Abstract:
Embodiments of apparatuses, systems, articles, and methods related to a photovoltaic module monitoring system are disclosed. Other embodiments may be described and claimed.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Provisional Application No. 61/103,366 filed on Oct. 7, 2008, which is hereby incorporated by reference in its entirety for all purposes except for those sections, if any, that are inconsistent with the present application. 
     
    
     BACKGROUND 
       [0002]    Recent years have seen a significant increase in both the number and scale of photovoltaic (PV) installations. Installing and maintaining PV modules of a PV installation may be associated with a number of challenges at both residential and commercial scales. Some typical challenges that may be encountered during a commissioning of a PV installation include incorrect and/or faulty wiring resulting in, e.g., incorrect polarity, open wiring, ground faults, loss of panel ground wire integrity, etc. Some typical challenges that may be encountered during operation of a PV installation include open wiring, resistive wiring, and ground faults. Occurrence of any of these situations could be detrimental to the electrical generation capacities of the PV installation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
           [0004]      FIG. 1  is a block diagram of a photovoltaic installation; 
           [0005]      FIG. 2  is a block diagram of a managed module; 
           [0006]      FIG. 3  is a block diagram of portions of a managed module; 
           [0007]      FIG. 4  is a block diagram of a string combiner; 
           [0008]      FIG. 5  is a block diagram of a string management unit; 
           [0009]      FIG. 6  is a flow diagram of operations within a mapping procedure; 
           [0010]      FIG. 7  is a flow diagram of operations within a procedure for detecting a ground fault; 
           [0011]      FIG. 8  is a flow diagram of operations within another procedure for detecting a ground fault; 
           [0012]      FIG. 9  is a flow diagram of operations within another procedure for detecting a ground fault; 
           [0013]      FIG. 10  is a flow diagram of operations within a procedure for determining a location of a ground fault; 
           [0014]      FIG. 11  is a flow diagram of operations within a procedure for detecting an open wire; and 
           [0015]      FIG. 12  is a flow diagram of operations within a procedure for detecting a weak wire, all in accordance with some embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific devices and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. 
         [0017]    Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present disclosure; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. 
         [0018]    The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. 
         [0019]    In providing some clarifying context to language that may be used in connection with various embodiments, the phrases “A/B” and “A and/or B” mean (A), (B), or (A and B); and the phrase “A, B, and/or C” means (A), (B), (C), (A and B), (A and C), (B and C) or (A, B and C). 
         [0020]    The term “coupled with,” along with its derivatives, may be used herein. “Coupled” may mean one or more of the following. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements indirectly contact each other, but yet still cooperate or interact with each other, and may mean that one or more other elements are coupled or connected between the elements that are said to be coupled to each other. The term “electrically coupled” means that two or more elements are in electrical communication with one another. The term “communicatively coupled” means that two or more elements are capable of communicating with one another. This communication may be done through a wired connection, a wireless connection, a network, etc. 
         [0021]    Embodiments of this disclosure provide for systems, apparatuses, and methods to allow rapid and accurate detection of abnormalities that may exist in a photovoltaic (PV) installation. These abnormalities may result from installation errors and/or events that occur during operation of the PV installation. Embodiments also provide for continuous performance monitoring of PV modules in a PV installation during operation. 
         [0022]      FIG. 1  is a block diagram of a PV installation  100  in accordance with some embodiments. The PV installation  100  may have a string combiner (SC)  104  electrically coupled with a central inverter  108  through a conduit  112 ; communicatively coupled with an array link gateway (ALG)  116 ; and electrically coupled with a number of PV modules  124 , e.g., PV modules  124 - 1 - 124 - 6 . The ALG  116  may operate to communicatively couple the PV installation  100  to a central management/monitoring facility over a network. The central inverter  108  may include a ground fault detection interrupt (GFDI)  126 , to disconnect the PV installation when a ground fault is detected at the central inverter  108 , and a ground integrity test source (GITS)  130 , to test the integrity of a ground. 
