Claims:
1. A method for insulation/ground fault detection for a photo voltaic (PV) array, the method comprising:
determining resistance of each PV string of the PV array;
determining a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array;
comparing each value of the set of resistance difference values with a pre-set first value; and
generating a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
2. A system for insulation/ground fault detection for a photo voltaic (PV) array, said system comprising a controller, characterized in that said controller is configured to:
determine resistance of each PV string of the PV array;
determine a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array;
Compare each value of the set of resistance difference values with a pre-set first value; and
generate a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
3. The system of claim 2, wherein the controller comprises a voltage divider network, an amplifier, a comparator and a fault signal generator.
4. The system of claim 2, wherein the fault signal is used for any or a combination of generating an alarm, shutting down an inverter operated by the PV array and isolating the photovoltaic array completely from rest of the system.
, Description:
FIELD OF DISCLOSURE

[0001] The present disclosure relates to Photo Voltaic Systems. In particular, it pertains to systems to avoid hazards and increase safety in such systems.

BACKGROUND OF THE DISCLOSURE

[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] An insulation fault that in turn leads to a ground fault is one of the most common in Photo Voltaic (PV) systems. A ground fault is "the undesirable condition of current flowing through the grounding conductor." The cause of this undesirable current flow is an unintentional electrical connection between a current-carrying conductor in the PV system and the equipment grounding conductor (EGC). This could be because of insulation failure.
[0004] Ground faults are not only some of the most aggravating and labor intensive situations encountered in PV installations; they can also be downright dangerous. While both the National Electrical Code (NEC) and UL require that grid-tied photovoltaic inverters shut down in the event of a ground fault, shutting down the inverter does not normally clear the fault. This can create a number of hazards since the normally grounded current-carrying conductor may no longer be at ground potential. In addition, if the grounding system is inadequate, module frames, metal structures or enclosures may be energized and can present a shock hazard to personnel. Electricians, installers or service technicians troubleshooting a ground fault need to proceed as if everything conductive is at lethal potential to ground—until a multi-meter proves otherwise—lest they become the inadvertent ground path for that fault current.
[0005] NEC Article 690.5 specifies the ground-fault protection requirements for grounded DC photovoltaic arrays. Ground fault protection is also required for ungrounded PV systems; these requirements are detailed in 690.35(C). The specified purpose of a ground-fault protection device (GFPD) as part of a PV power system is to reduce the risk of fire associated with a ground fault. If the ground fault is a short-circuit the fault current can be very high. In addition to being a safety hazard, this creates a significant fire hazard as bare metal is heated by the current flow.
[0006] Because of this fire hazard, ground-fault protection for PV array circuits was first required for roof-mounted residential PV installations, where the perceived risk of fire is great. The potential for property damage or loss of life when a PV system is installed on the roof of a home, for example, is greater than it is where a PV system is ground-mounted in a field at some distance from a building.
[0007] Nevertheless, as the fire hazards associated with PV systems have become increasingly understood and documented, the GFPD requirements outlined in the Code have become more inclusive. Ground-fault protection is not just for residential roofs anymore. The 2008 NEC, for example, requires ground-fault protection for all “grounded dc photovoltaic arrays.” The seminal event that prompted this recent change was a ground fault that melted through the side of metal conduit on a medium sized commercial system.
[0008] Ground faults are typically caused by damage in the protective insulation of normally current-carrying conductors. The copper material may then contact and energize metallic equipment, such as enclosures, conduit, structures, and bare grounding conductors. The potential causes of damage to current-carrying conductor insulation are many. Pulling wire through conduit may result in chafed or damaged insulation. This is especially true if there are sharp metal edges caused by a lack of conduit bushings or metal shavings in the conduit. Anywhere those current-carrying conductors are exposed to abrasion, there is a possibility of a ground fault. Other potential causes of ground faults include: PV source-circuit conductors pinched between module frames and mounting structures, conductors rubbing against the roof, varmints chewing on conductors, broken PV modules, incorrect wiring of PV modules and internal faults in inverters or charge controllers.
[0009] The most frustrating ground faults are intermittent. These might show up after a major rain or wind event, for example. Water, of course, can become a conductor, and in some cases it can electrically bond a current-carrying conductor to ground. When the water evaporates, so does the ground fault. Another potential cause of intermittent faults is normal temperature-related expansion or contraction of metals—the ground fault might occur only during extreme hot or cold ambient conditions. In some cases, intermittent ground faults disappear as fast as they shut the PV system down. This can be true where arcing and the resultant carbon buildup occur. Because an intermittent ground fault may not be present when troubleshooting occurs, pinpointing the problem is extremely difficult.
[00010] Patent US 8773156 B2 “Measurement of insulation resistance of configurable photovoltaic panels in a photovoltaic array” measures insulation resistance in a PV array by partitioning the array into groups of PV panels, determine insulation resistance of each group and on finding an insulation problem on any group using bypass selectors provided on each panel to further isolate the defective panel. The system is complex to configure and operate since resistance of each panel needs to be measured, and does not allow for fault detection to be performed online.
[00011] Patent Number US 20130285670 A1 titled “Ground fault detection device, ground fault detection method, solar energy generator system, and ground fault detection program” elaborates upon a ground fault detection device that is used in a photovoltaic array composed of plurality of photovoltaic strings connected in parallel. The device includes a switching section that parallels off the photovoltaic array or the photovoltaic string by electrically disconnecting the photovoltaic array or the photovoltaic string from the solar energy generator system and a detection section that detects a ground fault in the photovoltaic array or the photovoltaic string while the photovoltaic array or the photovoltaic string is paralleled off by the switching section. Since the system requires electrically disconnecting the photovoltaic array, it is complex to configure and operate, and does not allow for fault detection to be performed online.
[00012] Patent Number US 9103865 B2 titled “Methods for locating ground faults and insulation degradation condition in energy conversion systems” elaborates upon a method of detecting a ground fault within an energy conversion system, the method relying upon obtaining a baseline frequency spectra of differential current for the plurality of DC carrying conductors included in the energy conversion system and comparing same to the frequency spectra of the measured current during operation; and determining whether a ground fault exists based upon such comparison. A ground fault within a current carrying conductor may be detected and located by measuring the values of DC network transient current within the energy conversion system and analyzing the time domain waveforms and/or frequency spectra. The system relies upon comparing frequency spectra and hence is complex to configure and operate.
[00013] Hence there is a need in the art for a system that is simple, inexpensive, and can continuously monitor an array of a photo voltaic system to detect an insulation/ground fault therein as soon as it happens and take immediate corrective actions to avoid hazards as elaborated above to life and property.
[00014] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[00015] In some embodiments, the numbers expressing quantities or dimensions of items, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[00016] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00017] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00018] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION

