Abstract:
A system is provided including: (1) an arc fault circuit interrupter having a line side terminal and a load side terminal, wherein the line side terminal is coupled to a voltage source, and (2) a current source coupled to the load side terminal to backfeed the arc fault circuit interrupter. Numerous other aspects also are provided.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/365,982, filed Jul. 20, 2010, which is incorporated by reference herein in its entirety for all purposes. 
     
    
     BACKGROUND 
       [0002]    This application relates generally to systems and methods for providing arc fault and/or ground fault protection for distributed generation sources. 
         [0003]    In recent years, rising utility costs and growing concern regarding environmental harm caused by use of fossil fuels has spurred enhanced interest in “alternative” energy supplies, such as solar, wind, and hydroelectric power sources. In addition, as the cost of alternative energy sources has decreased, and as more electric utilities offer grid connected “net metering” programs that allow system owners to feed surplus electric power back to the electric utility, the use of alternative energy sources has increased. 
         [0004]    In a conventional residential net metering solar system, one or more photovoltaic panels are used to convert solar energy to a DC current, and one or more inverters convert the DC current to an AC current synchronized to the magnitude, phase and frequency of the voltage signal supplied by the electric utility. In a majority of installations, the generated AC signal is then fed into the home power distribution system (e.g., a circuit breaker panel) typically by back-feeding one or more conventional circuit breakers. 
         [0005]    A conventional circuit breaker typically is an electro-mechanical device that provides overload and short-circuit protection, but does not provide arc fault or ground fault protection. As a result, the wiring extending between the inverter and the home power distribution system is not protected against arc faults, but is capable of being subjected to such faults. 
         [0006]    Some previously known distributed generation sources have included arc fault and/or ground fault protection at or near the power sources, which are typically located on the roof of a building or at another location far away from the electrical panel. However, such sources typically are remotely located, often in severe weather environments, that are not always easy or convenient to access. As a result, such remotely-located arc fault and/or ground fault protection devices can be difficult to reset, maintain and replace. 
         [0007]    Accordingly, improved arc fault and/or ground fault protection for distributed generation sources is desirable. 
       SUMMARY 
       [0008]    In a first aspect of the invention, a system is provided including: (1) an arc fault circuit interrupter having a line side terminal and a load side terminal, wherein the line side terminal is coupled to a voltage source, and (2) a current source coupled to the load side terminal to backfeed the arc fault circuit interrupter. 
         [0009]    In a second aspect of the invention, a method is provided, the method including: (1) providing an arc fault circuit interrupter having a line side terminal and a load side terminal, wherein the line side terminal is coupled to a voltage source, and (2) coupling a current source to the load side terminal to backfeed the arc fault circuit interrupter. 
         [0010]    In a third aspect of the invention, a photovoltaic system is provided including: (1) an arc fault circuit interrupter having a line side terminal and a load side terminal, wherein the line side terminal is coupled to a voltage source, and (2) an inverter coupled to the load side terminal to backfeed the arc fault circuit interrupter. 
         [0011]    Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Features of the present invention can be more clearly understood from the following detailed description considered in conjunction with the following drawings, in which the same reference numerals denote the same elements throughout, and in which: 
           [0013]      FIG. 1  is a block diagram of a previously known system including an arc fault circuit interrupter device; 
           [0014]      FIG. 2  is a block diagram of an example back-fed arc fault circuit interrupter system in accordance with this invention; 
           [0015]      FIG. 3  is a more detailed block diagram of an example back-fed arc fault circuit interrupter system in accordance with this invention; 
           [0016]      FIG. 4A  is a block diagram of an alternative example back-fed arc fault circuit interrupter system in accordance with this invention; 
           [0017]      FIG. 4B  is a block diagram of another alternative example back-fed arc fault circuit interrupter system in accordance with this invention; 
           [0018]      FIG. 4C  is a block diagram of another alternative example back-fed arc fault circuit interrupter system in accordance with this invention; 
           [0019]      FIG. 5  is a block diagram of an example arc fault circuit interrupter device for use in systems in accordance with this invention; 
           [0020]      FIG. 6A  is a block diagram of an example photovoltaic system including a back-fed arc fault circuit interrupter device in accordance with this invention; and 
           [0021]      FIG. 6A  is a block diagram of an alternative example photovoltaic system including a back-fed arc fault circuit interrupter device in accordance with this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Systems and methods in accordance with this invention backfeed an arc fault circuit interrupter to provide arc fault (and/or ground fault) protection for a distributed generation source, such as a photovoltaic system, wind power system, hydroelectric system, generator, or other similar distributed generation source. 
