achieve the following unique effects. First, because the RLC parallel anti-resonant circuit has an insulator attached in parallel, the cable assembly 36 on the N-pole side is DC-short-circuited to the ground via the insulators in the sensing circuits 412 and 422. This makes it possible to detect an anomaly in the N-side DC cable in a DC-grounded system with conductor grounding, which was previously not possible. Second, as in the fourth embodiment, the use of an RLC parallel anti-resonant circuit enables accurate detection of changes in the DC transmission section impedance (i.e., cable breakage) near the anti-resonance frequency. The impedance measurement method is the same as in the fourth embodiment. Unlike the RLC parallel anti-resonant diode series circuit 1020 ( FIG. 9 ), the RLC parallel anti-resonant circuit 1030 of the fifth embodiment does not include a diode, enabling full-wave measurements. Furthermore, simply employing the RLC parallel anti-resonant circuit 1030 for the fifth embodiment in the sensing circuits 412 and 422 does not enable detection of abnormalities in the P-side DC cable. However, by combining the first to third embodiments and employing the sensing circuits (the RLC series resonant circuit 1000, the resistive diode series circuit 1010, and the RLC parallel anti-resonant diode series circuit 1020) or the pure resistive circuit 1050 (described below) as the sensing circuits for the DC cables 150 and 250 that constitute the P-side cable assembly 35, it becomes possible to detect abnormalities in the P-side cable assembly 35.

[0043] 7. Example 6 Example 6 is an anomaly detection device and an anomaly detection method that employs a detection circuit formed of an RLC series resonant circuit in this embodiment, and is applied to the configuration of the solar power generation system 16 shown in FIG. 11 . FIG. 13 shows a circuit diagram of an RLC series resonant circuit 1040 in which L is connected in parallel, which is employed for the detection circuits 412 and 422 in Example 6. The solar power generation system 16 employing the anomaly detection device and anomaly detection method of Example 6 can achieve the following unique effects. First, because inductors L1 and L2 are connected in parallel with each other, an anomaly in the N-side DC cable can be detected in a DC-grounded system with conductor grounding, as in Example 5. Second, as in Example 2, by employing multiple resonant frequencies, anomalies can be detected with particularly high accuracy when a large number of connection boxes are used. 14 is a graph showing the frequency characteristics of impedance in a configuration including ten junction boxes with sensing circuits for the first resonant frequency attached to cable assemblies 35 and 36, and ten junction boxes with sensing circuits for the second resonant frequency attached to cable assemblies 35 and 36. The graph shows the frequency characteristics when R is set to 5 kΩ, L1 is set to 17 mH, L2 is set to 5 mH, and C is set to 56.3 pF to set the first resonant frequency to 300 kHz, and R is set to 5 kΩ, L1 is set to 17 mH, L2 is set to 5 mH, and C is set to 6.25 pF to set the second resonant frequency to 900 kHz. In this configuration, the N-side DC cables 160, 260, etc. that make up the N-side cable assembly 36 are each connected to the same number of junction boxes, i.e., 20 sensing circuits 412, 422, etc. No sensing circuit is connected to the P-side cable assembly 35, resulting in a total of 20 sensing circuits. The sensing circuits in each cable assembly are electrically connected in parallel. The solid line shows the frequency characteristics when all 20 parallel N-side DC cables are in a healthy state, and the dashed line shows the frequency characteristics when the first DC cable of the connection box equipped with a sensing circuit with a resonant frequency of 900 kHz is cut, bringing the total number of parallel cables to 19.Since a different resonant frequency is set for every 10 connection boxes, when the first of any one of the N-side DC cables is cut, the impedance near the resonant frequency changes from Ze / 10 (solid line) to Ze / 9 (dashed line), and the rate of change is 9%, i.e., roughly the same value as in Example 1. In this way, particularly when the number of sensing circuits is large, by attaching sensing circuits with different resonant frequencies to a certain number of connection boxes, it is possible to prevent the rate of change of the resistance value from becoming small (preventing the denominator of Equation (1) from becoming large).

[0044] 8. Example 7 Example 7 is an anomaly detection device and an anomaly detection method that employ a sensing circuit consisting of a pure resistor R in a DC-grounded photovoltaic power generation system that is grounded through high resistance, as in the present embodiment. As with Examples 5 and 6, Example 7 is implemented in the configuration of the photovoltaic power generation system 16 shown in FIG. 11 . That is, in the photovoltaic power generation system 16, sensing circuits 412 and 422 are attached to the DC cables 160 and 260 that constitute the N-pole cable assembly 36. FIG. 15 is a circuit diagram of a pure resistance circuit 1050 that employs a sensing circuit 1050 consisting of a pure resistor R employed for the sensing circuit of Example 7. The photovoltaic power generation system 16 of Example 7, which employs a sensing circuit 1050 consisting of a pure resistor, can achieve the following unique effects. Because the sensing circuit is a pure resistor, it can be applied to a DC-grounded system that is grounded through high resistance, and the high resistance of the sensing circuit can be shared with the high resistance of the ground. Note that simply employing the sensing circuit 1050 of Example 7 as the sensing circuits 412 and 422 does not enable an anomaly in the P-side DC cable to be detected. However, by combining the embodiments so that the sensing circuits of Examples 1 to 3 (RLC series resonant circuit 1000, resistive diode series circuit 1010, RLC parallel anti-resonant diode series circuit 1020) are connected to the DC cables 150 and 250 that form the cable assembly 35 on the P-pole side, it becomes possible to sense abnormalities in the cable assembly 35 on the P-pole side.

[0045] 9. Example 8 Example 8 is implemented using the same configuration as Example 1 for the solar power generation system 12 shown in FIG. 2 , with the addition of a sensing circuit 1050 ( FIG. 15 ) consisting of pure resistance R as the sensing circuits 411, 412, 421, and 422. In Example 8, the sensing circuits 411, 412, 421, and 422 are attached to the positive-side DC cables 150 and 250 and the negative-side DC cables 160 and 260. Therefore, focusing on the solar panel 1, a closed circuit is formed that traces the positive terminal of the solar panel 1, the positive-side DC cable 150, the sensing circuit 411, the ground wire, the negative-side DC cable 160, and the negative terminal of the solar panel 1 in this order. The same applies to the solar panel 2. In this case, if the sensing circuit is a pure resistance, a DC current will always flow through this closed circuit. However, if the impedance Ze (i.e., the resistance value Re) is sufficiently large, for example, 500 kΩ, the closed circuit current can be sufficiently small even when the solar panel output voltage is approximately 1000 V, resulting in no practical problems. In fact, when this numerical example is applied to a configuration with 10 junction boxes, the closed circuit current is 1000 V / (2 × 500 kΩ × 10) = 0.1 A. Example 8 can achieve the following unique effects. First, by sufficiently increasing the resistance value of the pure resistor R, both the positive-side cable assembly 35 and the negative-side cable assembly 36 are grounded with high resistance, which is essentially equivalent to being insulated, making it applicable to ungrounded solar power generation systems. Second, because the sensing circuit is a pure resistor, it can be applied to DC-grounded systems that are grounded with high resistance, and the high resistance of the grounding resistor and the sensing circuit can be shared. In order to apply the configuration of Example 8 to a DC grounded system that is grounded with high resistance, it is preferable to make the resistance value of the sensing circuits 411, 421 attached to the DC cable of the cable assembly 35 on the P-pole side larger than that of the sensing circuits 412, 422 attached to the cable assembly 36 on the N-pole side, thereby sufficiently reducing the closed circuit current.