         [0023]    The PV installation  100  may also include a number of active module sensors (AMSs)  128 , e.g., AMSs  128 - 1 - 128 - 6 , with each of the AMSs  128  electrically coupled with a corresponding PV module  124  as generally shown in  FIG. 1 . In some embodiments, the AMS  128  may be a component that is external to its corresponding PV module  124 , as is generally shown in  FIG. 1 . In other embodiments, the AMS  128 , or components thereof, may be integrated into its corresponding PV module  124 . A PV module  124  and its corresponding AMS  128  may be collectively referred to as a managed module  132 . 
         [0024]    As used herein, PV module  124  and PV modules  124  may respectively refer to a generic PV module and to more than one PV modules (up to all of the PV modules) depending on the context in which it is used. Also, use of a common portion of a reference number may indicate similar types of components; however, it does not imply that the components must be identical with one another. For example, PV module  124 - 1  may, or may not, be identical with PV module  124 - 2 . These interpretations may also apply to other references used in a similar manner. 
         [0025]    In addition to being electrically coupled with a PV module  124 , the AMSs  128  may also be communicatively coupled with the SC  104 . This may enable the AMSs  128  to communicate with the SC  104  to manage the PV modules  124  as will be described. 
         [0026]    The SC  104  may include a string management unit (SMU)  136  coupled with each string  140  of PV modules  124 . An SMU  136 - 1  may be coupled with a string  140 - 1  that includes managed modules  132 - 1 - 132 - 3 ; and an SMU  136 - 2  may be coupled with a string  140 - 2  that includes managed modules  132 - 4 - 132 - 6 . In particular, the SMU  136 - 1  may be coupled with a positive string interconnect  144 - 1  and a negative string interconnect  148 - 1 ; and SMU  136 - 2  may be coupled with a positive string interconnect  144 - 2  and a negative string interconnect  148 - 2 . The SC  104  may also include an SMU controller  152 . 
         [0027]    In some embodiments, such as the one shown in  FIG. 1 , there will be one AMS  128  per PV module  124 ; one SMU  136  per string  140 ; one SMU controller  152  per SC  104 ; and/or one ALG  116  per central inverter  108 . 
         [0028]      FIGS. 2-5  briefly introduce components of the managed module  132  ( FIG. 2 ), the PV module  124  and a linear pre-regulator ( FIG. 3 ), the SC  104  ( FIG. 4 ), and the SMU  136  ( FIG. 5 ) in accordance with some embodiments. These components may be discussed in further detail with respect to the procedures described in detail in  FIGS. 6-12  in accordance with some embodiments. 
         [0029]      FIG. 2  is a block diagram of a managed module  132  with additional details of an AMS  128  in accordance with some embodiments. The AMS  128  may include a voltage regulator (VR)  204  coupled with a positive interconnect  208  and a negative interconnect  212 . As used herein, “interconnect” or “line” may include any type of conductor that may be used to electrically couple two components. This may include, but is not limited to, a wire, a trace, a conductive plane, etc. 
         [0030]    The VR  204  may generate a controlled (e.g., substantially constant) voltage having characteristics desired for operation of other components of the AMS  128 . The VR  204  may be a hybrid regulator with a linear pre-regulator followed by a switching regulator. The linear pre-regulator may step down the voltage of the positive interconnect  208  and the negative interconnect  212  to a voltage that is acceptable to the switching regulator. 
         [0031]      FIG. 3  is a block diagram of portions of the managed module  132  including a linear pre-regulator  304  in accordance with some embodiments. The linear pre-regulator  304  may be placed between PV sections  308  and a switching regulator  306 . The linear pre-regulator  304  may have three bypass diodes  312  respectively coupled, in parallel, with three PV sections  308  on section line  310  as shown. PV section  308 - 1  may be electrically coupled with M−, a negative terminal of the PV module  124 , and PV section  308 - 3  may be electrically coupled with M+, a positive terminal of the PV module  124 . In addition to being electrically coupled with M+ and M−, the linear pre-regulator  304  may be electrically coupled with the section line  310  at points between adjacent PV sections  308 . 
         [0032]    The linear pre-regulator  304  may also have a number of transistors, e.g., transistors  316 - 1 - 316 - 5 , which may be NMOS transistors; a number of diodes, e.g., diodes  320 - 1 - 320 - 3 ; a number of resistors, e.g., resistors  324 - 1 - 324 - 5 ; and a number of additional diodes, e.g., Zener diodes  328 - 1 - 328 - 4 , coupled to one another as shown. While the resistors  324  are shown with respective sizes of a particular embodiment, they may be other sizes in other embodiments. 
