Photovoltaic fast turn-off and arc sensing system

Abstract

The present disclosure provides a system, apparatus, and method for providing fast turn-off for a photovoltaic power system, and provides a system, apparatus, and method for providing arc sensing for a photovoltaic power system. Alternating current can be input on the direct current bus to control the photovoltaic panel to be turned off. Local mean decomposition may be used to sense arcs on a direct current bus.

Description

Cross-references to related patent applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 329,169 filed on April 8, 2022, U.S. Provisional Patent Application No. 63 / 347,293 filed on May 31, 2022, and U.S. Provisional Patent Application No. 63 / 348,284 filed on June 2, 2022, the contents of which are incorporated herein by reference. Technical Field

[0002] This document relates to solar energy safety features, and more particularly to a safety system for photovoltaic panels. Background Art

[0003] This section is intended to provide a background or context to the invention described in the claims. The description herein may include concepts that could be pursued, but not necessarily concepts that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

[0004] Poor electrical connections in high voltage systems (such as solar panel buses) can result in arcing at poor or bad contact or connection points. Such arcing can result in circuit damage and / or fire.

[0005] In the United States, safety standards (UL 1741) have been established for photovoltaic (PV) systems, including the provision of rapid shutdown systems (PVRSS), and the American National Standard (ANSI / UL 1699) has been established for Arc-Fault Circuit Interrupters (AFCI). The standard requires that when in protection mode, the photovoltaic system should not provide a voltage exceeding 30V within 30 seconds outside the photovoltaic boundary and provide no more than 80V within the boundary. The protection mode can usually be initiated using a safety switch outside the building, for example, when a firefighter or roof repair worker plans to approach the roof of a building where a photovoltaic system is installed.

[0006] Known PVRSS systems involve providing signal transmission between a protection mode controller and an electronic controller that controls a switch to disconnect the photovoltaic panel in response to the signal transmission. When sunlight is shining, each photovoltaic panel will produce a low DC voltage, and the panels are connected in series to the power bus to reduce the current level on the power bus. The result of connecting multiple panels in series is that the voltage is much greater than 80V, and therefore it is necessary to provide disconnect switches at multiple locations in the photovoltaic panel string, rather than at each photovoltaic panel. The cost of providing a reliable electronic controller to control the switch to disconnect the photovoltaic panel in response to the signal transmission is an issue.

[0007] Furthermore, arc detection in photovoltaic (PV) systems is a requirement for future solar designs due to new hazards (particularly fire) that can occur in photovoltaic solar panel installations.

[0008] In addition, in order to prevent the risk of fire or damage resulting from a permanent open circuit, it is necessary to detect the arc at the beginning of the arc and open the photovoltaic circuit so that the arc stops. Opening the photovoltaic circuit based on arc sensing usually involves including a separately controlled switch, which increases the cost of the photovoltaic system. Summary of the invention

[0009] Applicants have discovered that arc sensing circuits can be isolated from the photovoltaic DC bus using a transformer shared with a passive circuit connected to the photovoltaic power bus, and that the arc sensing circuits can be remotely driven using an AC power source, with the passive circuit providing a gate signal to a normally open switch that connects the photovoltaic panel to the bus. In this way, arc sensing is not affected by the AC power source, and the shutoff of the AC power source can cause the normally open switch to open, thereby disconnecting the photovoltaic panel from the bus to meet safety requirements.

[0010] In a broad aspect, the present disclosure provides an isolation switch device for a photovoltaic (PV) panel, comprising: an AC coupler and a bandpass filter connected in series between an input and an output of the device; a rectifier gate signal circuit connected to the AC coupler and providing a switch gate signal; and at least one normally open switch connected in parallel with the bandpass filter, the gate of the at least one normally open switch being connected to the switch gate signal.

[0011] In some embodiments, the bandpass filter of the isolation switch may be operated to pass AC current in the range of 200 kHz to 300 kHz.