[00019] Some of the objects of the present disclosure, which at least one embodiment herein satisfies are as listed herein below.
[00020] It is an object of the present disclosure to provide for a system for insulation/ground fault detection and monitoring for a photo voltaic panel array that detects such faults online.
[00021] It is another object of the present disclosure to provide for a system as above that is simple to operate and uses less components.
[00022] It is another object of the present disclosure to provide for a system as above that can identify faults occurring due to insulation failure of the cables, incidental short circuit between normal conductor and ground and also ground fault within an individual PV panel as well.

SUMMARY OF THE INVENTION

[00023] In an aspect, present disclosure proposes a method for insulation/ground fault detection for a photo voltaic (PV) array, the method including determining resistance of each PV string of the PV array; determining a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array; comparing each value of the set of resistance difference values with a pre-set first value; and generating a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
[00024] In another aspect, present disclosure proposes a system for insulation/ground fault detection for a photo voltaic (PV) array, said system including a controller, characterized in that said controller is configured to determine resistance of each PV string of the PV array; determine a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array; compare each value of the set of resistance difference values with a pre-set first value; and generate a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
[00025] In yet another aspect, the controller of the proposed system can include a voltage divider network, an amplifier, a comparator and a fault signal generator.
[00026] In yet another aspect, the fault signal can be used for any or a combination of generating an alarm, shutting down an inverter operated by the PV array and isolating the photovoltaic array completely from rest of the system.
[00027] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.