         [0033]    In normal operation, transistors  316 - 2  and  316 - 3  may be turned off due to transistors  316 - 4  and  316 - 5  being turned on. When PV section  308 - 1  is bypassed due to, e.g., shading or a fault in bypass diode  312 - 1 , transistor  316 - 2  may turn on to supply power to the switching regulator  306 . Transistor  316 - 3  may be turned on when both bypass diodes  312 - 2  and  312 - 3  are bypassed due to e.g., shading or fault in bypass diodes  312 - 2  and/or  312 - 3 . 
         [0034]    Tapping the linear pre-regulator  304  into the section line  310  between adjacent PV sections  308 , as shown, allows the use of smaller and lower cost components in the linear pre-regulator  304 . This configuration may be desired in embodiments in which at least portions of the AMS  128  are incorporated into the PV module  124 , as direct access to the section line  310  at points between adjacent PV sections  308  may not be available in embodiments in which the AMS  128  is externally coupled to a PV module  124  as may occur in, e.g., a retrofit deployment. The benefits of this configuration may be realized when the PV modules  124  are crystalline or high-voltage thin-film modules. 
         [0035]    Referring again to  FIG. 2 , the AMS  128  may also include a transient voltage suppressor (TVS)  216  coupled with the positive interconnect  208  and the negative interconnect  212 . The TVS  216  may protect electronics of the AMS  128  from transient overvoltage conditions that may result from nearby lightning strikes and other electrical disturbances. The TVS  216  may include, but is not limited to, a diode or a metal oxide varistor. 
         [0036]    The AMS  128  may also include a current sensor (CS)  220  configured to measure current associated with the PV module  124 . The current sensor  220  may be coupled with the negative interconnect  212  to facilitate implementation, e.g., by using smaller components. The current sensor  220  and the positive interconnect  208  may be coupled with a buffer/filter  224  that is configured to remove voltage transients and noise from voltage and current measurement prior to sampling by analog-to-digital circuit (ADC)  228 . The ADC  228  may be coupled with a controller  232 . The controller  232  may be coupled with memory/storage  236  and a wireless transceiver  240 . The wireless transceiver  240  may be configured to communicatively couple the AMS  128  with the SC  104  via an over-the-air link. The wireless transceiver  240  may send various measurements (e.g., current and/or voltage measurements) to the SC  104  and/or receive various command messages from the SC  104 . In some embodiments, the wireless transceiver  240  may be configured to operate in an Industrial, Scientific, and Medical (ISM) radio band; however, other embodiments are not so limited. 
         [0037]    A “controller,” as used here and elsewhere, may be a processing component capable of controlling components coupled thereto in a manner to provide the described result. In some embodiments, the controller may be a microcontroller, a microprocessor, a system-on-a-chip, etc. 
         [0038]    The AMS  128  may also include a voltage limiter (VL)  244  coupled with the positive interconnect  208  and a ground wire integrity check (GWIC) relay  248 , which is controlled by the controller  232 . The voltage limiter  244  may be configured to limit the voltage of PV module  124  to within limits established by the Underwriters Laboratories (UL) during a GWIC procedure. 
         [0039]    The AMS  128  may also include a voltage monitor (VM)  252  coupled with the positive interconnect  208  and the controller  232 . The voltage monitor  252  may be used to continuously monitor a voltage associated with the PV module  124  and provide an indication of the monitored voltage to the controller  232 . The controller  232  and/or SC  104  may use the indication of the monitored voltage to detect a total module bypass condition or full module voltage drop due to ground faults as will be discussed in further detail below. 
         [0040]    The AMS  128  may also include a module bypass  256  coupled to the positive interconnect  208  and the negative interconnect  212 . The module bypass  256  may be a bypass diode that is used to bypass the PV module  124  when an N-switch  258  is opened (or has failed). The N-switch  258  may be an N-type metal-oxide semiconductor (MOS) switch, controlled by the controller  232 , to cause the PV module to be selectively bypassed as is discussed in the procedures below. 
         [0041]    The AMS  128  may also include a ground relay switch  260 , controlled by the controller, and electrically coupled with the buffer/filter  224  and a frame ground. The ground relay switch  260  may be closed to isolate the AMS  128  from high voltages during installation or in an emergency event. 