[0012] In one embodiment, the AC coupler of the isolation switch may be a transformer. In some examples of the present disclosure, the normally open switch includes a pair of normally open switches connected in parallel with the band pass filter.

[0013] In a broad aspect, the present disclosure provides a photovoltaic (PV) rapid shutdown system. The system includes: an AC power source, providing AC current; an AC injector, for coupling the AC current to a DC bus of a photovoltaic panel array; a shutdown control input, associated with one of the AC power source and the AC injector, for interrupting the supply of the AC current to the DC bus; and at least one isolation switch device as defined in different variations of the present application.

[0014] In a broad aspect, the present disclosure provides a photovoltaic (PV) rapid shutdown and arc sensing system, comprising: an AC power source providing an AC current; an arc sensing circuit having an output portion indicating an arc; an AC injection transformer (ACinjector transformer) for coupling the AC current to a DC bus of a photovoltaic panel array, the AC injection transformer having a first winding connected to the AC power source, a second winding connected to the DC bus, and a third winding connected to the arc sensing circuit and having turns in a direction opposite to the direction of the turns of the first winding; a shutdown control input portion associated with one of the AC power source and the AC injector for interrupting the supply of AC current to the DC bus, the shutdown control input portion being connected to the output portion of the arc sensing circuit; and at least one isolation switch device, comprising: an AC coupler and a bandpass filter connected in series between the input and output portions of the device; a rectifier gate signal circuit connected to the AC coupler and providing a switch gate signal, and at least one normally open switch connected in parallel with the bandpass filter, the gate of the at least one normally open switch being connected to the switch gate signal.

[0015] In some embodiments, the rapid shutdown system may have a photovoltaic panel array connected to a DC bus, with an AC power source providing less than 20 mW per meter of power to the DC bus in the photovoltaic panel array.

[0016] In another broad aspect, the present disclosure provides a method for providing emergency de-energizing of a photovoltaic panel. The method includes: injecting an alternating current on a DC bus of a photovoltaic panel array; isolating the AC current from the DC bus; and using the isolated AC current to cause a passive circuit to allow DC current to flow from the photovoltaic panel through the DC bus, wherein interruption of the AC current provides emergency de-energizing of the DC bus.

[0017] In some examples, using isolated AC current to supply power to a passive circuit to allow DC current to flow from a photovoltaic panel through a DC bus can include: receiving the isolated AC current through a rectifier gate signal circuit that provides a switch gate signal; and using the switch gate signal to turn on at least one normally open switch to allow DC current to flow from the photovoltaic panel through the DC bus; wherein when the AC current is interrupted, the at least one normally open switch opens and stops the DC current from flowing through the DC bus.

[0018] In some examples of the method, isolating the AC current from the DC bus includes isolating the AC current using a transformer.

[0019] In some examples of the method, injecting the AC current on a DC bus of the photovoltaic panel array includes injecting the AC current at a frequency different than an operating frequency of an inverter receiving the DC voltage.

[0020] In another broad aspect, the present disclosure provides a photovoltaic (PV) fast shutdown and arc sensing system, including: an AC power source, providing AC current; an arc sensing circuit, having an output portion indicating an arc; an AC injection transformer, for coupling the AC current to a DC bus of a photovoltaic panel array, the AC injection transformer having a first winding connected to the AC power source, a second winding connected to the DC bus, and a third winding connected to the arc sensing circuit and having turns in a direction opposite to the direction of the turns of the first winding; a shutdown control input portion, associated with one of the AC power source and the AC injector for interrupting the supply of AC current to the DC bus, the shutdown control input portion being connected to the output portion of the arc sensing circuit; and at least one isolation switch device, including: an AC coupler and a bandpass filter, connected in series between the input and output portions of the device; a rectifier gate signal circuit, connected to the AC coupler and providing a switch gate signal; and at least one normally open switch, connected in parallel with the bandpass filter, the gate of the at least one normally open switch being connected to the switch gate signal.