         [0023]    An Arc Fault Circuit Interrupter (“AFCI”) is an electrical device designed to protect against fires caused by arcing faults in damaged or deteriorated electrical wiring. In a residential setting, such damage may be caused in wiring that is punctured, pinched, deteriorated, impaired, or otherwise damaged. To prevent such damaged wiring from causing arcs that may cause fires, modern electrical codes generally require AFCI circuit breakers in all circuits that feed outlets in bedrooms of dwelling units. 
         [0024]    For example,  FIG. 1  illustrates an example of a previously known system including an AFCI circuit breaker. In particular, system  10  includes an AFCI circuit breaker  12  installed in a load center  14 , such as a circuit breaker panel. For simplicity, AFCI circuit breaker  12  will be referred to as “AFCI  12 .” In the illustrated example, AFCI  12  is a single-pole AFCI circuit breaker. Persons of ordinary skill in the art will understand that AFCI  12  alternatively may be a two-pole AFCI circuit breaker. 
         [0025]    AFCI  12  includes “line side” terminals L, N and G, and “load side” terminals L′, N′ and G′. Through conventional connections in load center  14 , line side terminals L, N and G of AFCI  12  are connected to line, neutral and ground terminals of utility voltage source  16 , and load side terminals L′, N′ and G′ are connected to line, neutral and ground terminals of load  18 . Utility voltage source  16  is typically provided by an electrical utility provider. Load  18  is typically the electrical branch wiring to one or more electrical outlets. 
         [0026]    In normal operation, load side terminals L′, N′ and G′ are connected to line side terminals L, N and G via a normally-closed switch (not shown). In this regard, load  18  is normally coupled to utility voltage source  16 . As described in more detail below, AFCI  12  includes circuitry designed to detect arc faults on load side terminals L′, N′ and G′. If an arc fault is detected, an actuator (not shown) in AFCI  12  causes the switch to disconnect load side terminals L′, N′ and G′ from line side terminals L, N and G, thus de-energizing the circuit, and reducing the potential for fires. Thus, in  FIG. 1 , load side terminals are shown in cross-hatch to indicate that the terminals are protected against arc faults. 
         [0027]    Some AFCI devices, commonly referred to as dual function AFCI/GFCI devices, also include circuitry to detect ground faults. In such devices, if a ground fault is detected, the actuator in the AFCI devices causes the switch to disconnect load side terminals L′, N′ and G′ from line side terminals L, N and G. Thus, such AFCI devices provide both arc fault protection and ground fault protection of load side terminals L′, N′ and G′. 
         [0028]    In accordance with this invention, an AFCI is used to provide arc fault (and/or ground fault) protection for a distributed generation source, such as a photovoltaic system, wind power system, hydroelectric system, generator, or other similar distributed generation source. In particular, as described in more detail below, by back-feeding the AFCI using the distributed generation source, the AFCI may be used to provide arc fault (and/or ground fault) protection for a distributed generation source. 
         [0029]    Referring to  FIG. 2 , a first example system in accordance with this invention is described. In particular, example system  100  includes AFCI  12  installed in load center  14 , with line side terminals L, N and G of AFCI  12  connected to line, neutral and ground terminals of an AC voltage source  16 ′, and load side terminals L′, N′ and G′ connected to line (L″), neutral (N″) and ground (G″) terminals of AC current source  20 . In this regard, AC current source  20  back-feeds AFCI  12 . 
         [0030]    AFCI  12  may be any conventional AFCI circuit breaker, such as a Q120AFC arc fault circuit interrupter circuit breaker manufactured by Siemens Industry, Inc., New York, N.Y. 
         [0031]    AC voltage source  16 ′ may be a utility voltage source, such as utility voltage source  16  of  FIG. 1 . Alternatively, AC voltage source  16 ′ may be any other similar AC voltage source, such as a voltage source generator. For simplicity, AC voltage source  16 ′ will be assumed to be a utility voltage source. 
         [0032]    AC current source  20  may be a distributed generation source, such as a photovoltaic system, wind power system, hydroelectric system, generator, or any other similar distributed generation source that behaves like an AC current source. 