         [0042]    The AMS  128  may also include an identifier block (IB)  264  coupled with the controller  232 . The identifier block  264  may store one or more identifiers that may be used to uniquely identify the AMS  128  and/or the PV module  124 . These identifiers may be used to prevent the use of stolen and/or unauthorized components within the PV installation  100 . In some embodiments, the identifier block  264  may store one or more serial numbers. 
         [0043]      FIG. 4  is a block diagram of the SC  104  in accordance with some embodiments. The SC  104  may include, in addition to the components previously introduced in  FIG. 1 , a ground fault detector (GFD)  404 ; a ground fault current limiter (GFCL)  408 ; and a string current limiter (SCL)  412  in accordance with some embodiments. 
         [0044]    The SMU controller  152  may include a controller  416  coupled with a buffer/ADC  418  and transceiver  420 . The controller  416  may cooperatively interact with the transceiver  420  to receive status information (e.g., current and/or voltage measurements) from, and transmit control information (e.g., command messages) to, the AMSs  128 . The controller  416  may also be coupled to a user interface  424  that may include a display, to provide an indication of status information, and/or a user input device, to receive controls and/or configuration information from a user. 
         [0045]    The controller  416  may also be coupled to the GFD  404 , a GF test switch  432 , and a string ID switch  436  to facilitate mapping and ground fault detection, isolation and location procedures discussed below. 
         [0046]    The SMU controller  152  may also include a serial communication interface (SCI)  440  configured to communicatively couple the SC  104  to the ALG  116 . 
         [0047]    The SMU controller  152  may also include a VR  444  configured to condition the voltage provided to the electronic components of the SMU controller  152 . 
         [0048]      FIG. 5  is a block diagram of an SMU  136  in accordance with some embodiments. The SMU  136  may include a current sensor  504 - 1  on a positive SMU line  508 , which may be electrically coupled with the positive string interconnect  144  through a blocking/bypass block  512 - 1 . A bypass portion of the blocking/bypass block  512 - 1  may reduce power dissipation in a blocking diode of the blocking/bypass block  512 - 1  during normal operation. 
         [0049]    The SMU  136  may also include a current sensor  504 - 2  on a negative SMU line  516 , which is electrically coupled to the negative string interconnect  148  through blocking/bypass block  512 - 2 . 
         [0050]    The SMU  136  may also include a buffer/filter  520  that is electrically coupled to the current sensors  504 , a point  524 , a point  528 , and a system ground. The buffer/filter  520  may remove voltage transients and noise from voltage/current measurements prior to sampling by ADC  532 . The sampled measurements may be provided from the ADC  532  to a controller  536 , which may in turn, be provided to the SMU controller  152 . The controller  536  may also be coupled with the blocking/bypass blocks  512 . 
         [0051]    The PV installation  100  may provide a number of capabilities beneficial to both an installer and an operator of the PV installation  100 . In some embodiments, the PV installation  100  may provide mapping capabilities in which a complete map of the topology of the PV installation  100  may be discovered. This may facilitate rapid identification of installation errors and abnormalities that may occur in the PV installation  100  during operation. In some embodiments, the PV installation  100  may provide power monitoring capabilities. For example, during normal operation the power output of each individual PV module  124  may be available over a network through the ALG  116 . This may allow rapid identification of failing modules, data logging to facilitate measuring long term power degradation, etc. 
         [0052]    In some embodiments, the PV installation  100  may provide string monitoring capabilities. For example, during normal operation any damage or degradation of the wiring between PV modules  124  may be detected and its location determined. 
         [0053]    In some embodiments, the PV installation  100  may provide theft detection capabilities. For example, the disappearance of one or more PV modules  124  from the PV installation  100  may be instantly detected and reported over the network through the ALG  116 . This capability may also be provided at night when the PV modules  124  themselves are not producing power. 
         [0054]    At least some of these and other capabilities will be described with respect to the procedures discussed below. Variables discussed within these descriptions may be provided in Table 1. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Name 
                 Definition 
                 Description 
               