[0046] 10. Example 9: Components of solar power generation systems, such as solar panels, cables, and junction boxes, are installed outdoors, creating a constant risk of ground faults. For this reason, many systems are equipped with insulation resistance measuring devices that continuously measure insulation resistance. Insulation resistance measuring devices continuously measure the insulation resistance of both the positive and negative poles in ungrounded and AC-grounded systems, and the positive pole in negative-pole grounded systems. Some insulation resistance measuring devices can set two or more reference resistance values ​​for alarm output. Such devices employ multiple reference values ​​(judgment reference values), such as a first reference value and a second reference value, and can output separate alarms when the measured resistance falls below the first reference value and when it falls below the second reference value. Furthermore, operation can be switched based on the reference value, such as issuing an alarm when the insulation resistance falls below the first reference value and forcibly shutting down the system when the insulation resistance falls below the second reference value. However, in actual systems, only one reference value is often used. For example, in many cases, only one of the reference values ​​is used to detect a decrease in insulation resistance and output an alarm about it, and the second and subsequent reference values ​​are not used. The anomaly detection device and anomaly detection method of this embodiment are also applicable to a photovoltaic power generation system equipped with a device capable of measuring two or more insulation resistance values ​​for ground fault detection. Figure 16 shows the configuration of a photovoltaic power generation system 18 to which the anomaly detection device and anomaly detection method of Example 9 are applied.

[0047] The circuit employed for the sensing circuits 411, 412, 421, and 422 in the ninth embodiment is a pure resistance R (sensing circuit 1050 in FIG. 15 ). The solar power generation system 18 is equipped with a multi-value insulation resistance measuring device 460. A resistance measuring unit 461 of the multi-value insulation resistance measuring device 460 measures and outputs the resistance between the cable assembly 35 (including the P-side DC cables 150, 250, ...) and the cable assembly 36 (including the N-side DC cables 160, 260, ...) and the ground via the ground terminal 303. This resistance value is compared in a comparison calculation unit 463 with a reference value output from a reference resistance value generating unit 462, which generates an impedance reference value Zs (its pure resistance value Rs) for detecting an abnormality. If the reference value is exceeded, an abnormality alarm is output from an alarm output terminal 464. On the other hand, the resistance measurement value Zpm (i.e., its pure resistance value Rpm) and Znm (pure resistance value Rnm) are compared in a comparison calculation unit 466 with a reference value Zg (pure resistance value Rg) output from a reference resistance value generation unit 465 for earth fault detection, and if the measurement value is below the reference value, a ground fault accident alarm is output from an alarm output terminal 467.

[0048] In this way, in a system equipped with a multi-value insulation resistance measuring device, one reference value is set to the insulation resistance alarm reference resistance value Rg, and the other reference value is set to the impedance reference value Zs (pure resistance value Rs) for abnormality detection of the present disclosure, thereby enabling abnormality detection without adding a separate monitoring processing unit 400. More specifically, if the resistance value of the detection circuit: Re, the abnormality detection reference value: Rs, the resistance measurements of the P-side and N-side DC cables respectively: Rpm, Rnm, and the insulation resistance alarm reference resistance value: Rg, then Re / 10<Rs<Re / 9 (6) Rg<Re / 10 (7) It is possible to distinguish between abnormality detection and ground fault detection by setting the following.

[0049] The ninth embodiment can achieve the following unique effects. First, in a photovoltaic power generation system already equipped with an insulation resistance measuring device, abnormalities can be detected without the need to newly install a monitoring processing unit 400. Second, as in the eighth embodiment, by sufficiently increasing the pure resistance, both the positive-side DC cable and the negative-side DC cable are grounded with high resistance, which is essentially equivalent to being insulated, making it applicable to an ungrounded photovoltaic power generation system. Third, as in the eighth embodiment, the sensing circuit is a pure resistor, making it applicable to a DC-grounded system grounded with high resistance, and the high resistance of the grounding resistor and the high resistance of the sensing circuit can be shared. To apply the configuration of the ninth embodiment to a DC-grounded system grounded with high resistance, it is preferable to sufficiently reduce the closed-circuit current by increasing the resistance of the sensing circuits 411 and 421 attached to the DC cables of the positive-side cable assembly 35 compared to that of the sensing circuits 412 and 422 attached to the negative-side cable assembly 36. In Example 9, sensing circuits 411, 421 and 421, 422 are attached to both the positive and negative pole sides, respectively. However, even in a configuration where no sensing circuit is attached to the positive pole side and only 421, 422 are attached to the negative pole side, it is possible to detect abnormalities on the negative pole side.

[0050] In Examples 1 to 9, an impedance measurement circuit with two independent inputs was required to measure the impedance of each sensing circuit (e.g., sensing circuits 411, 412, 421, 422) connected between ground and cable assembly 35 made up of P-side DC cables 150, 250, ... or N-side cable assembly 36 made up of N-side DC cables 160, 260, .... This was because the DC potentials of each cable were different.