         [0033]    Although AFCI  12  is shown installed in load center  14  (e.g., in a circuit breaker panel inside a building or home), persons of ordinary skill in the art will understand that AFCI  12  alternatively may be installed in other locations, such as in an electrical subpanel, combination meter socket/load center, AC junction box, AC disconnect switch, or other similar location inside or outside a building or home. 
         [0034]    As mentioned above, AFCI  12  may be a single pole AFCI circuit breaker (“ 1 P AFCI”), or a two-pole AFCI circuit breaker (“ 2 P AFCI”). Referring now to  FIG. 3 , an example  2 P AFCI system in accordance with this invention is described. In particular, system  110  includes a  2 P AFCI  120  installed in load center  14 , and having line side terminals L 1 , N, and L 2 , and load side terminals load side terminals L 1 ′, N′ and L 2 ′. For simplicity, ground terminals are not shown. 
         [0035]    AFCI  120  may be any conventional AFCI circuit breaker, such as a Q120AFC arc fault circuit interrupter circuit breaker manufactured by Siemens Industry, Inc., New York, N.Y. 
         [0036]    Line side terminals L 1 , N, and L 2  are connected to line  1 , neutral and line  2  terminals of utility voltage source  16 , and load side terminals L 1 ′, N′ and L 2 ′ are connected to line  1  (L 1 ″), neutral (N″) and line  2  (L 2 ″) terminals of AC current source  20 . In this example, utility voltage source  16  and AC current source  20  are split-phase sources, with V 1  VAC between L 1 ′ and neutral, V 1  VAC between L 2 ′ and neutral, and 2×V 1  VAC between L 1 ′ and L 2 ′. AC current source  20  may be a photovoltaic system, wind power system, hydroelectric system, generator, or any other similar distributed generation source that behaves like a split-phase AC current source. 
         [0037]    For example as shown in  FIG. 4A , example system  110   a  includes a photovoltaic system  20   a  that is a 240V/120V split-phase system, such as for use in the United States. Alternatively, as shown in  FIG. 4B , example system  110   b  includes a wind turbine system  20   b  that is a 460V/230V split-phase system, such as for use in Europe.  FIG. 4C  illustrates yet another example system  110   c  that includes a current source generator  20   c  that is a 240V/120V split-phase system. 
         [0038]    Persons of ordinary skill in the art will understand that systems in accordance with this invention alternatively may be scaled to include more than one distributed generation source  20  coupled to one or more AFCI circuit breakers  12 / 120 . For example, a photovoltaic system  20   a  may be coupled to a  2 P AFCI  120 , and a wind turbine system  20   b  may be coupled to a  1 P AFCI  12  in single load center  14 . Furthermore, large renewable generation systems may be of sufficient ampacity to require multiple photovoltaic systems to be coupled to multiple AFCI circuit breakers to prevent overloading of any one electrical wire. 
         [0039]    Referring now to  FIG. 5 , an example AFCI  120  is described. AFCI  120  includes arc fault detector circuit  30 , actuator  32  and switches  34   a  and  34   b . Arc fault detector circuit  30  is coupled to load side terminals L 1 ′, N′, and L 2 ′, and includes one or more circuits designed to detect signal characteristics of arc faults on terminals L 1 ′ and L 2 ′. Although not shown in  FIG. 5 , arc fault detector circuit  30  also may include one or more circuits designed to detect ground faults between L 1 ′ and ground and L 2 ′ and ground. 
         [0040]    Arc fault detector circuit  30  is coupled to actuator  32 , which in turn is coupled to switches  34   a  and  34   b . Switches  34   a  and  34   b  are normally closed, so that load side terminals L 1 ′ and L 2 ′ are coupled to line side terminals L 1  and L 2 , respectively. If arc fault detector circuit  30  detects an arc fault (and/or a ground fault) on terminals L 1 ′, N′ or L 2 ′, arc fault detector circuit  30  causes actuator  32  to open switches  34   a  and  34   b  to disconnect load side terminals L 1 ′ and L 2 ′ from line side terminals L 1  and L 2 , respectively. 
         [0041]    Actuator  32  may be a solenoid, electromagnet, motor, magnetically actuated circuit breaker component, or other similar device that may be used to open switches  34   a  and  34   b  in response to a signal from arc fault detector circuit  30  indicating that an arc fault (and/or a ground fault) has occurred. 