               
                   
               
             
             
               
                 S_Vp(N) 
                 M+ - M− 
                 M+ voltage of the N th  PV module in a 
               
               
                   
                   
                 string (PV module (N)) 
               
               
                 S_VstrP(N) 
                 FGND - M− 
                 Non-inverted M− voltage of PV module (N) 
               
               
                 S_VstrM(N) 
                 M− - FGND 
                 Inverted M− voltage of PV module (N) 
               
               
                 S_Ip(N) 
                   
                 Current through PV module (N) 
               
               
                 P_Vstr 
                   
                 Full string voltage 
               
               
                 P_IstrP 
                   
                 Full string current at positive string 
               
               
                   
                   
                 interconnect 
               
               
                 P_IstrM 
                   
                 Full string current at negative string 
               
               
                   
                   
                 interconnect 
               
               
                 P_Vgnd 
                   
                 Voltage developed between system 
               
               
                   
                   
                 ground and negative string 
               
               
                   
                   
                 interconnect 
               
               
                   
               
             
          
         
       
     
         [0055]    Where FGND is the frame ground. 
         [0056]      FIG. 6  is a flow diagram  600  of operations within a mapping procedure in accordance with some embodiments of the disclosure. 
         [0057]    At block  604  (“Associating AMSs with SCs”), the mapping procedure may include the SC  104  identifying and associating with the AMSs  128  that are electrically coupled to the SC  104 . The SC  104  may establish and maintain a radio hub with the AMSs  128  to allow wireless communication between the SC  104  and the AMSs  128 . Each radio hub may have a unique hub identifier (ID) and be isolated from other radio hubs even if they are in the same radio space. In some embodiments, the SMU controller  152  may transmit a broadcast association message that includes the hub ID. AMSs  128  that are coupled to the SC  104  and, therefore, part of its radio hub, may receive the broadcast association message and adopt the hub ID of the broadcast message. AMSs that are not coupled to the SC  104  and, therefore, not part of its radio hub, may be turned off during the time the broadcast association message is sent from the SC  104  in order to prevent their adoption of the hub ID of the SC  104 . If an AMS that is not coupled to the SC  104  has already adopted a hub ID of its associated SC, it may be left on and simply ignore the broadcast association message from the SC  104 . 
         [0058]    In some embodiments, if a hub ID associated with an AMS  128  is to be changed, e.g., due to incorrect initial association, the AMS  128  being moved to a different hub, etc., the AMS  128  may first receive a special message from SC  104  instructing it to discard its hub ID. Afterward, it may re-associate with another radio hub. 
         [0059]    As used herein, instructions to the AMSs  128  (and other components) from the SC  104  (or other components) may be in the form of command messages sent over appropriate coupling paths. 
         [0060]    At block  608  (“Associating AMSs with strings”), the mapping procedure may include the SC  104  associating each PV module  124  with its respective string  140 . This may be done by the SMU controller  152  transmitting a series of command messages to the AMSs  128  to operate their respective N-switches  258  to selectively connect or disconnect corresponding PV modules  124  to the string  140 . In some embodiments, the SMU controller  152  may instruct all of the AMSs  128  to control their N-switches  258  to disconnect their corresponding PV modules  124  from the strings  140 . A particular AMS, e.g., AMS  128 - 1 , may then be selected at random and instructed, by the SMU controller  152 , to control its N-switch  258  to connect its PV module  124 - 1  to the string  140 - 1 . The SMU controller  152  may then instruct another AMS  128  to control its N-switch  258  to connect its PV module  124  to an undetermined string  140 . If the undetermined string  140  is string  140 - 1 , the SC  104  may sense a non-zero voltage change, e.g., an increase, in the full string voltage, and the SMU controller  152  may determine that the tested PV module  124  is also on string  140 - 1 . In this manner, the SMU controller  152  may work through each of the remaining AMSs  128  to determine which are associated with string  140 - 1 . After all of the AMSs  128  of string  140 - 1  are identified, the SMU controller  152  may instruct all but one of the AMSs  128  not associated with string  140 - 1  to control their N-switches  258  to disconnect their corresponding PV modules  124  from the strings  140  and the process may be repeated. If there is any AMS  128  that is not accounted for after the SMU controller  152  works through all of the strings  140  coupled with the SC  104 , then there may be a faulty connection. 