[0051] In contrast, in an anomaly detection device and an anomaly detection method according to a tenth embodiment of the present disclosure, an anomaly detection in both the P-side DC cable and the N-side DC cable cable assemblies is realized using a single impedance measurement circuit. FIG. 17 is a block diagram showing an example of a solar power generation system 20 to which the tenth embodiment is applied. The solar power generation system 20 includes a coupling capacitor 2001 having one end connected to a cable assembly 35 including the P-side DC cables 150, 250, etc., and a coupling capacitor 2002 having one end connected to an N-side cable assembly 36 including the N-side DC cables 160, 260, etc. The coupling capacitors 2001 and 2002 are connected in series, and their interconnection node serves as a measurement point for the impedance measurement circuit 401. The interconnection node between the coupling capacitors 2001 and 2002 is neutral in terms of potential and is therefore also referred to as the neutral point. In this configuration, the DC components of the P-side and N-side DC cables are isolated from each other by coupling capacitors 2001 and 2002. This allows a single impedance measurement circuit to measure the impedance of the sensing circuits 411, 412, 421, and 422 connected to both the P-side and N-side cable assemblies. For the P-side cable assembly 35, the measured impedance value is the composite impedance of a circuit in which the parallel connection of the sensing circuits 411 and 421 (generally n circuits) and the coupling capacitor 2001 are connected in series. Similarly, for the N-side cable assembly 36, the measured impedance is the composite impedance of a circuit in which the parallel connection of the sensing circuits 412 and 422 (generally n circuits) and the coupling capacitor 2002 are connected in series.

[0052] The coupling capacitors 2001 and 2002 connected in the solar power generation system 20 are also useful in a configuration in which a sensing circuit is attached to only one of the P-side cable assembly 35 and the N-side cable assembly 36. For example, many solar power generation systems are equipped with an insulation resistance meter to prevent ground faults. FIG. 18 is a block diagram showing an example solar power generation system to which this embodiment is applied. The solar power generation system 22 further includes an insulation resistance meter 2003 in addition to the solar power generation system 16 (FIG. 11). The insulation resistance meter 2003 has a configuration of the general neutral-grounded type disclosed in FIG. 13 of Patent Document 4. That is, the insulation resistance meter 2003 includes a pure resistor 2004 having one end connected to the P-side cable assembly 35 and a pure resistor 2005 having one end connected to the N-side cable assembly 36. The insulation resistance measuring instrument 2003 further includes a voltmeter 2006 that measures the voltage between the P-side cable assembly 35 and the N-side cable assembly 36, and an ammeter 2007 connected between their neutral points and ground. When the insulation of the P-side cable assembly 35 and the N-side cable assembly 36 is sound, the potential of the neutral point is equal to ground and zero, and no current flows through the ammeter 2007. However, if the insulation resistance value of the DC cable in either the P-side cable assembly 35 or the N-side cable assembly 36 decreases due to an insulation defect or the like, the potential of the neutral point shifts to the positive or negative side, generating a current between the neutral point and ground via the ammeter 2007. The insulation defect can be detected by measuring this current value. Furthermore, the insulation resistance value can be measured by measuring the voltage between the P-side cable assembly 35 and the N-side cable assembly 36 with the voltmeter 2006 and dividing the voltage value by the current value. In the configuration of photovoltaic power generation system 22 equipped with insulation resistance measuring instrument 2003, the neutral point is grounded via ammeter 2006, which has zero internal resistance, so that both P-side cable assembly 35 and N-side cable assembly 36 always generate a DC potential with respect to the ground. For example, in a large photovoltaic power generation system, many solar panels are connected in series to form a string, and the generated voltage can reach 1200V.In such a case, if the neutral point is grounded as in the solar power generation system 22, a DC voltage of +600 V is generated on the P-side cable assembly 35 and -600 V is generated on the N-side cable assembly 36 relative to the ground. The input of a circuit such as the impedance measurement circuit 401 generally cannot withstand high voltages and has low input impedance. Therefore, if a large-scale solar power generation system employs an impedance measurement circuit and a high DC potential is applied, the impedance measurement circuit may be destroyed by the large DC current. In the solar power generation system 22, installing coupling capacitors 2001 and / or 2002 prevents the application of DC voltage and protects the impedance measurement circuit. The sensing circuit applicable to Example 10 can be the same as the sensing circuits applied to Examples 1 to 5 and 9, provided that the sensing circuit is attached to both the P-side cable assembly 35 and the N-side cable assembly 36. However, if a pure resistor R is attached to the sensing circuit, it must have a sufficiently large resistance value to minimize leakage current. In a configuration in which a sensing circuit is provided only on either the P-side cable assembly 35 or the N-side cable assembly 36, all of the sensing circuits applied to the first to ninth embodiments are applicable.

[0053] 12. Example 11 In Examples 1 to 10, sensing circuits 411, 412, 421, and 422 are connected between the P-side cable assembly 35 or the N-side cable assembly 36 and the ground. Therefore, the DC cables of the cable assemblies 35 and 36 are grounded to the ground via the sensing circuits in a DC manner (Examples 3 to 5 and 7 to 9) or in an AC manner (Example 1 and Example 6). Some solar power plants have an electrical configuration in which grounding via the sensing circuits, i.e., neither AC grounding nor DC grounding, is desirable. Example 11 can accommodate a more flexible electrical configuration of a solar power plant.

[0054] FIG. 19 is a block diagram showing an example of a solar power generation system 24 to which Example 11 of this embodiment is applied. Comparing the solar power generation system 24 with the solar power generation system 90 of FIG. 1 , one end of coupling capacitors 2001 and 2002 is connected to each of cable assemblies 35 and 36, and an impedance measurement circuit 401 is connected to a neutral point, which serves as an interconnection (coupling node) connecting the coupling capacitors 2001 and 2002 in series. Meanwhile, one terminal of each of sensing circuits 411 and 412 is connected to the P-side and N-side DC cables 150, 150, respectively, connecting the sensing circuits 411 and 412 in series via an interconnection. This interconnection serves as a neutral point and is not grounded. The neutral points of the sensing circuits 411 and 412 are connected to the impedance measurement circuit 401 via a dedicated neutral conductor 2008. The same applies to the sensing circuits 421 and 422. Unlike Example 10 (FIG. 17), in which the impedance value measured by the impedance measurement circuit 401 is measured between the ground and the neutral, this example differs in that a neutral conductor 2008 connected to the neutral points of the sensing circuits 411 and 412 is utilized. Although none of the sensing circuits 411, 412, 421, and 422 are grounded in terms of either AC or DC, this configuration still enables detection of abnormalities in the cable assemblies 35 and 36. Examples of sensing circuits applicable to Example 11 include the sensing circuits applied to Examples 1 to 5 and 7 to 9. However, if a pure resistor R is added to the sensing circuit, it is necessary to add a sufficiently large resistance R to reduce leakage current.