         [0042]    Distributed generation sources that are designed for net-metering applications typically will include circuitry (sometimes called “anti-islanding” circuitry) that disconnects the distributed generation source from the electric utility voltage if the electric utility voltage drops below a predetermined value. This is a safety measure to prevent the distributed generation source from driving the electric utility power lines (and potentially injuring utility workers) in the event of a power failure. The disconnect is typically required to occur within a specified time (e.g., between about 50 ms and about 1500 ms) after loss of utility supply voltage, and is dependent upon system frequency and amperage. 
         [0043]    Thus, if line side terminals L 1 , N and L 2  in  FIG. 5  are coupled to an electric utility voltage source, and load side terminals L 1 ′, N and L 2 ′ are coupled to L 1 ″, N″, and L 2 ″ terminals of AC current source  20 , if arc fault detector circuit  30  detects an arc fault (and/or a ground fault) on terminals L 1 ′ or L 2 ′, actuator  32  will cause switches  34   a  and  34   b  to disconnect the utility supply from AC current source  20 . This in turn will trigger the anti-islanding circuits in AC current source  20  to disconnect AC current source  20  from load side terminals L 1 ′, N and L 2 ′ of AFCI  120 . 
         [0044]    Until the disconnect occurs, however, actuator  32  will remain energized at full load. Thus, to prevent damage to AFCI  120 , actuator  32  should be able to operate at full load until the anti-islanding circuitry in AC current source  20  disconnects AC current source  20  from load side terminals L 1 ′, N and L 2 ′ of AFCI  120 . For example, actuator  32  should be able to operate at full load for about 250 to about 1500 ms without failure, and should be appropriately matched to the disconnect time of the distributed generation source. 
         [0045]    As an alternative to making the solenoid able to operate at full load, it is also viable to pulse width modulate the signal to the actuator, switch the driving electronics from full-wave rectified to half-wave rectified, or to enable the actuator with a time limited square wave. 
         [0046]    As described above, systems and methods in accordance with this invention may be used with a variety of different distributed generation sources, such as photovoltaic systems. Referring now to  FIGS. 6A and 6   b , two example photovoltaic systems in accordance with this invention are described. 
         [0047]      FIG. 6A  illustrates an example system  110   a   1  that includes AFCI  120  installed in circuit breaker panel  14 , with a photovoltaic system  20   a   1  back-feeding AFCI  120 . Photovoltaic system  20   a   1  includes multiple photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , each of which is coupled to a corresponding micro-inverter  44   1 ,  44   2 , . . . ,  44   N . Each micro-inverter  44   1 ,  44   2 , . . . ,  44   N  converts DC current supplied by the corresponding photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , to AC current, which are combined at junction box  46 . Photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , micro-inverters  44   1 ,  44   2 , . . . ,  44   N  and junction box  46  may be located in a remote location (e.g., on a roof of a house). 
         [0048]    The output of junction box  46  feeds AC disconnect switch  48 , which may be mounted on the outside of a building or a home. The output of AC disconnect  48  back-feeds AFCI  120 . As illustrated in  FIG. 6A , AFCI  120  provides arc fault (and/or ground fault) protection to the conductors shown in cross-hatch. 
         [0049]    Referring now to  FIG. 6B , an alternative photovoltaic system in accordance with this invention is described. In particular,  FIG. 6B  illustrates an example system  110   a   2  that includes AFCI  120  installed in circuit breaker panel  14 , with a photovoltaic system  20   a   2  back-feeding AFCI  120 . 
         [0050]    Photovoltaic system  20   a   2  includes multiple photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , each of which is coupled to a combiner  52 . Combiner  52  combines the DC currents supplied by the photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , and the combined DC signal is coupled via DC disconnect  54  to string inverter  56 , which converts the DC input signal to an AC current. Photovoltaic panels  42   1 ,  42   2 , . . . ,  42   N , combiner  52 , DC disconnect  54  and string inverter  56  may be located in a remote location (e.g., on a roof of a house). 
         [0051]    The output of string inverter  56  feeds AC disconnect switch  48 , which may be mounted on the outside of a building or a home. The output of AC disconnect  48  back-feeds AFCI  120 . As illustrated in  FIG. 6B , AFCI  120  provides arc fault (and/or ground fault) protection to the conductors shown in cross-hatch. 
         [0052]    The foregoing merely illustrates the principles of this invention, and various modifications can be made by persons of ordinary skill in the art without departing from the scope and spirit of this invention.