         [0061]    At block  612  (“Determining interconnection order of AMS”), the mapping procedure may include the SC  104  determining the interconnection order of the AMSs  128  in the strings  140 . This may be determined by grading values of voltages across M− terminals and the frame ground, i.e., S_VstrM values. In particular, the PV modules  124  closer to the SC  104  may have larger S_VstrM values. The S_VstrM values may be determined by the various AMSs  128  and reported to the SMU controller  152 . 
         [0062]    At block  616  (“Associating strings to SMUs”), the mapping procedure may include the SC  104  associating each of the strings  140  with a respective SMU  136  in the SC  104 . The SMU controller  152  may instruct, e.g., AMS  128 - 1  in string  140 - 1  to control its N-switch  258  to connect PV module  124 - 1  to string  140 - 1 . The SMU controller  152  may then turn on the string identification (ID) switch  436 . The SMU controller  152  may then identify which SMU  136  has a current sensor  504  that records a current, e.g., SMU  136 - 1 . SMU  136 - 1  may then be associated with the string under test, e.g., string  140 - 1 . The SMU controller  152  may then instruct AMS  128 - 1  to control its N-switch  258  to disconnect PV module  124 - 1  from the string  140 - 1  and the process may be repeated with respect to the remaining strings  140  until all of the strings  140  are associated with a corresponding SMU  136 . 
         [0063]      FIG. 7  is a flow diagram  700  of operations within a ground fault (GF) detection procedure in accordance with some embodiments of the disclosure. In particular, the flow diagram  700  may refer to detection of a low-resistance GF at the time of installation. 
         [0064]    At block  704  (“Turning on GF test switch”), the SMU controller  152  may turn on the GF test switch  432 , which should result in the string current of the negative string interconnect  148  going to zero. 
         [0065]    At block  708  (“Connecting PV module (N)”), the SMU controller  152  may transmit a command message to a first AMS, e.g., AMS  128 - 1  to control its N-switch  258  to connect the PV module  124 - 1  to string  140 - 1 . 
         [0066]    At block  712  (“P_IstrM&lt;&gt;0”), the SMU controller  152  may determine whether the negative string interconnect  148  registers a current. If so, then the SMU controller  152  may provide an indication of a ground fault of PV module  124 - 1  at block  716  (“Providing indication of GF at PV module (N)”). If P_IstrM does not register a current, the SMU controller  152  may provide an indication of no GF of AMS  128 - 1  at block  720  (“Providing indication of no GF at PV module (N)”). An indication of a GF (or no GF) may include, e.g., a status report/alert sent to user interface  424 . In some embodiments, an indication of no GF may be implied through a non-indication of a GF. 
         [0067]    At block  724  (“Disconnecting PV module (N)”), the SMU controller  152  may transmit a command message to the AMS  128 - 1  to control its N-switch  258  to disconnect PV module  124 - 1 . This procedure of flow diagram  700  may be repeated for each of the managed modules  132 . 
         [0068]      FIG. 8  is a flow diagram  800  of operations within a ground fault detection procedure in accordance with some embodiments of the disclosure. In particular, the flow diagram  800  may refer to detection of a high-resistance ground fault at the time of installation. In some embodiments, this may be done after the low-resistance GF test shown in flow diagram  700 . 
         [0069]    At block  804  (“Connecting all PV modules in string”), the SMU controller  152  may transmit a command message to all of the AMS of a given string, e.g., AMS  128 - 1 - 128 - 3  of string  140 - 1  to control their N-switches  258  to connect their corresponding PV modules  124  to the string  140 - 1 . 
         [0070]    At block  808  (“Turning on ground relay in AMS (N)”), the SMU controller  152  may transmit a command message to an AMS (N) to turn on its ground relay switch  260 . 
         [0071]    At block  812  (“S_VstrP(N)&lt;&gt;0”), the SMU controller  152  may determine whether a voltage across the frame ground and the M− terminal of PV module (N) registers a value, i.e., whether S_VstrP(N)&lt;&gt;0. This may be done by the SMU controller  152  receiving a status message from the first AMS (N). If so, then the SMU controller  152  may provide an indication of a ground fault with respect to PV module (N) at block  816  (“Providing indication of GF at PV module (N)”). If S_VstrP(N) does not register a value, the SMU controller  152  may provide an indication of no GF at PV module (N) at block  820  (“Providing indication of no GF at PV module (N)”). Similar to above, an indication of a GF (or no GF) may include, e.g., a status report/alert sent to user interface  424 . In some embodiments, an indication of no GF may be implied through a non-indication of a GF. 