[0055] 13. Example 12 In Examples 1 to 9, sensing circuits 411, 412, 421, and 422 are connected between the P-side cable assembly 35 or the N-side cable assembly 36 and the ground. In those examples, sensing circuits 411, 412, 421, and 422 are required to distinguish between the P-side and N-side DC cables 150, 250, 160, and 260 in each of the junction boxes 100 and 200 and detect abnormalities, and the number of sensing circuits is twice the number of installed junction boxes. Based on this, Example 12 has a configuration in which the required number of sensing circuits is the same as the number of junction boxes. FIG. 20 is a block diagram showing an example of a photovoltaic power generation system 26 to which this embodiment is applied. Compared to the photovoltaic power generation system 90 of FIG. 1 , in Example 12, a coupling capacitor 2001 is connected to couple the cable assembly 35 and one input of the impedance measurement circuit 401, and a coupling capacitor 2002 is connected to couple the cable assembly 36 and the other input of the impedance measurement circuit 401. Furthermore, one end of a sensing circuit 411 is connected to the P-side DC cable 150 and the other end is connected to the N-side DC cable 160. A sensing circuit 421 is connected to the P-side DC cable 250 and the other end is connected to the N-side DC cable 260. In this configuration, a series circuit is formed for the cable assembly 35, passing through the coupling capacitor 2001, the P-side DC cable 150, the sensing circuit 411, the N-side DC cable 160, and the coupling capacitor 2002. The same applies to the cable assembly 36. Each series circuit is connected in parallel to form a series-parallel circuit. The impedance measurement circuit 401 measures the impedance value of this series-parallel circuit. If an abnormality such as a break occurs in either the P-side DC cables 150, 250 or the N-side DC cables 160, 260, the corresponding parallel series circuit opens, causing a change in impedance value. The abnormality can be detected from this change in impedance value.

[0056] The photovoltaic power generation system 26 of Example 12 can achieve the following unique advantages. First, only one sensing circuit is required for each pair of P-side and N-side DC cables, thereby reducing costs. Second, the circuit for measuring impedance does not include a ground wire (as in Examples 1 to 9 and Example 10 of the previous application) or a neutral wire (as in Example 11), eliminating the need for these wires. Third, the impedance change per cable assembly during an abnormality is twice as large as in Examples 1 and 2 (e.g., Example 1, photovoltaic power generation system 12, Figure 2 ), which uses two sensing circuits, one for each P-side and N-side DC cable, thereby achieving a high signal-to-noise ratio. Examples of sensing circuits applicable to Example 12 include the sensing circuits applicable to Examples 1 to 5 and 7 to 9. However, if a pure resistor R is added to the sensing circuit, it is necessary to add a sufficiently large resistance R to reduce leakage current.

[0057] 14. Example 13 Example 13 is an improvement that includes a circuit to prevent surge current inflow and protect the input section. This is implemented in the photovoltaic power generation system 28A shown in FIG. 21. In actual photovoltaic power plants, power conditioners do not operate 24 hours a day due to the influence of the sun's diurnal motion. To explain this operation using the photovoltaic power generation system 12 shown in FIG. 2 as an example, the amount of solar radiation increases after sunrise. When the photovoltaic voltage reaches a predetermined level, the DC magnetic contactor 320 and the AC magnetic contactor 340 are closed, and power transmission operation begins. When the photovoltaic voltage falls below the predetermined level before sunset, the DC magnetic contactor 320 and the AC magnetic contactor 340 are opened, and power transmission operation is stopped. Large current changes occur when the DC magnetic contactor 320 and the AC magnetic contactor 340 are closed and opened. This causes large induced electromotive forces in the DC cables on both sides of the PN due to the self-inductance of each distribution line in the power conditioner 300 and the capacitance of the smoothing capacitor in the inverter unit 330. Furthermore, because photovoltaic power generation systems are installed outdoors, they are subject to frequent lightning strikes and induced lightning. For example, when lightning strikes the solar panel 1, a large surge current flows into the P-side DC cable 150, the N-side DC cable 160, or both. Furthermore, when induced lightning occurs due to a nearby lightning strike, a large surge voltage is induced in the P-side DC cable 150 or the N-side DC cable 160. When the electromagnetic contactors are opened or closed, such as when starting or stopping the power conditioner, or when lightning strikes or induced lightning occurs, including in other embodiments, a large surge voltage is induced in the input section of the impedance measurement circuit 401 connected to the P-side DC cable 150 or the N-side DC cable 160 (in Examples 1 to 9, 10, and 11 of the present invention), and also in another input section of the impedance measurement circuit 401 connected to the neutral line (in Example 11). The impedance measurement circuit 401 has a small input impedance. Therefore, there is a concern that the induced surge voltage will cause a large surge current to flow in, easily destroying the system.

[0058] The configuration of a photovoltaic power generation system 28A of Example 13 will be described in comparison with Example 10 (photovoltaic power generation system 20 in FIG. 17 ). Although multiple solar panels, such as solar panels 1 and 2, can be connected to the photovoltaic power generation system 28A, FIG. 21 focuses on only solar panel 1. As described in Example 10, coupling capacitors 2001 and 2002 of the photovoltaic power generation system 28A are capacitors for DC-insulating the impedance measurement circuit 401 from the DC voltage applied to the P-side DC cable and the N-side DC cable. A resistor 2010 (neutral-grounded resistor) is connected in series between the neutral point to which the coupling capacitors 2001 and 2002 are connected and the ground, and the potential difference across resistor 2009 is measured by the impedance measurement circuit 401. When the electromagnetic contactor is opened or closed during power conditioner startup or shutdown, or when lightning strikes or induced lightning strikes, a surge voltage may be induced unevenly on either the positive or negative DC cable. In this case, a large charge is electrostatically induced unevenly on either coupling capacitor 2001 or 2002. As a result, the potential at the neutral point between coupling capacitors 2001 and 2002 may rise. In such cases, installing a gas discharge tube (GDT) 2009 can suppress the voltage rise by gas discharge. Furthermore, connecting resistor 2010 supplies charge from the ground, preventing the neutral point potential from rising. Note that if the neutral point is grounded without resistor 2010, it will be at the same potential as the ground, making impedance measurement impossible.

[0059] In photovoltaic power generation system 28A, one end of inductor 2011 is connected to the neutral point, and the other end is connected to another inductor (inductor for preventing surge voltage inflow) 2014. Inductor 2014 is further coupled to an impedance measurement input of impedance measurement circuit 401. One end of either or both of Zener diode 2012 and varistor 2013 is connected to the junction of inductors 2011 and 2014, and the other ends thereof are grounded.

[0060] The surge voltage that needs to be prevented from entering the input section of the impedance measurement circuit 401 has a large high-frequency component. Since the impedance of the inductors 2011 and 2014 increases inversely proportional to the frequency, inserting these in series makes it possible to prevent the high-frequency component of the surge voltage from entering the input of the impedance measurement circuit.

