Abstract:
A system and apparatus for interconnecting an array of power generating assemblies includes a cable assembly having a plurality of continuous conductors and a plurality of cable connectors electrically coupled to the continuous conductors. The continuous conductors are configured to receive inverter AC power generated by inverters and deliver the combined AC power to an AC grid or other power sink. The cable connectors are configured to mate with corresponding connectors of the inventers to deliver the AC power to the continuous conductors.

Description:
TECHNICAL FIELD 
     The present disclosure relates, generally, to a system and apparatus for delivering power from an array of power generating devices to a power sink and, more particularly, to an apparatus for delivering power from an array of DC-AC inverters to an AC grid. 
     BACKGROUND 
     Some power delivery systems comprise an array of power generation subassemblies whose combined output power is delivered to a power sink (a “power sink” being any device or apparatus that receives power from a power source). One example of such a system is a distributed photovoltaic power system in which each one of a plurality of solar panels is provided with a DC-AC inverter (“inverter”) that delivers power to an AC utility grid. Delivering the combined power from all of the inverters to the AC grid requires a suitable interconnection scheme. High operating efficiency, low cost, and reliable operation over long periods of time (e.g., twenty five years) may be highly valued features in such systems. 
     A typical way of interconnecting an array of photovoltaic inverters is illustrated in  FIG. 1 . As shown in  FIG. 1 , a distributed photovoltaic system  100  includes a plurality of photovoltaic panels  102  and associated inverters  104   a - 104   d . Power from the photovoltaic panels  102  is delivered to the inverters  104   a - 104   d  by PV interconnects  106 . Each inverter  104  may include a power input cable  108  and a power output cable  110 . The power input cables  108  are terminated in input connectors  112  and the power output cables  110  are terminated in output connectors  114  that mate with the input connectors  112 . Each power input connector  112  of each inverter  104  is connected to a power output connector  114  of an adjacent inverter  104  to form mated connectors  116  that may carry power between inverters. 
     A simplified schematic of the system  100  shown in  FIG. 1  for delivering power from inverters  104   a - 104   d  to a split-phase AC grid (e.g., a 240VAC grid comprising two 120VAC “hot” wires  130 ,  132  and a neutral wire  134 ) is shown in  FIG. 2 . As illustrated in  FIG. 2 , each inverter  104  includes inverter circuitry  140  that receives DC power from an associated photovoltaic panel  102  and delivers AC power by means of two internal “hot” wires  130   a ,  132   a  and an internal neutral wire  134   a . When the input connectors  112  and output connectors  114  of the inverters  104   a - 104   d  are coupled together to form mated connectors  116 , as shown in  FIGS. 1 and 3 , the input cables  108  and output cables  110  are “daisy chained” (i.e., the cables are connected in series) to form a split-phase power bus  150  that receives power from each of the inverters  104  and carries the combined power to the AC grid  152  (inverters having cables that are connected in this way are referred to herein as “series-connected inverters”). An interface cable  119 , connected to the output cable  110  of inverter  104   a , delivers the split-phase bus  150  into junction box  120 . The junction box  120  may be an electrical panel that connects to the AC grid or, as illustrated in  FIGS. 1 and 2 , it may provide a connection point between the wires of the split-phase bus  150  and the wiring  124  that connects to the AC grid  152  at a downstream panel (not shown). 
     Inverter circuitry  140  typically includes fuses and other protective devices, such as surge-protection devices, to protect the system  100  and components of the system  100  from transient electrical events and faults and to prevent failure of the entire system in the event of a failure in a single system subassembly (e.g., one of the inverters  104 ). One way to incorporate fuses and protective devices into a series-connected inverter  104  is illustrated in  FIG. 3 . As shown in  FIG. 3 , the inverter circuitry  140  includes a fuse  146  in series with each hot wire  130   a ,  132   a  and surge protection devices  154   a ,  154   b ,  154   c  (e.g., a metal-oxide varistor (“MOV”)) connected between each pair of wires  130   a ,  132   a ,  134   a.    