[0021] In another broad aspect, the present disclosure provides a method for detecting an arc in a photovoltaic system. The method includes: collecting a raw signal through a sensor connected to a DC bus of the photovoltaic system; applying a threshold local mean decomposition (LMD) to extract a first set of peaks and valleys from the raw signal; finding a first set of envelopes using the first set of peaks and valleys; applying a windowed local mean decomposition (LMD) to extract a second set of peaks and valleys from the raw signal; finding a second set of envelopes using the second set of peaks and valleys; comparing the first set of envelopes and the second set of envelopes; and sending an output signal indicating an arc when the first set of envelopes and the second set of envelopes simultaneously show an arc in the system. When the output signal indicates an arc, the current on the DC bus can be interrupted or the photovoltaic panel can be bypassed to eliminate the arc problem.

[0022] It should be understood that the sensor may be any type of sensor for detecting an arc, including sensors for detecting voltage and current on a DC bus.

[0023] In some examples of the method, sending an output indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously illustrate an arc in the system includes applying a blanking method to the first set of envelope curves and the second set of envelope curves.

[0024] In one example of the method, sending an output indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously illustrate an arc in the system includes applying a leaky bucket method to the first set of envelope curves and the second set of envelope curves.

[0025] In some examples, the method further includes applying mean subtraction to the first set of envelopes and the second set of envelopes.

[0026] In some examples of the method, the photovoltaic system is shut down when the output signal indicative of an electrical arc is sent.

[0027] In another broad aspect, the present disclosure provides an arc sensing circuit for use with a photovoltaic system, comprising: a sensor connected to a DC bus of the photovoltaic system to collect a raw signal from the DC bus; a control unit receiving the raw signal, the control unit comprising: a processor; and a non-transitory computer-readable medium containing instructions, which when executed by the processor causes the processor to perform: applying threshold local mean decomposition (LMD) to extract a first set of peaks and valleys from the raw signal; finding a first set of envelopes using the first set of peaks and valleys; applying windowed local mean decomposition (LMD) to extract a second set of peaks and valleys; finding a second set of envelopes using the second set of peaks and valleys; comparing the first set of envelopes and the second set of envelopes; and sending an output signal indicating an arc when the first set of envelopes and the second set of envelopes simultaneously show an arc in the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be better understood through the following detailed description of embodiments of the present invention with reference to the accompanying drawings, in which:

[0029] Figure 1 is a schematic diagram of a building equipped with rooftop photovoltaic panels, showing external remote shutoff control and optional arc sensing control at the combiner box, and internal inverters connected to the photovoltaic panels via a DC bus with disconnect switches at the photovoltaic panels;

[0030] Figure 2 yes Figure 1 A schematic block diagram of the electrical system involved; and

[0031] Figure 3 yes Figure 1 and Figure 2 Schematic diagram of the disconnector involved.

[0032] Figure 4 Shown are areas where an arc fault circuit interrupter should be able to detect or interrupt an arc based on the UL699 standard.

[0033] Figure 5 is a flow chart of steps included in a method for detecting an arc according to one embodiment of the present disclosure.

[0034] Figure 6 is a schematic diagram of a raw signal received by a processor for performing threshold LMD.

[0035] Figure 7 is found using the threshold LMD method according to one embodiment of the present disclosure Figure 6 Schematic diagram of the peaks and valleys of the original signal shown in .

[0036] Figure 8 are the peak and valley values ​​using the threshold LMD method according to one embodiment of the present disclosure ( Figure 7 Schematic diagram of the reconstructed signal (shown in ).

[0037] Fig. 9 is a threshold LMD method according to an embodiment of the present disclosure to find the reconstructed signal ( Figure 8 Schematic diagram of the envelope of ).

[0038] Fig.10 is the raw signal received by the processor for performing the threshold LMD (also in Figure 6 Schematic diagram of ).