[0061] The Zener diode 2012 and varistor 2013 are provided to bypass a surge voltage to the ground by turning on when the surge voltage occurs, thereby mitigating its intrusion into the next-stage inductor 2014. Therefore, either the Zener diode 2012 or the varistor 2013 may be used alone. The junction of the Zener diode 2012 also functions as a capacitor. Therefore, the circuit composed of the inductor 2011, the Zener diode 2012, the varistor 2013, and the inductor 2014 forms an LCL (T-type) filter, a type of high-frequency filter, and can remove the high-frequency components of the surge voltage as a whole. The circuit composed of the coupling capacitor 2001 to the inductor 2014 functions as a pre-stage circuit to the input section of the impedance measurement circuit 401 and is applicable to Examples 1 to 8. The circuit composed of the inductor 2011 to the inductor 2014 is applicable to Example 9.

[0062] 15. Example 14 FIG. 22 is a block diagram showing an example of a photovoltaic power generation system 28B to which Example 14 of this embodiment is applied. In the photovoltaic power generation system 24 (Example 11, FIG. 19), the neutral conductor 2008 is also floating above the ground, which can cause surge current intrusion and surge voltage induction. Therefore, surge current can also intrude into the input section of the impedance measurement circuit 401 that receives input from the neutral conductor. Example 11 is an invention in which one end of the sensing circuits 411 and 412 cannot be grounded. However, if grounding is possible near the impedance measurement circuit 401, in Example 14, a surge current protection circuit similar to that of Example 13, consisting of a GDT 2009, resistor 2010, and inductor 2014, is installed on the input side of the neutral conductor 2008. This protects the input section of the impedance measurement circuit 401.

[0063] 16. Example 15 Example 15 relates to a circuit that prevents surge voltages and currents from entering the input section of the impedance measurement circuit 401 in Example 12, with the aim of protecting the input section. FIG. 23 is a block diagram showing a photovoltaic power generation system 28C as an example to which Example 15 of this embodiment is applied. In photovoltaic power generation system 28C, a surge current protection circuit consisting of GDT 2009 and resistor 2010 to inductor 2014 of photovoltaic power generation system 28A ( FIG. 21 ) in Example 13 is combined with the connection configuration of sensing circuit 411 of photovoltaic power generation system 26 ( FIG. 20 ) in Example 12, with the connection of coupling capacitors 2001 and 2002 changed. Even with this configuration, the effect of protecting the impedance measurement circuit 401 can be achieved, similar to Examples 13 and 14.

[0064] 17. Example 16 Example 16 is implemented using a photovoltaic power generation system with limited operating time. Figure 24 is a block diagram showing an example of a photovoltaic power generation system 28D to which Example 16 of this embodiment is applied. In addition to surge voltages due to lightning strikes, induced lightning, and DC contactor activation, the solar panels generate rated photovoltaic power during high daytime solar radiation intensity, resulting in a large DC voltage of 600 to 1000 V applied between the P-side and N-side DC cables. Meanwhile, the applied voltage is low during the period from sunset to sunrise when solar radiation intensity is low. Regarding theft prevention, one of the main objectives of the present invention, since theft primarily occurs at night, the objective may be sufficiently achieved by operating the anomaly detection device of the present invention only during the period from sunset when the photovoltaic power generation system is shut down until sunrise when it is started up again. Therefore, in this example, the operating time of the impedance measurement circuit 401 is limited. Even without sunlight, the solar panels generate electromotive force, applying DC voltage to the DC cable. Therefore, limiting the operating time of the impedance measurement circuit 401 has the advantage of preventing damage to the impedance measurement circuit 401 .

[0065] In actual operation, when an abnormality is detected, it is necessary to issue an alarm and take countermeasures (such as sounding the horn, illuminating the area with light, or reporting to a remote monitoring agency). Therefore, in order to achieve these, it is desirable to install an alarm device.

[0066] Example 16 embodies these devices. In Fig. 24 , a relay 3001 synchronized with the AC electromagnetic contactor 340 of the power conditioner 300 is provided to limit the operation of the impedance measurement circuit 401 to the period from sunset to sunrise, which is the period during which power transmission operation due to sunlight in the solar power generation system is stopped. The relay 3001 is set to be closed when the AC electromagnetic contactor 340 is opened. When the relay 3001 is closed, power such as 100 VAC is supplied from the AC power cable 3010 to the impedance measurement circuit 401, and the circuit starts operating.

[0067] If the change in the impedance value measured by the impedance measurement circuit 401 exceeds a reference value, a signal indicating this is issued from the impedance measurement circuit 401 and transmitted to relays 3101 and 3111. The contacts of relays 3101 and 3111 are closed, activating alarms 3102 and 3112, which are deterrent devices. As alarms, for example, patrol lights or remote warning communication devices are used. Note that the number of relays and alarms is not limited to two, and any required number can be connected in parallel.

[0068] After sunset, when the photovoltaic power of the solar panels falls below the rated voltage, the DC and AC electromagnetic contactors 320 and 340 open, shutting down the solar power generation system. However, DC voltage may still be applied to the DC cable. This is because the photovoltaic power of the solar panels generates DC voltage as long as light is irradiated, such as during twilight, even after sunset. For this reason, as in solar power generation system 28C, it is preferable to use a delay timer switch 3003 inserted in the connecting wire 3002 connecting the DC cables 150 and 160 to the impedance measurement circuit 401. The delay timer switch 3003 can close itself when the DC voltage on the DC cable becomes sufficiently low. Specifically, the delay timer switch 3003, represented by the symbol of a timer relay, contains a timer device for timing the delay time until a certain time has elapsed after the relay 3001 is closed and AC power is supplied, and a relay unit that can open and close based on a signal from the timer device. The interruption of power supply from the AC power source is linked to a decrease in the amount of solar radiation, and the signal issued by the timer device in the delay timer switch 3003 functions as a monitoring start signal. By employing the delay timer switch 3003 that operates in this manner, it is possible to avoid the influence of photovoltaic power due to twilight, etc., at the timing of connecting the P-side DC cable 150 and the N-side DC cable 160 to the impedance measurement circuit 401. As a result, the impedance measurement circuit 401 can be appropriately protected. Furthermore, by inserting a fuse 3004 into the connecting wire 3002, the fuse 3004 can blow to protect the impedance circuit in the event of an excessive surge current.