     Regulatory and safety requirements may also require that each inverter  140  be connected to earth ground. One way to provide an earth ground to each inverter  140 , illustrated in  FIGS. 1 and 2 , is to provide a ground wire  122  that is connected (e.g., by means of a screw) to each series-connected inverter. 
     SUMMARY 
     According to one aspect, a system for delivering power to an AC grid includes a first inverter, a second inverter, and a cable assembly. The first inverter may include a first inverter connector and the second inverter may include a second inverter connector. The first inverter may be configured to deliver inverter AC power via the first inverter connector and the second inverter may be configured to deliver inverter AC power via the second inverter connector. The cable assembly may be configured to receive power from the first and second inverters. The cable assembly may include a plurality of continuous conductors, a first cable connector, and a second cable connector. The plurality of continuous conductors may be configured to receive the inverter AC power delivered by the first and second inverters and deliver the combined power to the AC grid. The first cable connector may be electrically coupled to the plurality of continuous conductors and configured to mate with the first inverter connector to deliver the inverter AC power from the first inverter to the plurality of continuous conductors. Similarly, the second cable connector may be electrically coupled to the plurality of continuous conductors and configured to mate with the second inverter connector to deliver the inverter AC power from the second inverter to the plurality of continuous conductors. 
     In some embodiments, of the first and second inverters may include an inverter cable for delivering the AC power to the respective first and second inverter connector. Each inverter cable may include a plurality of cable conductors for carrying the inverter AC power. The plurality of cable conductors may have a current-carrying capacity less than a current-carrying capacity of the continuous conductors. 
     The cable assembly may include a protective circuit element. The protective circuit element may be adapted to carry inverter AC power between the first cable connector and one of the plurality of continuous conductors. In some embodiments, the protective circuit element may be electrically coupled to a first continuous conductor of the plurality of continuous conductors and a second continuous conductor of the plurality of continuous conductors. In some embodiments, the protective circuit element may be embodied as a fuse. In other embodiments, the protective circuit element may be embodied as a surge protection device. For example, the surge protection device may be a metal-oxide varistor. 
     In some embodiments, the system may further include a replaceable series element connected between the first inverter connector and the first cable connector. The replaceable series element may include a protective circuit element. The replaceable series element may be configured to carry inverter AC power between the first inverter connector and the first cable connector. In some embodiments, the protective circuit element may be electrically coupled to a first continuous conductor of the plurality of continuous conductors and a second continuous conductor of the plurality of continuous conductors. The protective circuit element may be embodied as a fuse. Alternatively, the protective circuit element may be embodied as a surge protection device such as, for example, a metal-oxide varistor. 
     In some embodiments, the system may further include a photovoltaic module. In such embodiments, the first inverter may be electrically coupled to the photovoltaic module to receive input power therefrom. Additionally, the plurality of continuous conductors may include three or four continuous conductors. Further, in some embodiments, the plurality of continuous conductors may include an earth ground continuous conductor. 
     According to another aspect, a cable assembly for delivering power from one or more power generation sources to an AC grid may include a plurality of continuous conductors, a first cable connector, a second cable connector, and a replaceable series element. The continuous conductors may be configured to receive power from the power generation sources and delivering the power to the AC grid. The first cable connector may be electrically coupled to the plurality of continuous conductors and configured to couple with a first power generation source to receive source AC power therefrom. Similarly, the second cable connector may be electrically coupled to the plurality of continuous conductors and configured to couple with a second power generation source to receive source AC power therefrom. The replaceable series element may be adapted to carry AC power between the first power generation source and the first cable connector. 