[0039] Fig.11 is a schematic diagram of finding peak values ​​and valley values ​​within a sliding window at point 1 using the window LMD method according to an embodiment of the present disclosure.

[0040] Fig.12 is Fig.11 Schematic diagram of finding peaks and valleys within the sliding window when at point 2 as shown in .

[0041] Fig.13 is Fig.11 Schematic diagram of finding peaks and valleys within the sliding window when at point 3 as shown in FIG.

[0042] Fig.14 are the peak and valley values ​​using the window LMD method according to one embodiment of the present disclosure ( Fig.13 Schematic diagram of the reconstructed signal (shown in ).

[0043] Fig.15 is found using the window LMD method according to one embodiment of the present disclosure Fig.14 Schematic diagram of the envelope of the reconstructed signal in .

[0044] Fig.16A comparison and overlap of envelopes found using threshold LMD and window LMD are shown for jointly determining arc presence. DETAILED DESCRIPTION

[0045] Throughout the specification, "one embodiment", "an embodiment" or similar expressions mean that a particular feature, structure or characteristic described with respect to the embodiment is included in at least one embodiment of the present invention. Therefore, the appearances of "in one embodiment", "in an embodiment" and similar expressions throughout the specification may, but do not necessarily, all refer to the same embodiment.

[0046] In addition, the features, structures or characteristics described in the present invention may be combined in one or more embodiments in any suitable manner. It is apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the scope of the present invention. Therefore, the present invention is intended to encompass modifications and variations of the present invention, provided that they fall within the scope of the appended claims and their equivalents. Reference will now be made in detail to preferred embodiments of the present invention.

[0047] First introduced in the 2014 National Electrical Code (NEC), Rapid Shutdown is designed to provide firefighters with a simple way to easily deactivate the solar system’s DC conductors during a fire to ensure safe conditions on a building’s rooftop. This is because in a standard string inverter solar system, when the inverter is off, the solar system’s DC wiring remains live when the sun is shining.

[0048] In the 2017 NEC, rapid shutdown was expanded to include different requirements based on the proximity of the PV system conductors to the PV array boundary, which is now defined as the area extending 1 foot (305 mm) in all directions from the array.

[0049] PV circuits located outside the perimeter or more than 3 feet (1 meter) from a point of entry into a building should be limited to no more than 30 volts for 30 seconds after rapid shutdown is initiated.

[0050] For PV circuits located within the array boundary, one of the following three options must be used starting with the effective date of January 1, 2019:

[0051] PV arrays shall be listed or field labeled as Rapid Shutdown PV Arrays. Such PV arrays shall be installed and used in accordance with instructions that include Rapid Shutdown PV Array listing or field labeling. PV conductors located within the boundaries or no more than 3 feet (1 meter) from the point of penetration of the surface of the building shall be limited to no more than 80 volts for 30 seconds after rapid shutdown is initiated. PV arrays that have no exposed wiring methods, no exposed conductive parts, and are installed more than 8 feet from exposed grounded conductive parts or the ground are not required to comply with Rule 2 above.

[0052] In one example, the rapid shutdown system can be applied to a photovoltaic rooftop installation on a building, such as Figure 1 Schematically shown. In some configurations, the inverter 10 may be located within a building for converting DC power from a power bus 12 of photovoltaic panels 16. The photovoltaic panels 16 are mounted in a string configuration 18 on a rooftop exposed to sunlight. It should be understood that when DC storage of photovoltaic energy is desired, the unit 10 may include a battery charger.

[0053] In one embodiment of the present disclosure, a remote shutoff controller 20 is provided and, as shown, can be located on an exterior wall of a building. A combiner box 14 can be where the photovoltaic strings 18 are connected.