[0069] In the photovoltaic power generation system 28D of Example 16, the delay timer switch 3003 is installed. Due to the action of a timer device built into the delay timer switch 3003, when the delay timer switch 3003 is open, the connection between the DC cables 150 and 160 and the impedance measurement circuit 401 is severed, resulting in a very large impedance measurement value measured by the impedance measurement circuit 401. This can cause a very large discrepancy between the impedance measurement value measured when the delay timer switch 3003 is closed and the impedance of the sensing circuits 411 and 412 is measured and the impedance measurement value measured when the delay timer switch 3003 is open, potentially resulting in unstable operation of the impedance measurement circuit 401. To prevent this, it is also useful to install a dummy sensing circuit 3005 with an impedance value close to the impedance values ​​of the sensing circuits 411 and 412 in the photovoltaic power generation system 28D. This allows the impedance circuit 401 to measure the impedance of the dummy sensing circuit 3005 when the delay timer switch 3003 is open, thereby stabilizing operation.

[0070] 18. Example 17 Like Example 16, Example 17 is implemented using a solar power generation system with limited operating time. FIG. 25 is a block diagram showing an example solar power generation system 28E to which Example 17 of this embodiment is applied. This example can also be adopted in systems with multiple solar panels in addition to solar panel 1, but is omitted due to the repetitive configuration. Like Example 16, Example 17 aims to avoid damage caused by the application of high voltage. In Example 17, the operating time of the sensing circuit in the connection box 100 is limited to the period from sunset to sunrise, when the solar radiation intensity is low and the applied voltage from the solar panel is low, thereby reducing the time during which DC voltage is applied to the sensing circuit. In the solar power generation system 28E of FIG. 25, a P-side relay 4001 (P-side switch) is additionally installed between the P-side DC cable 150 and the sensing circuit 411. In the solar power generation system 28E, an N-side relay 4002 (N-side switch) is additionally installed between the N-side DC cable 160 and the sensing circuit 412, which is installed between the N-side DC cable 160 and the ground. The solar power generation system 28E also includes a DC / DC converter power supply 4003 (switch control unit). The DC power input terminals (P pole, N pole) of the DC / DC converter power supply 4003 are electrically connected to the P-side DC cable 150 and the N-side DC cable 160 of the solar panel, respectively, and power is supplied from the solar panel. The output terminals of the DC / DC converter power supply 4003 are connected to the contact opening / closing signal input terminals of the P-side relay 4001 and the N-side relay 4002. The voltage applied from the solar panel 1 is approximately the rated voltage (600 to 1000 V) from sunrise to sunset due to sunlight irradiation, and then decreases to 0 to 600 V from sunset to sunrise. The DC / DC converter power supply 4003 is set so that when a high solar panel voltage from sunrise to sunset is input thereto, a voltage (e.g., 24 V) that opens the relay contacts is output, and when a low solar panel voltage from sunset to sunrise is input thereto, no voltage that opens the relay contacts is output. As a result, the sensing circuits 411, 412 are electrically connected to the P-side DC cable 150 and the N-side DC cable 160 only during the period from sunset to sunrise.As a result, during the time from sunrise to sunset when the solar panel voltage is high, high voltage from the solar panel is not applied to the detection circuits 411, 412. In this way, damage caused by continuous application of high voltage can be avoided in the detection circuits 411, 412. The P-side relay 4001 and the N-side relay 4002 function as a P-side switch and an N-side switch, respectively, and the DC / DC converter power supply 4003 functions as a switch control unit.

[0071] 19. Example 18 Like Examples 16 and 17, Example 18 is implemented using a solar power generation system with a limited operating time. FIG. 26 is a block diagram showing an example solar power generation system 28F to which Example 18 of this embodiment is applied. This example can also be adopted in a system with multiple solar panels in addition to solar panel 1, but due to the repetitive configuration, it is omitted here. In Example 18, the operating time of the impedance measurement circuit 401 is limited. Even without sunlight, electromotive force is generated in the solar panel, and a DC voltage is applied to the DC cable. Therefore, limiting the operating time of the impedance measurement circuit 401 has the advantage of preventing damage to the impedance measurement circuit 401. In the solar power generation system 28F of FIG. 26, a P-side relay 4011 (P-side switch) is additionally installed between the coupling capacitor 2001 connected to the P-side DC cable 150 and the impedance measurement circuit 401. In the photovoltaic power generation system 28F, an N-side relay 4012 (N-side switch) is additionally provided between the coupling capacitor 2002 connected to the N-side DC cable 160 and the impedance measurement circuit 401. In the photovoltaic power generation system 28F, a DC / DC converter power supply 4013 (switch control unit) is also provided. The DC / DC converter power supply 4013 is electrically connected to the P-side DC cable 150 and the N-side DC cable 160 that run from the solar panel 1 to the power conditioner 300. The DC / DC converter power supply 4013 can be configured similarly to the DC / DC converter power supply 4003 in Example 17. That is, the DC / DC converter power supply 4013 is configured so that when a high solar panel voltage from sunrise to sunset is input thereto, a voltage that opens the relay contacts is output, and when a low solar panel voltage from sunset to sunrise is input thereto, a voltage that opens the relay contacts is not output. As a result, the impedance measuring circuit 401 is electrically connected to the P-side DC cable 150 and the N-side DC cable 160 only during the period from sunset to sunrise.As a result, during the time from sunrise to sunset when the solar panel voltage is high, a high solar panel voltage is not applied to the impedance measurement circuit 401 or the coupling capacitors 2001 and 2002, preventing these devices and elements from being damaged by the continuous application of high voltage. The P-side relay 4011 and the N-side relay 4012 function as a P-side switch and an N-side switch, respectively, and the DC / DC converter power supply 4013 functions as a switch control unit.

[0072] 20. Summary of Applicability of Examples The present embodiment has been described above based on examples in accordance with the classification of grounded types of photovoltaic power generation systems. Table 1 shows the applicability of the anomaly detection device and anomaly detection method of Examples 1 to 9 of the present disclosure to each grounded type. Furthermore, the anomaly detection devices and anomaly detection methods of Examples 10 to 18 of the present disclosure can be applied to any of the grounded types in Table 1. The anomaly detection device and anomaly detection method of the present embodiment can be applied to any of the grounded type photovoltaic power generation systems by using different sensing circuits according to the applicability shown in Table 1, for example.

[0073] 21. Conclusion The present disclosure is not limited to the above-described examples and includes various modifications. For example, the above-described examples have been described in detail to clearly explain the present disclosure, and are not necessarily limited to those including all of the described configurations. It is possible to replace a portion of the configuration of one example with a configuration of another example, or to add a configuration of another example to a configuration of one example. Furthermore, it is possible to add, delete, or replace a portion of the configuration of each example with another configuration. In other words, those skilled in the art may make various modifications, combinations, subcombinations, and substitutions of the components of the above-described embodiments within the technical scope of the present invention or its equivalents. In fact, the configurations of the sensing circuit attached to the P-side DC cable and the sensing circuit attached to the N-side DC cable can be selected arbitrarily as long as there is no functional contradiction.