     In some embodiments, the first power generation source may include a source connector and the replaceable series element may be connected between the source connector and the first cable connector. In such embodiments, the replaceable series element may include a protective circuit element. The replaceable series element may be configured to carry source AC power between the source connector and the cable connector. Additionally, the protective circuit element may be electrically coupled to a first continuous conductor of the plurality of continuous conductors and a second continuous conductor of the plurality of continuous conductors. 
     The protective circuit element may be embodied as a fuse. Alternatively, the protective circuit element may be embodied as a surge protection device such as, for example, a metal-oxide varistor. Additionally, in some embodiments, the system may further include a photovoltaic module. In such embodiments, the first inverter may be electrically coupled to the photovoltaic module to receive input power therefrom. Additionally, the plurality of continuous conductors may include three or four continuous conductors. Further, in some embodiments, the plurality of continuous conductors may include an earth ground continuous conductor. 
     According to a further aspect, a system for delivering AC power to a power sink may include a plurality of inverters and a cable assembly. Each inverter may include a inverter connector for delivering power from the inverter. The cable assembly may include a plurality of separable cable connectors and a first cable end. Each separable cable connector may be configured to separably mate with one of the inverter connectors to receive AC power from the corresponding inverter. The first cable end may be configured to deliver the combined power received from the plurality of inventors to the power sink. Additionally, the cable assembly may be configured such that the AC power delivered by each inverter to the power sink passes through only one separable cable connector between the respective inverter and the first cable end. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a distributed photovoltaic power system; 
         FIG. 2  is a simplified schematic of the system of  FIG. 1 ; 
         FIG. 3  is a schematic of protective circuitry for an inverter of the system of  FIG. 1 ; 
         FIG. 4  is a perspective view of a distributed photovoltaic power system according to the present disclosure; 
         FIG. 5  is a simplified schematic of one embodiment of the system of  FIG. 4 ; 
         FIG. 6  is a simplified schematic of one embodiment of protective circuitry of the system of  FIG. 4 ; 
         FIG. 7  is a perspective view of one embodiment of a portion of the system of  FIG. 4  including a series replaceable element; 
         FIG. 8  is a simplified schematic of one embodiment of protective circuitry of the series replaceable element of  FIG. 7 ; 
         FIG. 9  is a simplified schematic of a portion of the system  100  of  FIG. 4  including one embodiment of an earth grounding interconnection; 
         FIG. 10  is a simplified schematic of a portion of the system  100  of  FIG. 4 , including one embodiment of a series replaceable element and an earth grounding interconnection; 
         FIGS. 11   a - 11   c  are simplified illustrations of various embodiments of tapped connections; and 
         FIG. 12  is an illustration of one embodiment of an overmolded tapped connection. 
     
    
    
     DETAILED DESCRIPTION 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Referring now to  FIGS. 4 and 5 , in one embodiment, a distributed photovoltaic system  200  includes a plurality of photovoltaic panels  202  and associated inverters  204   a - 204   d . Although the illustrative system  200  includes four photovoltaic panels  202  and associated inverters  204 , it should be appreciated that system  200  may include two, three, or more panels  202  and associated inverters  204  in other embodiments. Power from the photovoltaic panels  202  is delivered to the inverters  204  by PV interconnects  206 . Each inverter  204   a - 204   d  includes a power delivery cable  210  terminated in a power delivery connector  212 . For ease of comparison with the system  100  of  FIGS. 1 and 2 , the system  200  of  FIGS. 4 and 5  is configured to deliver power from inverters  204   a - 204   d  to a split-phase AC grid (e.g. a 240VAC grid comprising two 120VAC “hot” wires and a neutral wire). However, in other embodiments, the system  200  may be configured to deliver power to other power sinks. 
     The system  200  includes a power delivery cable assembly  220  to which each of the inverters  204  is electrically coupled via a corresponding power delivery cable  210 . The power delivery cable assembly  220  delivers the power received from each of the inverters  204  to an the AC grid via an AC junction box  240 , which may be an electrical panel that connects to the AC grid or, as illustrated in  FIGS. 4 and 5 , may provide a connection point between bus conductors  230 ,  232 ,  234  and wiring  224  that connects to an AC grid at a downstream panel (not shown). 