[0054] It should be understood that in some examples, initiation of the remote shutdown 20 may also be performed under the control of the inverter 10 . Figure 1 It is also schematically shown that the disconnector 30 is provided in the connection between the panels 16 as part of the power bus 12. The disconnector can be provided separately from the panel 16, or the disconnector can be integrated into the panel 16. Considering that the goal of the disconnector 30 is to keep the voltage on the DC bus 12 below a given threshold when shutdown is required, each panel 16 can be provided with one disconnector, or these disconnectors can be distributed in an array of panels 16.

[0055] like Figure 2 As shown, a rapid shutdown system 20, which may include an arc sense shutdown feature, may be built around a power source 24 and a plurality of isolation devices 30 (eg, one for each photovoltaic panel 16). The power source 24 may or may not be coupled through an AC injection transformer 26.

[0056] The AC injection transformer may have three windings. The first winding of the transformer may be part of a resonance tank that the power source 24 uses to generate the AC current. The second winding of the transformer may pass all of the photovoltaic DC current while injecting power on the DC line 12 of the array. A third winding, whose turns are in the opposite direction to the turns of the first winding, is connected to the arc sensing circuit 23. In this way, the injected AC signal will not be seen by the circuit 23, which will only see the noise that appears on the bus 12.

[0057] The arc sensing circuit is a circuit that is tuned to recognize signal characteristics caused by an arc and output a control signal to the controller 22 in response to those signal characteristics to initiate shutdown, such as by activating the disconnect switch 30 .

[0058] The power source 24 may have an operating frequency selected to optimize transmission across the photovoltaic array. From simulations and tests and literature review, the photovoltaic panel 16 appears to have a specific impedance. The disclosed system exploits the impedance of the photovoltaic and the quality factor of the photovoltaic to minimize the power loss injected on the photovoltaic cell. It has been noted from laboratory experiments that frequencies between 200kHz and 300kHz provide a high quality factor (low energy dissipation) and a linear (predictable) impedance while being below the AM band. It has been found that at 250kHz, only 20Vrms and 40mA of AC current are sufficient to supply all the isolation devices across a photovoltaic array with a cable length of 80 meters. Therefore, the experimental system demonstrated a power consumption of approximately 10mW per meter of cable length in the photovoltaic array (a power consumption of less than 20mW per meter of cable length in the photovoltaic array is expected). Using frequencies below 200kHz increases power consumption, and therefore it is best not to use frequencies below 100kHz. It is possible to use frequencies above 300kHz, but frequencies above 440kHz are not suitable due to being too close to the AM band of 540kHz.

[0059] like Figure 3As shown in , the isolation device 30 is built around a coil coupler or transformer 32 that picks up the supplied AC current on the DC bus 12 and supplies the gate of the switching device 36 using a rectifier circuit 34. Although the AC power provided to the bus 12 is extracted using the transformer coil 32, it should be understood that the required power can also be extracted using an equivalent capacitor coupling. Two normally open switches are shown in the drawings, and the use of two switches 36 provides redundancy in case one switch fails and also reduces the current load through each switch 36. It should be understood that more than two switches or a single switch 36 can be used. The bandpass filter 32 (e.g., an AC coupling capacitor) ensures that the AC current can always flow regardless of the state of the high voltage switch. The filter 38 can be tuned to allow the AC current to pass at a selected supply frequency, for example, between 200kHz and 300kHz. When the picked-up voltage is above a given threshold, it energizes the semiconductor switch 36, which will allow photovoltaic energy to flow to the load. Once the isolation device loses its supply, the rectifier circuit 34 stops supplying the gate signal and the switch 36 returns to the open state, rendering the photovoltaic array inoperable and the entire system safe to touch. The circuit 34 preferably contains capacitors and the time for the gate signal to open the switch 36 may be several seconds.

[0060] In some embodiments, the arc sensor may include an oscilloscope with a large memory, high sampling rate, and high bandwidth probe. The oscilloscope receives a real arc signal and uses local mean decomposition (LMD) and empirical mode decomposition (EMD) to detect arcs within the system. Arcs typically produce a wide spectrum, but the arc signal may also contain some harmonics of the natural resonant frequency of the system. Therefore, the method seeks to find a "beat" at the resonant frequency in order to detect the arc.