[0074] 90, 12, 14, 16, 18, 20, 22, 24, 26, 28A, 28B, 28C, 28D Solar power generation system 1, 2 Solar panel 100, 200 Connection box 101, 102, 201, 202, 310, 311 Fuses 103, 203 Switches 150, 250 P-side DC cables 160, 260 N-side DC cables 30 DC power transmission section 35 Cable assembly (P-side) 36 Cable assembly (N-side) 300 Power conditioner 301 DC input terminal (P-terminal) 302 DC input terminal (N-terminal) 303 Ground terminal 320 DC electromagnetic contactor 330 Inverter section 340 AC electromagnetic contactor AC side switching device.400 Monitoring processing unit 401 Impedance measurement circuit 402 Abnormality detection processing unit 403 Alarm output circuit 404 Alarm output terminal 411, 421 Detection circuit (P-side detection circuit) 412, 422 Detection circuit (N-side detection circuit) 413, 423, 414, 424 Detection circuit (with diode) 460 Multi-value insulation resistance device 461 Resistance measurement unit 462 Reference resistance value generation unit (for abnormality detection) 463, 466 Comparison operation unit 464, 467 Alarm output terminal 465 Reference resistance value generation unit (for earth fault detection) 500 Step-up transformer 600 System power network 700 N-side grounding circuit 1000 RLC series resonant circuit 1010 Resistor-diode series circuit 1020 RLC parallel anti-resonant diode series circuit 1030 RLC parallel anti-resonant circuit 1040 L-parallel RLC series resonant circuit 1050 Pure resistance circuit 2001, 2002 Coupling capacitor 2003 Insulation resistance measuring instrument 2004, 2005 Pure resistor 2006 Voltmeter 2007 Ammeter 2008 Neutral wire 2009 GDT (Gas Discharge Tube) 2010 Resistor (neutral grounding resistor) 2011 Inductor (for preventing surge voltage inflow) 2012 Zener diode 2013 Varistor 2014 Inductor (for preventing surge voltage inflow) 3001, 3101, 3111 Relay 3002 Connecting wire 3003 Delay timer switch 3004 Fuse 3005 Dummy detection circuit 3010 AC power cable 3102, 3112 Alarm (deterrent device) 4001, 4011 P-side relay (P-side switch) 4002, 4012 N-side relay (N-side switch) 4003, 4013 DC / DC converter power supply (switch control unit).

Claims

1. An abnormality detection device for a DC power transmission section that transmits DC power output from at least one solar panel, comprising: at least one sensing circuit having two terminals and exhibiting a predetermined impedance, the at least one sensing circuit including at least one of a resistor, a capacitor, and an inductor, one of the two terminals being electrically connected to at least one of the conductors for DC transmission provided in the DC power transmission section; a measuring device electrically connected to the conductor for measuring the DC transmission section impedance exhibited by the conductor and the sensing circuit; and an abnormality detection processing section that detects an abnormality in the DC power transmission section by comparing the DC transmission section impedance measured by the measuring device with a judgment reference value.

2. The abnormality detection device according to claim 1, wherein the other of the two terminals of the sensing circuit is electrically grounded, and the impedance of the DC transmission section is a value that the conductor and the sensing circuit exhibit between the conductor and the ground.

3. The abnormality detection device according to claim 1, wherein the at least one solar panel forms a plurality of groups, each group including at least one solar panel, the DC power transmission unit includes a cable assembly in which the conductors are electrically connected in parallel to aggregate DC transmission outputs from each group of solar panels, the sensing circuits are provided corresponding to at least one of the groups of solar panels, and the one terminal of each sensing circuit is electrically connected to a position of the conductor of the cable assembly that is connected to the group of solar panels to which the sensing circuit belongs, and the abnormality detection processing unit detects an abnormality in the DC power transmission unit by including a value for specifying a numerical range of the DC transmission unit impedance when the DC power transmission unit and the sensing circuit are all normal as at least a part of the judgment reference value.

4. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit includes a capacitor and an inductor connected in series between the two terminals.

5. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit includes a diode connected in series between the two terminals so as to be reverse biased.

6. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit includes a capacitor and an inductor connected in parallel with each other between the two terminals.

7. An abnormality detection device as claimed in any one of claims 1 to 3, wherein the sensing circuit includes a circuit between the two terminals in which a first inductor and a series section in which a capacitor and a second inductor are connected in series are connected in parallel to each other.

8. The abnormality detection device according to claim 6, wherein the sensing circuit is configured such that the one terminal and the other terminal of the two terminals are connected in series with the inductor and diode, and the diode is oriented so as to be reverse biased.

9. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit connects the one terminal and the other terminal of the two terminals together via a resistor.

10. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit is a resonant circuit.

11. The abnormality detection device according to any one of claims 1 to 3, wherein the sensing circuit is an anti-resonant circuit.

12. An abnormality detection device as described in any one of claims 1 to 3, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel, and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, and the one terminal of the sensing circuit is connected to at least one of the P-side cable and the N-side cable.

13. The abnormality detection device according to claim 12, wherein the one terminal of the sensing circuit is connected to both the P-side cable and the N-side cable.

14. The abnormality detection device as described in claim 6, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, and the one terminal of the sensing circuit is connected to the N-side cable.

15. The abnormality detection device according to claim 1, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel, and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, the detection circuit includes a P-side detection circuit connecting the one terminal to the P-side cable, and an N-side detection circuit connecting the one terminal to the N-side cable, the P-side detection circuit and the N-side detection circuit have the other of the two terminals electrically grounded, the P-side cable and the N-side cable are connected by two coupling capacitors connected in series, and the measuring device measures the impedance value between the interconnection between the two coupling capacitors and the ground.

16. The abnormality detection device according to claim 1, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, the sensing circuit includes a P-side sensing circuit having one terminal connected to the P-side cable and an N-side sensing circuit having one terminal connected to the N-side cable, wherein other terminals of the P-side sensing circuit and the N-side sensing circuit are connected to each other, the P-side cable and the N-side cable are connected by two coupling capacitors connected in series, and the measuring device measures the impedance value between the interconnection portion of the other terminals of the P-side sensing circuit and the N-side sensing circuit and the interconnection portion of the two coupling capacitors.

17. The abnormality detection device as described in claim 1, wherein one of the two terminals is connected to one conductor for DC transmission and the other of the two terminals of the sensing circuit is connected to the other conductor for DC transmission, the measuring device is electrically connected to each of the one conductor for DC transmission and the other conductor for DC transmission via a coupling capacitor, and the measuring device measures the impedance value of the sensing circuit.