     The power delivery cable assembly  220  includes a power delivery bus  250 , embodied as a plurality of continuous conductors  230 ,  232 ,  234 , and two or more tap connection junctions  222 . Each of the inverters  204  are electrically coupled to the power delivery bus  250  to supply power thereto via one of the tap connection junctions  222 . The tap connection junctions  222  each include a power bus connector  214  configured to mate with the power delivery connector  212  of the corresponding inverter  204  to form a mated tap connection  280  (mated terminals within each mated tap connection  280  in  FIG. 5  are indicated by an “x”). Each of the continuous conductors  230 ,  232 ,  234  may be embodied as any type of conductor capable of conducting electricity including, but not limited to, a plurality of wires such as braided wire, mono-strand wire, a bus bar, and/or other conductive structures. As used herein, the term “continuous conductor” means an electrical conductor having no in-line separable connection between a first end of the electrical conductor and a second end of the electrical conductor. For example, the illustrative continuous conductors  230 ,  232 ,  234  extend from a first end  226  of cable assembly  220  to the remote-most tap connection junction  222  with no interposed separable connection between the first end  226  and the remote-most junction  222 . As such, AC power received from each inverter  204  is delivered to the first end  226  (and, in  FIG. 4 , thence to the AC junction box  240 ) by passing through a single separable connector (i.e., the respective power bus connector  214 ) between the respective inverter  204  and the box  240 . Conversely, the power bus  150  of the system  100  illustrated in  FIGS. 1-3  includes multiple in-line, mated connectors  116 . As such, power delivered from, for example, the remote-most inverter  104   d  of the system  100  passes through multiple connectors  116  between the inverter  104   d  and the junction box  120 . 
     It should be appreciated that the particular length of the continuous conductors  230 ,  232 ,  234  and/or the particular number of tap connection junctions  222  may vary depending on the particular implementation of the system  200 . It should also be appreciated that each inverter  204  may be “hard mounted” (e.g., via removable hardware, such as screws) in a position adjacent to its respective solar panel(s)  202  and that the number and relative physical positions of inverters  204  may vary considerably among different system  200  implementations. Use of flexible cables  210  on each inverter may provide flexibility with respect to the relative physical placement of inverters in different system configurations and allow a particular power cable  220  design to accommodate a wide range of physical system configurations. 
     Each of the tap connection junctions  222  includes corresponding tap conductors  230   a ,  230   b ,  230   c , which are electrically coupled to and tap off of the continuous conductors  230 ,  232 ,  234 , respectively. As such, power is delivered from each inverter  204   a - 204   d  to the power delivery bus  250  (i.e., to continuous conductors  230 ,  232 ,  234 ) via an associated power delivery cable  210 , a mated tap connection  280 , and tap conductors  230   a ,  230   b ,  230   c . An inverter  204   a - 204   d  of the kind shown in  FIGS. 4 and 5  is referred to herein as a “tap-connected inverter”. 
     In contrast to the system of  FIGS. 1 and 2 , in which input and output connectors  112 ,  114  on series-connected inverters  104   a - 104   d  form separable mated connections  116  that are serially connected within the daisy-chained bus  150 , the tap-connected inverters  204  in the system  200  of  FIGS. 4 and 5  are connected via conductive connections (i.e., tap conductors  230   a ,  230   b ,  230   c ) that tap off of the continuous conductors  230 ,  232 ,  234 . It should be appreciated that use of taps and continuous conductors, instead of daisy-chained serial connectors, may result in improved efficiency because each mated tap connections  280  carry, on average, less power than mated connectors  116 , and hence may have lower losses. In addition, failure of a mated tap connection  280  in the system  200  may result in loss of power delivery from only the affected inverter  204 , whereas failure of a mated connector  116  in the system  100  of  FIGS. 1 and 2  may result in loss of power delivery from many, and possibly all, upstream inverters  104 . Thus the system  200  may exhibit improved reliability and availability compared to the system  100  of  FIGS. 1 and 2 . 