BRIEF DESCRIPTION OF DRAWINGS

[00028] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:
[00029] FIG. 1 illustrates an overall block diagram of a photovoltaic power generation system being used along with proposed system, in accordance with an exemplary embodiment of the present disclosure.
[00030] FIG. 2 illustrates a method of working of system proposed, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[00031] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[00032] In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without some of these specific details.
[00033] Embodiments of the present invention include various steps, which will be described below. The steps may be performed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor programmed with the instructions to perform the steps. Alternatively, steps may be performed by a combination of hardware, software, and firmware and/or by human operators.
[00034] Various methods described herein may be practiced by combining one or more machine-readable storage media containing the code according to the present invention with appropriate standard computer hardware to execute the code contained therein. An apparatus for practicing various embodiments of the present invention may involve one or more computers (or one or more processors within a single computer) and storage systems containing or having network access to computer program(s) coded in accordance with various methods described herein, and the method steps of the invention could be accomplished by modules, routines, subroutines, or subparts of a computer program product.
[00035] If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[00036] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[00037] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.
[00038] Thus, for example, it will be appreciated by those of ordinary skill in the art that the diagrams, schematics, illustrations, and the like represent conceptual views or processes illustrating systems and methods embodying this invention. The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing associated software. Similarly, any switches shown in the figures are conceptual only. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the entity implementing this invention. Those of ordinary skill in the art further understand that the exemplary hardware, software, processes, methods, and/or operating systems described herein are for illustrative purposes and, thus, are not intended to be limited to any particular named element.
[00039] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[00040] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[00041] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[00042] In an aspect, present disclosure proposes a method for insulation/ground fault detection for a photo voltaic (PV) array, the method including determining resistance of each PV string of the PV array; determining a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array; comparing each value of the set of resistance difference values with a pre-set first value; and generating a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
[00043] In another aspect, present disclosure proposes a system for insulation/ground fault detection for a photo voltaic (PV) array, said system including a controller, characterized in that said controller is configured to determine resistance of each PV string of the PV array; determine a set of resistance difference values, wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array; compare each value of the set of resistance difference values with a pre-set first value; and generate a fault signal if at least one value of the set of resistance difference values is higher than the pre-set first value.
[00044] In yet another aspect, the controller of the proposed system can include a voltage divider network, an amplifier, a comparator and a fault signal generator.
[00045] In yet another aspect, the fault signal can be used for any or a combination of generating an alarm, shutting down an inverter operated by the PV array and isolating the photovoltaic array completely from rest of the system.
[00046] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.
[00047] FIG. 1 illustrates an overall block diagram of a photovoltaic power generation system being used along with proposed system, in accordance with an exemplary embodiment of the present disclosure.
[00048] In an aspect proposed system can determine resistance of each PV string of the PV array.
[00049] In another aspect, proposed system can determine a set of resistance difference values wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array.
[00050] It can be readily appreciated that if a ground/insulation fault develops in any string of the PV array, its resistance shall fall. Hence difference of resistance of this PV string with the rest of PV strings of the PV array shall go up. This increase can be used to generate a fault signal as elaborated hereunder.
[00051] In yet another aspect, proposed system can compare each value of the set of resistance difference values with a pre-set first value and can generate a fault signal if any of the values of set of resistance difference values is higher than the pre-set first value.
[00052] In this fashion, proposed system can continuously monitor each string for continuous and online determination of the difference in resistance amongst all strings of the PV array and can generate a fault signal if any of the values of set of resistance difference values is more than the pre-set first value.
[00053] In an aspect, the fault signal can be used for various other tasks such as generating an alarm and shutting down the grid-tied photovoltaic inverter, isolating the photovoltaic array completely from rest of the system etc. in order to avoid any hazard to personnel and property such as electric shocks, fire etc.
[00054] In an exemplary embodiment as illustrated, proposed system can include a voltage divider network 118, an amplifier 102, a comparator 104 and a fault signal generator 106.
[00055] In another aspect, the power generation system for use with proposed system can comprise a PV array of a plurality of strings of PV (photo voltaic) panels connected in parallel to each other to deliver required voltage. In an exemplary embodiment as shown, such strings can be illustrated as 108a and 108b.