         [0072]    At block  824  (“Disconnecting PV module (N)”), the SMU controller  152  may transmit a command message to the AMS (N) to control its N-switch  258  to disconnect PV module (N). This procedure of flow diagram  800  may be repeated for each of the remaining managed modules  132  of the string  140 - 1 . A similar procedure may also be done for the remaining strings  140 . 
         [0073]      FIG. 9  is a flow diagram  900  of operations within a ground fault detection procedure in accordance with some embodiments of the disclosure. In particular, the flow diagram  900  may refer to detection of a ground fault during operation of the PV installation  100 . This procedure may be used to quickly identify a ground fault and take a string  104  off-line thereby preventing a shutdown of the central inverter  108 . 
         [0074]    At block  904  (“|P_IstrP(N)-P_IstrM(N)|&gt;threshold”), the SMU controller  152  may monitor currents on a string  140  to determine whether the full string current at the positive string interconnect  144  is different from the full string current at the negative string interconnect  148  by a delta value greater than a predetermined threshold value, i.e., whether |P_IstrP(N)-P_IstrM(N)|&gt;threshold. The values of the string currents may be provided to the SMU controller  152  from the SMUs  136  where they are sensed. The predetermined threshold value may be set to a value that signifies a ground fault. If the delta value is greater than the predetermined threshold value, the SMU controller  152  may advance to block  908  to isolate and locate the GF. 
         [0075]    At block  908  (“Taking string (N) off-line”), the SMU controller  152  may send a command message to all of the AMSs  128  on string  140  to control their N-switches  258  to disconnect the PV modules  124  from the string  140  and to turn on their ground relay switches  260 . This may result, e.g., in the PV modules  124 - 1 - 124 - 3  being disconnected from the string  140 - 1 . 
         [0076]    At block  912  (“Retrieving stored values”), the SMU controller  152  may retrieve saved values of S_Ip(N). The SMU controller  152  may also retrieve, from the AMSs  128 - 1 - 128 - 3 , values of S_VstrP(N), S_VstrM(N), and S_Vp(N) from a point just prior to the point at which the PV modules  124  were disconnected. 
         [0077]    At block  916 , (“Determining location of GF”), the SMU controller  152  may proceed to determine where the ground fault occurred in the string  140 - 1 . 
         [0078]      FIG. 10  is a flow diagram  1000  of operations within a determining location of ground fault of block  916  in accordance with some embodiments of the disclosure. 
         [0079]    This determination may be initialized at block  1004  (“N=M”) by setting N equal to M, where M is the total number of PV modules  124  in the string  140 . 
         [0080]    At block  1008  (“S_Ip(N)&lt;&gt;P_IstrM”), it may be determined whether the current through PV module (N), which may be PV module  124 - 3  if N=M, is different from the full string current of the negative string interconnect  148 . If these currents are different, the ground fault may be in the wire connecting the PV module (N) to the PV module (N+1) or in the PV module (N) itself. When N is equal to M, the “PV module (N+1)” may refer to the SC  104  rather than an actual PV module  124 . If it is determined that these currents are different, in block  1008 , the procedure may advance to block  1012  (“S_VstrP(N)&lt;S_Vp(N)”). At block  1012 , the SMU controller  152  may determine whether a voltage across the frame ground and the M− terminal of the PV module (N) is less than a voltage across the M+ and M− terminals of PV module (N), i.e., whether S_VstrP(N)&lt;S_Vp(N). If so, the SMU controller  152  may then determine the ground fault is in the PV module (N) in block  1016  (“GF at PV module (N)”). Otherwise, the SMU controller  152  may determine that the ground fault is past PV module (N), e.g., in the wire connecting PV module (N) to PV module (N+1) or in PV module (N+1) itself, at block  1020  (“GF past PV module (N)”). 
         [0081]    Another indication that may be used by the SMU controller  152  to determine the ground fault is in PV module (N) may be to determine whether the value of the voltage across the M+ terminal and the M− terminal of the PV module (N) is significantly less than the open circuit voltage of PV module (N), Voc(N), i.e., whether S_Vp(N)&lt;&lt;Voc(N). If this condition is determinable, it may indicate that that the ground fault is in the PV module (N). In some embodiments, the condition of S_Vp(N)&lt;&lt;Voc(N), when determinable, may supersede the condition of S_VstrP(N)&lt;S_Vp(N). 
         [0082]      FIG. 11  is a flow diagram  1100  of operations within an open wiring detection procedure in accordance with some embodiments of the disclosure. In particular, the flow diagram  1100  may refer to detection and location of an open wire during operation of the PV installation  100 . 
         [0083]    At block  1104  (“Detecting open wire condition”), the SMU controller  152  may monitor the full string current at the negative string interconnect  148  and, when it goes to a value at or near zero, i.e., P_IstrM˜0, may determine that there is an open wire condition on string (N). 