       FIGS. 11A through 11C  show illustrative embodiments of structures and methods for forming a tap connection to the power delivery bus  250 . It should be appreciated that in each there are no separable connectors interposed along the length of a continuous conductive path. 
     Referring now to  FIG. 11A , in one embodiment, the power delivery bus  250  is embodied as a plurality of insulated path wires  231 ,  233 ,  235 , which comprise, respectively, continuous conductors  230 ,  232 ,  234  (e.g., copper wires); likewise, insulated tap wires  231   a ,  231   b ,  231   c  comprise, respectively, tap conductors  230   a ,  230   b ,  230   c  (e.g., copper wires). To electrically coupled the tap conductors  230   a ,  230   b ,  230   c  to the continuous conductors  230 ,  232 ,  234 , insulation is removed from regions  260   a ,  260   b ,  260   c  of each insulated path wire  231 ,  233 ,  235  to expose a portion of the respective continuous conductors  230 ,  232 ,  234 ; likewise, an end of each tap wire  231   a ,  231   b ,  231   c  is stripped of insulation to expose an end portion of respective tap conductors  230   a ,  230   b ,  230   c . The end of each tap conductor is electrically connected to a respective conductive paths  230 ,  232 ,  234  (e.g., by solder) to form a tap connection (three are shown). 
     In another embodied as illustrated in  FIG. 11   b , a tap connection (only one is shown) is formed by connecting (e.g., by twisting, soldering) the stripped and uninsulated conductors  230   x ,  230   y ,  430   a  from three insulated wires  331   a ,  331   b  and  431   a . Connected in this way, the conductors  331   a  and  331   b  form a portion of continuous conductive path  230  and conductor  430   a  forms a tap conductor. 
     Additionally, in another embodiment as illustrated in  FIG. 11   c , a tap connection is formed by crimping together (e.g., by use of a parallel crimp connector  433 ) the stripped and insulated conductors  230   x ,  230   y ,  430   a  from three insulated wires  331   a ,  331   b  and  431   a . Connected in this way, the conductors  331   a  and  331   b  form a portion of continuous conductive path  230  and conductor  430   a  forms a tap conductor. Further, in some embodiments, the insulated wire formed from wires  331   a ,  331   b  is initially cut and stripped to expose opposing ends of the conductors  230   x ,  230   y . The conductors  230   x ,  230   y  and the conductor  430   a  are subsequently electrically coupled together (e.g., via a crimped or soldered connection) to form a tap connection. 
     In some embodiments, as illustrated in  FIG. 12 , one or more of the tap junctions  222  of the cable assembly  220  may be overmolded to form an overmolded tap junction  500 . By overmolding the tap junction, the resiliency to environmental effects of the cable assembly  220  is increased. For example, as shown in  FIG. 12 , the power bus connector  214  of the overmolded tap junction  500  is inset or otherwise overmolded to reduce the likelihood of incursion of debris, water, and/or the like. Any suitable molding process may be used to form the overmolded tap junction  500 . 
     In the system  200 , each tap-connected inverter  104   a - 104   d  may comprise a single cable  210 , instead of the pair of cables  108 ,  110  associated with each series-connected inverter  104   a - 104   d  in the prior art system  100 . Furthermore, in normal operation, the power delivery cables  210  and connectors  212 ,  214  in the system  200  may only need to be sized to carry the power that can be delivered by a single inverter, whereas the cables  108 ,  110  and connectors  112 ,  114  in the prior-art system  100  must be sized to carry the full rated power of the entire array of inverters  104   a - 104   d . For example, in the prior art system, all of the inverter cables  108 ,  110  may comprise #12 AWG conductors with equivalently rated connectors, whereas in some embodiments of the system  200  the inverter cable  210  may comprise smaller #18AWG conductors with correspondingly smaller connectors. Thus, a system according to the present disclosure may be more cost-effective than a prior art daisy-chained system  100 . 