[0061] In some examples of the method, in order to detect the beat of the resonant frequency of the system, the original signal is passed through a threshold LMD and in parallel through a window LMD. The threshold LMD allows us to prevent false triggering of small noises that may be part of the harmonics associated with the natural resonant frequency of the system. In contrast, "large" noises will pass through this filter due to the nature of the arc, and large noises are part of the obvious features we want to detect. Window LMD prevents errors in detecting arcs by preventing the arc detection system from being triggered by very fast events, because typically fast transient events are not the beats we are looking for. After completing the window LMD, the filtered output signal is used to reconstruct the signal from the peaks found and find the envelope of the signal. After finding the two envelopes of the signal, they are compared, and if confirmed, we have detected an arc. The system then needs to be blanked and a leaky integrator is used to ensure that it does not trigger too quickly.

[0062] Figure 4 The areas where an arc fault circuit interrupter should be able to detect or interrupt an arc based on the UL699 standard are shown. As shown in the figure, area A: for all tests, interrupt the arc event in less than 2.5 seconds and limit the energy to no more than 200J; area B: for all tests, interrupt the arc event in less than 2.5 seconds and limit the energy to no more than 750J; and area C: for any test, the arc time is equal to or greater than 2.5 seconds, or the energy is greater than 750J, and the device is considered to be non-compliant with the standard.

[0063] Those skilled in the art will understand that, in this application, the envelope of a signal refers to the "profile" of the waveform; "Threshold LMD" is an LMD-based signal processing method that uses a predefined dead zone, hysteresis, or threshold to find the signal of interest; and "Window LMD" is an LMD-based signal processing method that uses a sliding window to find the signal of interest.

[0064] refer to Figure 5 , a flow chart of arc sensing using raw signals in a photovoltaic system is provided. S51 is receiving raw signals from a sensor connected to a DC bus of the photovoltaic system for collecting raw signals from the DC bus.

[0065] It should be understood that the sensor does not have to be connected and can be near the DC bus. For example, the sensor can benefit from electrical isolation but still provide a voltage or current signal. In S52, the method includes applying a threshold local mean decomposition (LMD) to extract a first set of peaks and valleys from the original signal. S54 includes finding the waveform envelope using the first set of peaks and valleys. In S56, the method may include applying mean subtraction to the signal. S53 includes applying a windowed local mean decomposition (LMD) to extract peaks and valleys from the signal, and then finding the envelope using these peaks and valleys in S55. In S57, the method may include applying mean subtraction to the envelope. Then in S60, the two envelopes found in steps S55 and S54 are compared, and if the envelopes simultaneously show that there is an arc in the system, the system can send an output signal indicating the arc. The method may also include applying blanking processing and / or leaky buckets in S62.

[0066] Figures 6 to 15 It shows that Figure 5 Schematic representation of the signals at each step of the process described. Figure 6 is a schematic diagram of the raw signal received by the processor from our sensor. Figure 7 The use of a threshold LMD method to find the peaks and valleys of a signal received from a sensor is shown. Figure 8 shows the use of threshold LMD as performed Figure 7 The peaks and valleys shown in the reconstructed signal. Fig. 9 In , the reconstructed signal is used to find the envelope (the outline of the waveform).

[0067] Fig.10 It is a schematic diagram of the original signal received by the window LMD. Figures 11 to 13 Finding the peak and valley within the sliding window at points 1 to 2 as performed in the windowed LMD method is shown. Fig.14 is a schematic diagram of reconstructing the signal using peaks and valleys as done in the windowed LMD method, and then Fig.15 Finally, Fig.16 A comparison and overlap of the envelopes found using threshold LMD and window LMD is shown, during which a consistent determination of arc presence allows the conclusion that arcing is occurring.