         [0084]    At block  1108  (“Taking string off-line”), the SMU controller  152  may send a command message to all of the AMSs  128  on, e.g., string  140 - 1 , to control their N-switches  258  to disconnect the PV modules  124  from string  140 - 1  and to turn on their ground relay switches  260 . 
         [0085]    At block  1112  (“N=M”), N may be set to M. 
         [0086]    At block  1116  (“S_VstrP(N)-P_Vgnd˜0”), the SMU controller  152  may determine whether the difference between voltage across frame ground and M− terminal of the PV module (N) and the voltage across system ground and negative string interconnect  148  is at or near zero, i.e., S_VstrP(N)-P_Vgnd˜0. If so, the SMU controller  152  may determine the open wire is between PV module (N) and PV module (N+1) at block  1120  (“Determining open wire between PV module (N) and PV module (N+1)”). Again, if N+1 is greater than M, than PV module (N+1) may refer to the SC  104 . If the SMU controller  152  determines, at block  1116 , the difference between voltage across frame ground and M− terminal and the voltage across system ground and negative string interconnect  148  is not at or near zero, the SMU controller  152  may determine that the open wire is before PV module (N) at block  1124  (“Determining open wire before PV module (N)”). 
         [0087]      FIG. 12  is a flow diagram  1200  of operations within a weak wire detection procedure in accordance with some embodiments of the disclosure. In particular, the flow diagram  1200  may refer to detection of a weak wire in power and/or ground wires during operation of the PV installation  100 . 
         [0088]    At block  1204  (“N=M”), the SMU controller  152  may set N equal to M. 
         [0089]    At block  1208  (“(S_VstrM(N)&lt;&gt;S_Vp(N−1)+S_VstrM(N−1)”), the SMU controller  152  may determine whether the voltage across the M− terminal of PV module (N) and the frame ground is different from the sum of voltage across the M+ and M− terminals of PV module (N−1) and voltage across the M− terminal of the PV module (N−1) and the frame ground, i.e., whether (S_VstrM(N)&lt;&gt;S_Vp(N−1)+S_VstrM(N−1). If so, the SMU controller  152  may determine that the wire between PV module (N) and PV module (N−1) is resistive at block  1212  (“Determining wire between PV module (N) and PV module (N−1) is resistive”). If not, and if N is equal to M as initialized in block  1204 , then the SMU controller  152  may determine whether the sum of the voltage across the M+ and M− terminals of the PV module (M) and voltage across M− terminal of PV module (M) and the frame ground are greater than the full string voltage, i.e., whether (S_Vp(M)+S_VstrM(M))&gt;P_Vstr, at block  1216  (“(S_Vp(M)+S_VstrM(M)&gt;P_Vstr)”). If so, the SMU controller  152  may determine that the wire between the PV module (M) and the SC  104  is resistive at block  1220  (“Determining wire between PV module (M) and the SC  104  is resistive”). 
         [0090]    For the bottom PV module, e.g., PV module (0), the SMU controller  152  may determine whether a difference between the voltage across the frame ground and the M− terminal of the PV module (0) and the voltage across the system ground and the negative string interconnect  148  is greater than a voltage drop threshold value, i.e., whether (S_VstrP(0)-P_Vgnd)&gt;Voltage_drop_Threshold. If so, the SMU controller  152  may determine that the wire between PV module (0) and the SC  104  is resistive. The voltage drop threshold value may be a predetermined value that identifies a resistive condition. 
         [0091]    In various embodiments the SMU controller  152  may determine an existence and location, whether precise or approximate, of a variety of conditions that may occur at installation and/or operation of the PV installation  100 . An example, in addition to the ones discussed above, may include a determination that a fuse has blown, e.g., by determining that both a full string voltage, i.e., P_Vstr, and a full string current at the positive string interconnect, i.e., P_IstrP, are not equal to zero. Another example, may include determining the existence of a faulty blocking diode by measuring a voltage drop across the diode under test. If the voltage is zero, the diode may be determined to be shorted. If the voltage is greater than the normal voltage drop, the diode may be determined to be open. Yet another example may include determining an existence of a faulty bypass diode. This may be determined by determining that the M+ voltage of PV module (N) is significantly less than a maximum power voltage of PV module (N) (Vmp(N)), i.e., S_Vp(N)&lt;&lt;Vmp(N). If so, the SMU controller  152  may determine that the bypass diode of PV module (N) could be open. If it is determined that the M+ voltage of PV module (N) is significantly less than the open circuit voltage of PV module (N), i.e., S_Vp(N)&lt;&lt;Voc(N) when the module (N) is bypassed by turning on its N-switch  258 , then the SMU controller  152  may determine that the bypass diode may be shorted. 
         [0092]    Although certain embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of the disclosure. Those with skill in the art will readily appreciate that embodiments of the disclosure may be implemented in a very wide variety of ways. This disclosure is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments of the disclosure be limited only by the claims and the equivalents thereof.