     In some embodiments, protective circuit elements may be incorporated in the power delivery system  200  as illustrated in  FIG. 6 , which shows a portion of the region of the power delivery cable  220  that is labeled “A” in  FIGS. 4 and 5 . As illustrated in  FIG. 6 , fuses  246  and surge protectors  254   a - 254   c  are installed within tap connection junction  222 . It should be appreciated that by locating fuses in the tap connection junction, as opposed to locating fuses in the inverter (e.g., as shown in  FIG. 3  for a prior art system  100 ), a short circuit in an inverter cable (which may happen if a cable is, e.g., chewed by a pest, such as a rodent or squirrel) may affect only a single inverter. Additionally, it should be appreciated that the magnitude of a fault current that the cable  210  may have to carry may be limited by the rating of the fuse, thereby allowing use of smaller conductors in the cable  210 . 
     In other embodiments, protective circuit elements may be incorporated in the power delivery system  200  as illustrated in  FIGS. 7 and 8 . As illustrated in  FIG. 7 , which shows the portion of the system  200  that is labeled “A” in  FIG. 4 , a replaceable series element  300  comprises connector  314  that connects to power delivery connector  212  at the end of cable  210 , and connector  312  that connects to power bus connector  214  at tap connection junction  222 . As shown in  FIG. 8 , circuit protective elements, such as fuses  246  and surge protectors  254   a - 254   c , may be installed within the replaceable series element  300 . Use of the replaceable series element  300  offers the same benefits discussed above with respect to  FIG. 6  and may also simplify replacement of protective elements and also simplify the design of the power delivery cable  220  (by eliminating the need for circuit protective elements, and means for accessing those elements, if provided, within the cable assembly). Replaceable series elements may also be configured as extenders to increase the length of inverter cables  210 ; such extender cables may be configured to also include protective elements. 
     Additionally, in some embodiments, an earth ground may be provided to an inverter  204  in the power delivery system  200  as illustrated in  FIGS. 9 and 10 , each of which shows the portion of the system  200  that is labeled “A” in  FIGS. 4 and 5 .  FIG. 9  shows a portion of a system  200  comprising a power delivery cable  220  that incorporates circuit protective elements (not shown in detail in  FIG. 9 , but indicated by the element  410 ) within a tap connection junction  222 ;  FIG. 10  shows a portion of a system  200  in which a replaceable series element  300  comprises circuit protective elements (not shown in detail in  FIG. 10 , but indicated by the element  410 ). In  FIGS. 9 and 10 , the power delivery cable  220  comprises an earth ground bus conductor  450  and the inverter cable  210  comprises an inverter earth ground conductor  450   a  that is connected to a earth grounding point  290  within inverter  204   c . In  FIG. 9  the earth ground bus conductor  450  connects to inverter earth ground conductor  450   a  via the mated tap connection  280 ; in  FIG. 10  the earth ground bus conductor  450  connects to inverter earth ground conductor  450   a  via the mated tap connection  280  and a ground conductor  450   b  in replaceable series element  300 . 
     It is understood that reference to photovoltaic systems is illustrative and that the present disclosure is equally applicable to a variety of power delivery system embodiments, e.g., systems comprising fuel cells or other power generation sources. It should also be understood although the drawings illustrate power generating device arrays comprising a particular number of array elements, the present disclosure may be generally applicable to arrays including two or more power generating devices. 
     There is a plurality of advantages of the present disclosure arising from the various features of the apparatuses, circuits, and methods described herein. It will be noted that alternative embodiments of the apparatuses, circuits, and methods of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the apparatuses, circuits, and methods that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present invention as defined by the appended claims.