Claims

1. A disconnect switch device for a photovoltaic (PV) panel, the device comprising: an AC coupler and a bandpass filter connected in series between the input and output of the device; A rectifier gate signal circuit connected to the AC coupler and providing a switch gate signal; as well as At least one normally open switch is connected in parallel with the bandpass filter, and a gate of the at least one normally open switch is connected to the switch gate signal.

2. The apparatus of claim 1, wherein the bandpass filter is operative to pass AC signals in the range of 200 kHz to 300 kHz.

3. The device according to claim 1 or 2, wherein the AC coupler is a transformer.

4. The apparatus of any one of claims 1 to 3, wherein the at least one normally-open switch comprises a pair of normally-open switches connected in parallel with a bandpass filter.

5. A photovoltaic (PV) rapid shutdown system comprising: AC power supply, providing AC current; an AC injector for coupling said AC current to a DC bus of a photovoltaic panel array; a shutdown control input associated with one of the AC power source and the AC injector for interrupting the supply of the AC current to the DC bus; as well as At least one disconnect switch device according to any one of claims 1 to 4 can be connected to the DC bus.

6. A photovoltaic (PV) rapid shutdown and arc sensing system comprising: AC power supply, providing AC current; an arc sensing circuit having an output portion for indicating an arc; an AC injection transformer for coupling the AC current to a DC bus of a photovoltaic panel array, the AC injection transformer having a first winding connected to the AC power source, a second winding connected to the DC bus, and a third winding connected to the arc sensing circuit and having turns in a direction opposite to that of the first winding; a shutoff control input associated with one of the AC power source and the AC injector for interrupting the supply of the AC current to the DC bus, the shutoff control input being connected to the output of the arc sensing circuit; as well as At least one disconnect switch device according to any one of claims 1 to 4.

7. The apparatus of claim 6, wherein the arc sensing circuit comprises: - a sensor connected to the DC bus of the photovoltaic system to collect raw signals from the DC bus; - a control unit, receiving the original signal, the control unit comprising: - processor; and - a non-transitory computer-readable medium comprising instructions which, when executed by the processor, cause the processor to: - applying thresholded local mean decomposition (LMD) to extract a first set of peaks and valleys from the original signal; - finding a first set of envelope curves using said first set of peaks and valleys; - Apply windowed local mean decomposition (LMD) to extract a second set of peaks and valleys; - finding a second set of envelopes using said second set of peaks and valleys; - comparing said first set of envelopes with said second set of envelopes; - sending an output signal indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously show an arc in the system.

8. The system of claim 5, 6 or 7, further comprising the photovoltaic panel array connected to the DC bus, the AC power source providing less than 20 mW per meter of power to the DC bus in the photovoltaic panel array.

9. A method for providing emergency power off of a photovoltaic panel, the method comprising: - Injecting AC current on the DC bus of the photovoltaic panel array; - isolating the AC current from the DC bus; as well as - Using isolated said AC current resulting in a passive circuit allows DC current to flow from the photovoltaic panel through said DC bus, wherein interruption of said AC current provides emergency de-energization of said DC bus.

10. The method of claim 9, wherein using the isolated AC current to cause a passive circuit to allow DC current to flow from a photovoltaic panel through the DC bus comprises: - receiving the isolated AC current through a rectifier gate signal circuit providing a switch gate signal; as well as - using the switch gate signal to close at least one normally open switch to allow DC current to flow from the photovoltaic panel through the DC bus; When the AC current is interrupted, the at least one normally open switch is disconnected and stops the DC current from flowing through the DC bus.

11. The method of claim 10, wherein isolating the AC current from the DC bus comprises isolating the AC current using a transformer.

12. The method of any one of claims 9 to 11, wherein injecting an alternating current on a DC bus of a photovoltaic panel array comprises injecting the alternating current at a frequency different from an operating frequency of an inverter receiving the DC voltage.