[00056] In yet another aspect, each string can have required number of PV panels connected in series. In exemplary embodiment as shown, each string can have eight PV panels shown as 110-1, 110-2.110-8 for string 108a (and likewise 112-1, 112-2..112-8 for string 108b) that are connected in series.
[00057] In an aspect, voltage developed by the PV array can be delivered via switches S1 (114) and S2 (116) to the voltage divider network 118.
[00058] As can be appreciated, voltage being delivered to the voltage divider network 118 depends upon resistances of string 108a and 108b. If these resistances vary due to any reason such as an insulation fault or a ground fault at any place in the strings, voltage delivered to the voltage divider network 118 will vary. Proposed system can use the voltage and the variances therein to determine resistances in strings of the photovoltaic array and changes therein.
[00059] In yet another exemplary embodiment, proposed system can determine a resistance difference value between string 108a and string 108b and can pass the resistance difference value using the voltage divider network 118 to amplifier 102.
[00060] In an exemplary embodiment, amplifier 102 can amplify the resistance difference value and transmit the amplified resistance difference value to comparator 104. The comparator 104 can compare this amplified resistance difference value with a pre-set value. In case the amplified resistance difference value is higher than a pre-set value, comparator 104 can pass the amplified resistance difference value to fault signal generator 106.
[00061] In another exemplary embodiment, upon receiving the amplified resistance difference value, fault signal generator 106 can generate a fault signal that can in turn be used for various purposes such as raising an alarm and interrupting the power being generated by the photovoltaic power generation system. In case power being generated is being supplied to an inverter, the fault signal can stop the inverter as well.
[00062] To generate different voltages from the PV array as well as for various operations of voltage divider network 118, different resistances can be connected before/after different PV panels and at negative or positive terminals of the PV array. Besides, switches 114 and 116 can remain ON or OFF as required. Using simulation techniques, the pre-set value for such different conditions can be determined and set when the PV array is operating under corresponding condition to provide appropriate insulation/ground fault detection and further actions as elaborated above.
[00063] As can be appreciated, resistance difference values can be expressed as a percentage as well, to create a set of normalized resistance difference values to account for different settings of PV array and /or voltage divider network.
[00064] Since the proposed system relies upon difference in resistance values of identical PV strings, it can readily be understood it can identify faults occurring due to insulation failure of the cables, incidental short circuit between normal conductor and ground and also ground fault within an individual PV panel as well.
[00065] FIG. 2 illustrates a method of working of system proposed, in accordance with an exemplary embodiment of the present disclosure.
[00066] In an aspect the method can include, at step 202, determining resistance of each PV string of a PV array.
[00067] In another aspect the method can include, at step 204, determining a set of resistance difference values wherein the set comprises difference of resistance of each PV string of the PV array with rest of PV strings of the PV array.
[00068] In yet another aspect the method can include, at step 206, comparing each value of the set of resistance difference values with a pre-set first value.
[00069] In an aspect, the method can include, at step 208, determining if at least one value of the set of resistance difference values is higher than the pre-set first value and proceeding again from step 202 if no value of set of resistance difference values is higher than the pre-set first value.
[00070] In an aspect, the method can include, at step 210, generating a fault signal if at least one value of set of resistance difference values is higher than the pre-set first value.
[00071] Although the proposed system has been elaborated as above to include all the main modules, it is completely possible that actual implementations may include only a part of the proposed modules or a combination of those or a division of those into sub-modules in various combinations across multiple devices that can be operatively coupled with each other, including in the cloud. Further the modules can be configured in any sequence to achieve objectives elaborated. All such modifications and embodiments are completely within the scope of the present disclosure.
[00072] As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other or in contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. Within the context of this document terms “coupled to” and “coupled with” are also used euphemistically to mean “communicatively coupled with” over a network, where two or more devices are able to exchange data with each other over the network, possibly via one or more intermediary device.
[00073] Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
[00074] While some embodiments of the present disclosure have been illustrated and described, those are completely exemplary in nature. The disclosure is not limited to the embodiments as elaborated herein only and it would be apparent to those skilled in the art that numerous modifications besides those already described are possible without departing from the inventive concepts herein. All such modifications, changes, variations, substitutions, and equivalents are completely within the scope of the present disclosure. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.

ADVANTAGES OF THE INVENTION

[00075] The present disclosure provides for a system for insulation/ground fault detection and monitoring for a photo voltaic panel array that detects such faults online.
[00076] The present disclosure provides for a system as above that is simple to operate and uses less components.
[00077] The present disclosure provides for a system as above that can identify faults occurring due to insulation failure of the cables, incidental short circuit between normal conductor and ground and also ground fault within an individual PV panel as well.