18. The abnormality detection device according to claim 2, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, the detection circuit includes a P-side detection circuit having one terminal connected to the P-side cable and an N-side detection circuit having one terminal connected to the N-side cable, wherein other terminals of the P-side detection circuit and the N-side detection circuit are both grounded, the P-side cable and the N-side cable are connected by two coupling capacitors connected in series, the interconnection part of the two coupling capacitors is grounded through a parallel circuit of a GDT and a resistor, the interconnection part is electrically connected to the measuring device via two inductors included in a T-type high-frequency filter, and the measuring device measures the impedance of the parallel circuit of the P-side detection circuit and the N-side detection circuit.

19. The DC transmission unit includes a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel, and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel; the sensing circuit includes a P-side sensing circuit having one terminal connected to the P-side cable, and an N-side sensing circuit having one terminal connected to the N-side cable, wherein other terminals of the P-side sensing circuit and the N-side sensing circuit are connected to each other; the P-side cable and the N-side cable are connected by two coupling capacitors connected in series; the interconnection portion of the two coupling capacitors is grounded through a parallel circuit of a GDT and a resistor; and the interconnection portion is electrically connected to one input of the measuring device through two inductors included in a T-type high-frequency filter; 2. The abnormality detection device according to claim 1, wherein the interconnection between the P-side sensing circuit and the N-side sensing circuit is electrically connected to another input of the measuring device via a GDT, a ground resistor, or two inductors forming a T-type high-frequency filter, or a parallel circuit of any two or more of these, and the measuring device measures an impedance value between the interconnection between the other terminals of the P-side sensing circuit and the N-side sensing circuit and the interconnection between the two coupling capacitors.

20. The abnormality detection device as described in claim 1, wherein one of the two terminals of the sensing circuit is connected to one conductor for DC transmission and the other of the two terminals is connected to the other conductor for DC transmission, the one conductor for DC transmission is grounded through a coupling capacitor and a parallel circuit of a GDT and a resistor, and the other conductor for DC transmission is grounded through a coupling capacitor, one end of the parallel circuit is electrically connected to one input of the measuring device through two inductors included in a T-type high-frequency filter, and the other end of the parallel circuit is electrically connected to the other input of the measuring device, and the measuring device measures the impedance value of the sensing circuit.

21. The abnormality detection device according to claim 18, further comprising a switch provided in an electrical connection path between the interconnection between the coupling capacitors and the resistor, the switch being closed after power transmission operation is stopped in accordance with the amount of sunlight.

22. The abnormality detection device as described in claim 21, wherein the switch comprises: a timer device that issues a monitoring start signal when a predetermined delay time has elapsed from the timing at which power transmission operation is stopped in accordance with the amount of sunlight; and a relay unit that receives the monitoring start signal from the timer device and closes.

23. The abnormality detection device according to claim 2, wherein the DC transmission unit comprises a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel, and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel, the sensing circuit includes a P-side sensing circuit having one terminal connected to the P-side cable, and an N-side sensing circuit having one terminal connected to the N-side cable, wherein the P-side sensing circuit is connected to the ground via a P-side switch, and the N-side sensing circuit is connected to the ground via an N-side switch, and further comprises a switch control unit having an input side connected to the P-side cable and the N-side cable and an output side connected to the P-side switch and the N-side switch, and operating in response to a voltage between the P-side cable and the N-side cable, wherein the switch control unit controls the P-side switch and the N-side switch so that they both open when the voltage on the input side rises, and both close when the voltage on the input side drops.

24. The DC transmission unit includes a P-side cable that can be electrically connected to the positive electrode of the at least one solar panel, and an N-side cable that can be electrically connected to the negative electrode of the at least one solar panel; the sensing circuit includes a P-side sensing circuit having one terminal connected to the P-side cable, and an N-side sensing circuit having one terminal connected to the N-side cable, wherein other terminals of the P-side sensing circuit and the N-side sensing circuit are both grounded; a P-side coupling capacitor having one terminal connected to the P-side cable and the other terminal connected to ground via a P-side switch; an N-side coupling capacitor having one terminal connected to the N-side cable and the other terminal connected to ground via an N-side switch; and a switch control unit having an input side connected to the P-side cable and the N-side cable, and an output side connected to the P-side switch and the N-side switch, and operating according to the voltage between the P-side cable and the N-side cable, 3. The abnormality detection device according to claim 2, wherein the switch control unit controls the P-side switch and the N-side switch so as to both open when the voltage on the input side rises and to both close when the voltage on the input side drops.

25. An abnormality detection method for a DC power transmission unit that transmits DC power output from at least one solar panel, wherein the DC power transmission unit is provided with at least one two-terminal sensing circuit that includes at least one of a resistor, a capacitor, and an inductor and exhibits a predetermined impedance, with one of the two terminals being electrically connected to at least one of the conductors for DC transmission provided in the DC power transmission unit, the abnormality detection method comprising the steps of: measuring the DC transmission unit impedance exhibited by the conductor and the sensing circuit with a measuring device electrically connected to the conductor; and comparing the DC transmission unit impedance with a judgment reference value, and generating and outputting an abnormality detection signal indicating an abnormality in the DC transmission system by an abnormality detection processing unit.

26. The abnormality detection method according to claim 25, wherein the other of said two terminals is electrically grounded, and said DC transmission section impedance is a value that said conductor and said sensing circuit exhibit between said conductor and ground.

27. The anomaly detection method according to claim 25, further comprising the step of: outputting an alarm output based on the anomaly detection signal.

28. The abnormality detection method described in claim 25, further comprising the steps of: stopping power transmission operation from the at least one solar panel in accordance with the amount of sunlight; establishing an electrical connection from the measuring device to the sensing circuit after the power transmission operation has stopped; and the measuring device starting operation.

29. The abnormality detection method as described in claim 28, further comprising the step of: issuing a monitoring start signal when a predetermined delay time has elapsed since the power transmission operation was stopped; and wherein the step of establishing an electrical connection is a step of receiving the monitoring start signal and establishing an electrical connection from the measuring device to the sensing circuit.

30. The abnormality detection method described in claim 26, further comprising the steps of: disconnecting an electrical connection between the sensing circuit and the ground in response to an increase in the output voltage of the at least one solar panel; and establishing an electrical connection between the sensing circuit and the ground in response to a decrease in the output voltage of the at least one solar panel.

31. The anomaly detection method described in claim 25, further comprising the steps of: disconnecting an electrical connection between the measurement device and the conductor in response to an increase in the output voltage of the at least one solar panel; and establishing an electrical connection between the measurement device and the conductor in response to a decrease in the output voltage of the at least one solar panel.

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