13. The method according to any one of claims 9 to 12, further comprising: collecting raw signals from the DC bus; applying thresholded local mean decomposition (LMD) to extract a first set of peaks and valleys from the original signal; finding a first set of envelope curves using the first set of peaks and valleys; Apply windowed local mean decomposition (LMD) to extract the second set of peaks and valleys; finding a second set of envelopes using the second set of peaks and valleys; comparing the first set of envelopes with the second set of envelopes; The AC current on the DC bus is removed when the comparison of the first set of envelopes and the second set of envelopes simultaneously shows an arc.

14. The method of claim 13, further comprising applying a blanking method to the first set of envelope curves and the second set of envelope curves.

15. The method of claim 13, further comprising applying a leaky bucket method to the first set of envelopes and the second set of envelopes.

16. The method of any one of claims 13 to 15, further comprising applying a mean subtraction method to the first set of envelope curves and the second set of envelope curves.

17. A method for arc detection in a photovoltaic system, the method comprising: - Collecting raw signals through sensors connected to the DC bus of the photovoltaic system; - applying thresholded local mean decomposition (LMD) to extract a first set of peaks and valleys from the original signal; - finding a first set of envelope curves using said first set of peaks and valleys; - Apply windowed local mean decomposition (LMD) to extract a second set of peaks and valleys; - finding a second set of envelopes using said second set of peaks and valleys; - comparing said first set of envelopes with said second set of envelopes; - sending an output signal indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously show an arc in the system.

18. The method of claim 17, wherein sending an output indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously illustrate an arc in the system comprises applying a blanking method to the first set of envelope curves and the second set of envelope curves.

19. The method of claim 17, wherein sending an output indicative of an arc when the first set of envelopes and the second set of envelopes simultaneously illustrate an arc in the system comprises applying a leaky bucket method to the first set of envelopes and the second set of envelopes.

20. The method of any one of claims 17 to 19, further comprising applying a mean subtraction method to the first set of envelope curves and the second set of envelope curves.

21. The method of any one of claims 17 to 20, further comprising shutting down the photovoltaic system when sending an output signal indicative of an electrical arc.

22. An arc sensing circuit for use with a photovoltaic system, comprising: - a sensor connected to a DC bus of the photovoltaic system to collect a raw signal from the DC bus; - a control unit, receiving the original signal, the control unit comprising: - processor; and - a non-transitory computer-readable medium comprising instructions which, when executed by the processor, cause the processor to perform: - applying thresholded local mean decomposition (LMD) to extract a first set of peaks and valleys from the original signal; - finding a first set of envelope curves using said first set of peaks and valleys; - Apply windowed local mean decomposition (LMD) to extract a second set of peaks and valleys; - finding a second set of envelopes using said second set of peaks and valleys; - comparing said first set of envelopes with said second set of envelopes; - sending an output signal indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously show an arc in the system.

23. The arc sensing circuit of claim 22, wherein the non-transitory computer readable medium further comprises instructions that, when executed by the processor, cause the processor to perform: Sending an output indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously illustrate an arc in the system includes applying a blanking method to the first set of envelope curves and the second set of envelope curves.

24. The arc sensing circuit of claim 22, wherein the non-transitory computer readable medium further comprises instructions that, when executed by the processor, cause the processor to perform: Wherein sending an output indicative of an arc when the first set of envelope curves and the second set of envelope curves simultaneously illustrate an arc in the system comprises applying a leaky bucket method to the first set of envelope curves and the second set of envelope curves.

25. The arc sensing circuit of any one of claims 22 to 24, wherein the non-transitory computer readable medium further comprises instructions that, when executed by the processor, cause the processor to further perform: A mean subtraction method is applied to the first set of envelope curves and the second set of envelope curves.

26. The arc sensing circuit of any one of claims 22 to 25, wherein the non-transitory computer readable medium further comprises instructions that, when executed by the processor, cause the processor to further perform: The photovoltaic system is shut down when the output signal indicative of an electrical arc is sent.

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